Patent Publication Number: US-2023156357-A1

Title: Visual-inertial tracking using rolling shutter cameras

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 17/161,937 filed on Jan. 29, 2021, and claims priority to U.S. Provisional Application Ser. No. 63/045,568 filed on Jun. 29, 2020, the contents of both of which are incorporated fully herein by reference. 
    
    
     TECHNICAL FIELD 
     Examples set forth in the present disclosure relate to visual-inertial tracking. More particularly, but not by way of limitation, the present disclosure describes methods and systems for computing poses for images captured by rolling shutter cameras. 
     BACKGROUND 
     Rolling shutter cameras capture an image by rapidly scanning across a scene such that not all parts of the image are recorded at exactly the same instant. Artefacts may arise if there is relative movement between the camera and a scene during image acquisition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the various implementations disclosed will be readily understood from the following detailed description, in which reference is made to the appending drawing figures. A reference numeral is used with each element in the description and throughout the several views of the drawing. When a plurality of similar elements is present, a single reference numeral may be assigned to like elements, with an added lower-case letter referring to a specific element. 
       The various elements shown in the figures are not drawn to scale unless otherwise indicated. The dimensions of the various elements may be enlarged or reduced in the interest of clarity. The several figures depict one or more implementations and are presented by way of example only and should not be construed as limiting. Included in the drawing are the following figures: 
         FIG.  1 A  is a side view (right) of an example hardware configuration of an eyewear device suitable for use in a visual-inertial tracking system; 
         FIG.  1 B  is a perspective, partly sectional view of a right corner of the eyewear device of  FIG.  1 A  depicting a right visible-light camera, and a circuit board; 
         FIG.  1 C  is a side view (left) of an example hardware configuration of the eyewear device of  FIG.  1 A , which shows a left visible-light camera; 
         FIG.  1 D  is a perspective, partly sectional view of a left corner of the eyewear device of  FIG.  1 C  depicting the left visible-light camera, and a circuit board; 
         FIGS.  2 A and  2 B  are rear views of example hardware configurations of an eyewear device utilized in the augmented reality production system; 
         FIG.  3    is a diagrammatic depiction of a three-dimensional scene, a left raw image captured by a left visible-light camera, and a right raw image captured by a right visible-light camera; 
         FIG.  4    is a functional block diagram of an example visual-inertial tracking system including a wearable device (e.g., an eyewear device) and a server system connected via various networks; 
         FIG.  5    is a diagrammatic representation of an example hardware configuration for a mobile device of the augmented reality production system of  FIG.  4   ; 
         FIG.  6    is a schematic illustration of a user in an example environment for use in describing simultaneous localization and mapping; 
         FIG.  7    is a flow chart listing steps in an example method of displaying virtual objects in a physical environment; 
         FIGS.  8 A,  8 B,  8 C, and  8 D  are flow charts including steps of example methods of visual-inertial tracking with one or more rolling shutter cameras. 
     
    
    
     DETAILED DESCRIPTION 
     Various implementations and details are described with reference to examples including a system for providing visual-inertial tracking of an eyewear device with a first rolling shutter camera. The eyewear device includes a position determining system. Visual-inertial tracking is implemented by sensing motion of the eyewear device and obtaining an initial pose for the first rolling shutter camera, then capturing an image of an environment in which the image includes feature points. The movement of the mobile device is captured with a motion detector and a number of poses for the first rolling shutter camera are computed based on the initial pose and the sensed movement wherein each computed pose corresponds to a particular computed time. A computed pose is selected for each feature point by matching the particular capture time for the feature point to the particular computed time for the computed pose and the position of the mobile device is determined within the environment. 
     The more poses that are calculated for each readout of a rolling shutter camera generally improves the accuracy of the mobile device&#39;s estimated pose within the environment and therefore improves the perceived augmented reality (AR) experience for the user when content is rendered. Each calculation of a pose, however, consumes processing resources. In some situations (e.g., when the eyewear device is moving relatively slowly), acceptable AR results may be achieved with fewer poses than if the eyewear device were moving faster. By adjusting the number of poses calculated responsive to movement of the eyewear device, processing resources can be conserved when they are not necessary to produce acceptable results. 
     The following detailed description includes systems, methods, techniques, instruction sequences, and computing machine program products illustrative of examples set forth in the disclosure. Numerous details and examples are included for the purpose of providing a thorough understanding of the disclosed subject matter and its relevant teachings. Those skilled in the relevant art, however, may understand how to apply the relevant teachings without such details. Aspects of the disclosed subject matter are not limited to the specific devices, systems, and method described because the relevant teachings can be applied or practice in a variety of ways. The terminology and nomenclature used herein is for the purpose of describing particular aspects only and is not intended to be limiting. In general, well-known instruction instances, protocols, structures, and techniques are not necessarily shown in detail. 
     The term “coupled” or “connected” as used herein refers to any logical, optical, physical, or electrical connection, including a link or the like by which the electrical or magnetic signals produced or supplied by one system element are imparted to another coupled or connected system element. Unless described otherwise, coupled or connected elements or devices are not necessarily directly connected to one another and may be separated by intermediate components, elements, or communication media, one or more of which may modify, manipulate, or carry the electrical signals. The term “on” means directly supported by an element or indirectly supported by the element through another element integrated into or supported by the element. 
     The orientations of the device and associated components and any other complete devices incorporating a camera, an inertial measurement unit, or both such as shown in any of the drawings, are given by way of example only, for illustration and discussion purposes. In operation, the eyewear device may be oriented in any other direction suitable to the particular application of the eyewear device; for example, up, down, sideways, or any other orientation. Also, to the extent used herein, any directional term, such as front, rear, inward, outward, toward, left, right, lateral, longitudinal, up, down, upper, lower, top, bottom, side, horizontal, vertical, and diagonal are used by way of example only, and are not limiting as to the direction or orientation of any camera or inertial measurement unit as constructed as otherwise described herein. 
     Additional objects, advantages and novel features of the examples will be set forth in part in the following description, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the present subject matter may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims. 
     Reference now is made in detail to the examples illustrated in the accompanying drawings and discussed below. 
       FIG.  1 A  is a side view (right) of an example hardware configuration of an eyewear device  100  which includes a touch-sensitive input device or touchpad  181 . As shown, the touchpad  181  may have a boundary that is subtle and not easily seen; alternatively, the boundary may be plainly visible or include a raised or otherwise tactile edge that provides feedback to the user about the location and boundary of the touchpad  181 . In other implementations, the eyewear device  100  may include a touchpad on the left side. 
     The surface of the touchpad  181  is configured to detect finger touches, taps, and gestures (e.g., moving touches) for use with a GUI displayed by the eyewear device, on an image display, to allow the user to navigate through and select menu options in an intuitive manner, which enhances and simplifies the user experience. 
     Detection of finger inputs on the touchpad  181  can enable several functions. For example, touching anywhere on the touchpad  181  may cause the GUI to display or highlight an item on the image display, which may be projected onto at least one of the optical assemblies  180 A,  180 B. Double tapping on the touchpad  181  may select an item or icon. Sliding or swiping a finger in a particular direction (e.g., from front to back, back to front, up to down, or down to) may cause the items or icons to slide or scroll in a particular direction; for example, to move to a next item, icon, video, image, page, or slide. Sliding the finger in another direction may slide or scroll in the opposite direction; for example, to move to a previous item, icon, video, image, page, or slide. The touchpad  181  can be virtually anywhere on the eyewear device  100 . 
     In one example, an identified finger gesture of a single tap on the touchpad  181 , initiates selection or pressing of a graphical user interface element in the image presented on the image display of the optical assembly  180 A,  180 B. An adjustment to the image presented on the image display of the optical assembly  180 A,  180 B based on the identified finger gesture can be a primary action which selects or submits the graphical user interface element on the image display of the optical assembly  180 A,  180 B for further display or execution. 
     As shown, the eyewear device  100  includes a right visible-light camera  114 B. As further described herein, two cameras  114 A,  114 B capture image information for a scene from two separate viewpoints. The two captured images may be used to project a three-dimensional display onto an image display for viewing with 3D glasses. 
     The eyewear device  100  includes a right optical assembly  180 B with an image display to present images, such as depth images. As shown in  FIGS.  1 A and  1 B , the eyewear device  100  includes the right visible-light camera  114 B. The eyewear device  100  can include multiple visible-light cameras  114 A,  114 B that form a passive type of three-dimensional camera, such as stereo camera, of which the right visible-light camera  114 B is located on a right corner  110 B. As shown in  FIGS.  1 C-D , the eyewear device  100  also includes a left visible-light camera  114 A. 
     Left and right visible-light cameras  114 A,  114 B are sensitive to the visible-light range wavelength. Each of the visible-light cameras  114 A,  114 B have a different frontward facing field of view which are overlapping to enable generation of three-dimensional depth images, for example, right visible-light camera  114 B depicts a right field of view  111 B. Generally, a “field of view” is the part of the scene that is visible through the camera at a particular position and orientation in space. The fields of view  111 A and  111 B have an overlapping field of view  304  ( FIG.  3   ). Objects or object features outside the field of view  111 A,  111 B when the visible-light camera captures the image are not recorded in a raw image (e.g., photograph or picture). The field of view describes an angle range or extent, which the image sensor of the visible-light camera  114 A,  114 B picks up electromagnetic radiation of a given scene in a captured image of the given scene. Field of view can be expressed as the angular size of the view cone; i.e., an angle of view. The angle of view can be measured horizontally, vertically, or diagonally. 
     In an example, visible-light cameras  114 A,  114 B have a field of view with an angle of view between 40° to 110°, for example approximately 100°, and have a resolution of 480×480 pixels or greater. The “angle of coverage” describes the angle range that a lens of visible-light cameras  114 A,  114 B or infrared camera  410  (see  FIG.  2 A ) can effectively image. Typically, the camera lens produces an image circle that is large enough to cover the film or sensor of the camera completely, possibly including some vignetting (e.g., a darkening of the image toward the edges when compared to the center). If the angle of coverage of the camera lens does not fill the sensor, the image circle will be visible, typically with strong vignetting toward the edge, and the effective angle of view will be limited to the angle of coverage. 
     Examples of such visible-light cameras  114 A,  114 B include a high-resolution complementary metal-oxide-semiconductor (CMOS) image sensor and a digital VGA camera (video graphics array) capable of resolutions of  640 p (e.g., 640×480 pixels for a total of 0.3 megapixels), 720 p, or 1080 p. Other examples of visible-light cameras  114 A,  114 B that can capture high-definition (HD) still images and store them at a resolution of 1642 by 1642 pixels (or greater); or record high-definition video at a high frame rate (e.g., thirty to sixty frames per second or more) and store the recording at a resolution of 1216 by 1216 pixels (or greater). 
     The eyewear device  100  may capture image sensor data from the visible-light cameras  114 A,  114 B along with geolocation data, digitized by an image processor, for storage in a memory. The visible-light cameras  114 A,  114 B capture respective left and right raw images in the two-dimensional space domain that comprise a matrix of pixels on a two-dimensional coordinate system that includes an X-axis for horizontal position and a Y-axis for vertical position. Each pixel includes a color attribute value (e.g., a red pixel light value, a green pixel light value, or a blue pixel light value); and a position attribute (e.g., an X-axis coordinate and a Y-axis coordinate). 
     In order to capture stereo images for later display as a three-dimensional projection, the image processor  412  (shown in  FIG.  4   ) may be coupled to the visible-light cameras  114 A,  114 B to receive and store the visual image information. The image processor  412 , or another processor, controls operation of the visible-light cameras  114 A,  114 B to act as a stereo camera simulating human binocular vision and may add a timestamp to each image. The timestamp on each pair of images allows display of the images together as part of a three-dimensional projection. Three-dimensional projections produce an immersive, life-like experience that is desirable in a variety of contexts, including virtual reality (VR) and video gaming. 
       FIG.  1 B  is a perspective, cross-sectional view of a right corner  110 B of the eyewear device  100  of  FIG.  1 A  depicting the right visible-light camera  114 B of the camera system, and a circuit board.  FIG.  1 C  is a side view (left) of an example hardware configuration of an eyewear device  100  of  FIG.  1 A , which shows a left visible-light camera  114 A of the camera system.  FIG.  1 D  is a perspective, cross-sectional view of a left corner  110 A of the eyewear device of  FIG.  1 C  depicting the left visible-light camera  114 A of the three-dimensional camera, and a circuit board. 
     Construction and placement of the left visible-light camera  114 A is substantially similar to the right visible-light camera  114 B, except the connections and coupling are on the left lateral side  170 A. As shown in the example of  FIG.  1 B , the eyewear device  100  includes the right visible-light camera  114 B and a circuit board  140 B, which may be a flexible printed circuit board (PCB). The right hinge  126 B connects the right corner  110 B to a right temple  125 B of the eyewear device  100 . In some examples, components of the right visible-light camera  114 B, the flexible PCB  140 B, or other electrical connectors or contacts may be located on the right temple  125 B or the right hinge  126 B. 
     The right corner  110 B includes corner body  190  and a corner cap, with the corner cap omitted in the cross-section of  FIG.  1 B . Disposed inside the right corner  110 B are various interconnected circuit boards, such as PCBs or flexible PCBs, that include controller circuits for right visible-light camera  114 B, microphone(s), low-power wireless circuitry (e.g., for wireless short range network communication via Bluetooth™), high-speed wireless circuitry (e.g., for wireless local area network communication via Wi-Fi). 
     The right visible-light camera  114 B is coupled to or disposed on the flexible PCB  140 B and covered by a visible-light camera cover lens, which is aimed through opening(s) formed in the frame  105 . For example, the right rim  107 B of the frame  105 , shown in  FIG.  2 A , is connected to the right corner  110 B and includes the opening(s) for the visible-light camera cover lens. The frame  105  includes a front side configured to face outward and away from the eye of the user. The opening for the visible-light camera cover lens is formed on and through the front or outward-facing side of the frame  105 . In the example, the right visible-light camera  114 B has an outward-facing field of view  111 B (shown in  FIG.  3   ) with a line of sight or perspective that is correlated with the right eye of the user of the eyewear device  100 . The visible-light camera cover lens can also be adhered to a front side or outward-facing surface of the right corner  110 B in which an opening is formed with an outward-facing angle of coverage, but in a different outwardly direction. The coupling can also be indirect via intervening components. 
     As shown in  FIG.  1 B , flexible PCB  140 B is disposed inside the right corner  110 B and is coupled to one or more other components housed in the right corner  110 B. Although shown as being formed on the circuit boards of the right corner  110 B, the right visible-light camera  114 B can be formed on the circuit boards of the left corner  110 A, the temples  125 A,  125 B, or the frame  105 . 
       FIGS.  2 A and  2 B  are perspective views, from the rear, of example hardware configurations of the eyewear device  100 , including two different types of image displays. The eyewear device  100  is sized and shaped in a form configured for wearing by a user; the form of eyeglasses is shown in the example. The eyewear device  100  can take other forms and may incorporate other types of frameworks; for example, a headgear, a headset, or a helmet. 
     In the eyeglasses example, eyewear device  100  includes a frame  105  including a left rim  107 A connected to a right rim  107 B via a bridge  106  adapted to be supported by a nose of the user. The left and right rims  107 A,  107 B include respective apertures  175 A,  175 B, which hold a respective optical element  180 A,  180 B, such as a lens and a display device. As used herein, the term “lens” is meant to include transparent or translucent pieces of glass or plastic having curved or flat surfaces that cause light to converge/diverge or that cause little or no convergence or divergence. 
     Although shown as having two optical elements  180 A,  180 B, the eyewear device  100  can include other arrangements, such as a single optical element (or it may not include any optical element  180 A,  180 B), depending on the application or the intended user of the eyewear device  100 . As further shown, eyewear device  100  includes a left corner  110 A adjacent the left lateral side  170 A of the frame  105  and a right corner  110 B adjacent the right lateral side  170 B of the frame  105 . The corners  110 A,  110 B may be integrated into the frame  105  on the respective sides  170 A,  170 B (as illustrated) or implemented as separate components attached to the frame  105  on the respective sides  170 A,  170 B. Alternatively, the corners  110 A,  110 B may be integrated into temples (not shown) attached to the frame  105 . 
     In one example, the image display of optical assembly  180 A,  180 B includes an integrated image display. As shown in  FIG.  2 A , each optical assembly  180 A,  180 B includes a suitable display matrix  177 , such as a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, or any other such display. Each optical assembly  180 A,  180 B also includes an optical layer or layers  176 , which can include lenses, optical coatings, prisms, mirrors, waveguides, optical strips, and other optical components in any combination. The optical layers  176 A,  176 B, . . .  176 N (shown as  176 A-N in  FIG.  2 A  and herein) can include a prism having a suitable size and configuration and including a first surface for receiving light from a display matrix and a second surface for emitting light to the eye of the user. The prism of the optical layers  176 A-N extends over all or at least a portion of the respective apertures  175 A,  175 B formed in the left and right rims  107 A,  107 B to permit the user to see the second surface of the prism when the eye of the user is viewing through the corresponding left and right rims  107 A,  107 B. The first surface of the prism of the optical layers  176 A-N faces upwardly from the frame  105  and the display matrix  177  overlies the prism so that photons and light emitted by the display matrix  177  impinge the first surface. The prism is sized and shaped so that the light is refracted within the prism and is directed toward the eye of the user by the second surface of the prism of the optical layers  176 A-N. In this regard, the second surface of the prism of the optical layers  176 A-N can be convex to direct the light toward the center of the eye. The prism can optionally be sized and shaped to magnify the image projected by the display matrix  177 , and the light travels through the prism so that the image viewed from the second surface is larger in one or more dimensions than the image emitted from the display matrix  177 . 
     In one example, the optical layers  176 A-N may include an LCD layer that is transparent (keeping the lens open) unless and until a voltage is applied which makes the layer opaque (closing or blocking the lens). The image processor  412  on the eyewear device  100  may execute programming to apply the voltage to the LCD layer in order to produce an active shutter system, making the eyewear device  100  suitable for viewing visual content when displayed as a three-dimensional projection. Technologies other than LCD may be used for the active shutter mode, including other types of reactive layers that are responsive to a voltage or another type of input. 
     In another example, the image display device of optical assembly  180 A,  180 B includes a projection image display as shown in  FIG.  2 B . Each optical assembly  180 A,  180 B includes a laser projector  150 , which is a three-color laser projector using a scanning mirror or galvanometer. During operation, an optical source such as a laser projector  150  is disposed in or on one of the temples  125 A,  125 B of the eyewear device  100 . Optical assembly  180 B in this example includes one or more optical strips  155 A,  155 B, . . .  155 N (shown as  155 A-N in  FIG.  2 B ) which are spaced apart and across the width of the lens of each optical assembly  180 A,  180 B or across a depth of the lens between the front surface and the rear surface of the lens. 
     As the photons projected by the laser projector  150  travel across the lens of each optical assembly  180 A,  180 B, the photons encounter the optical strips  155 A-N. When a particular photon encounters a particular optical strip, the photon is either redirected toward the user&#39;s eye, or it passes to the next optical strip. A combination of modulation of laser projector  150 , and modulation of optical strips, may control specific photons or beams of light. In an example, a processor controls optical strips  155 A-N by initiating mechanical, acoustic, or electromagnetic signals. Although shown as having two optical assemblies  180 A,  180 B, the eyewear device  100  can include other arrangements, such as a single or three optical assemblies, or each optical assembly  180 A,  180 B may have arranged different arrangement depending on the application or intended user of the eyewear device  100 . 
     As further shown in  FIGS.  2 A and  2 B , eyewear device  100  includes a left corner  110 A adjacent the left lateral side  170 A of the frame  105  and a right corner  110 B adjacent the right lateral side  170 B of the frame  105 . The corners  110 A,  110 B may be integrated into the frame  105  on the respective lateral sides  170 A,  170 B (as illustrated) or implemented as separate components attached to the frame  105  on the respective sides  170 A,  170 B. Alternatively, the corners  110 A,  110 B may be integrated into temples  125 A,  125 B attached to the frame  105 . 
     In another example, the eyewear device  100  shown in  FIG.  2 B  may include two projectors, a left projector  150 A (not shown) and a right projector  150 B (shown as projector  150 ). The left optical assembly  180 A may include a left display matrix  177 A (not shown) or a left set of optical strips  155 ′A,  155 ′B, . . .  155 ′N ( 155  prime, A through N, not shown) which are configured to interact with light from the left projector  150 A. Similarly, the right optical assembly  180 B may include a right display matrix  177 B (not shown) or a right set of optical strips  155 ″A,  155 ″B, . . .  155 ″N ( 155  double prime, A through N, not shown) which are configured to interact with light from the right projector  150 B. In this example, the eyewear device  100  includes a left display and a right display. 
       FIG.  3    is a diagrammatic depiction of a three-dimensional scene  306 , a left raw image  302 A captured by a left visible-light camera  114 A, and a right raw image  302 B captured by a right visible-light camera  114 B. The left field of view  111 A may overlap, as shown, with the right field of view  111 B. The overlapping field of view  304  represents that portion of the image captured by both cameras  114 A,  114 B. The term ‘overlapping’ when referring to field of view means the matrix of pixels in the generated raw images overlap by thirty percent (30%) or more. ‘Substantially overlapping’ means the matrix of pixels in the generated raw images—or in the infrared image of scene—overlap by fifty percent (50%) or more. As described herein, the two raw images  302 A,  302 B may be processed to include a timestamp, which allows the images to be displayed together as part of a three-dimensional projection. 
     For the capture of stereo images, as illustrated in  FIG.  3   , a pair of raw red, green, and blue (RGB) images are captured of a real scene  306  at a given moment in time—a left raw image  302 A captured by the left camera  114 A and right raw image  302 B captured by the right camera  114 B. When the pair of raw images  302 A,  302 B are processed (e.g., by the image processor  412 ), depth images are generated. The generated depth images may be viewed on an optical assembly  180 A,  180 B of an eyewear device, on another display (e.g., the image display  580  on a mobile device  401 ), or on a screen. 
     The generated depth images are in the three-dimensional space domain and can comprise a matrix of vertices on a three-dimensional location coordinate system that includes an X axis for horizontal position (e.g., length), a Y axis for vertical position (e.g., height), and a Z axis for depth (e.g., distance). Each vertex may include a color attribute (e.g., a red pixel light value, a green pixel light value, or a blue pixel light value); a position attribute (e.g., an X location coordinate, a Y location coordinate, and a Z location coordinate); a texture attribute; a reflectance attribute; or a combination thereof. The texture attribute quantifies the perceived texture of the depth image, such as the spatial arrangement of color or intensities in a region of vertices of the depth image. 
     In one example, the interactive augmented reality system  400  ( FIG.  4   ) includes the eyewear device  100 , which includes a frame  105  and a left temple  110 A extending from a left lateral side  170 A of the frame  105  and a right temple  125 B extending from a right lateral side  170 B of the frame  105 . The eyewear device  100  may further include at least two visible-light cameras  114 A,  114 B having overlapping fields of view. In one example, the eyewear device  100  includes a left visible-light camera  114 A with a left field of view  111 A, as illustrated in  FIG.  3   . The left camera  114 A is connected to the frame  105  or the left temple  110 A to capture a left raw image  302 A from the left side of scene  306 . The eyewear device  100  further includes a right visible-light camera  114 B with a right field of view  111 B. The right camera  114 B is connected to the frame  105  or the right temple  125 B to capture a right raw image  302 B from the right side of scene  306 . 
       FIG.  4    is a functional block diagram of an example interactive augmented reality system  400  that includes a wearable device (e.g., an eyewear device  100 ), a mobile device  401 , and a server system  498  connected via various networks  495  such as the Internet. The interactive augmented reality system  400  includes a low-power wireless connection  425  and a high-speed wireless connection  437  between the eyewear device  100  and the mobile device  401 . 
     As shown in  FIG.  4   , the eyewear device  100  includes one or more visible-light cameras  114 A,  114 B that capture still images, video images, or both still and video images, as described herein. The cameras  114 A,  114 B may have a direct memory access (DMA) to high-speed circuitry  430  and function as a stereo camera. The cameras  114 A,  114 B may be used to capture initial-depth images that may be rendered into three-dimensional (3D) models that are texture-mapped images of a red, green, and blue (RGB) imaged scene. The device  100  may also include a depth sensor  213 , which uses infrared signals to estimate the position of objects relative to the device  100 . The depth sensor  213  in some examples includes one or more infrared emitter(s)  215  and infrared camera(s)  410 . 
     The eyewear device  100  further includes two image displays of each optical assembly  180 A,  180 B (one associated with the left side  170 A and one associated with the right side  170 B). The eyewear device  100  also includes an image display driver  442 , an image processor  412 , low-power circuitry  420 , and high-speed circuitry  430 . The image displays of each optical assembly  180 A,  180 B are for presenting images, including still images, video images, or still and video images. The image display driver  442  is coupled to the image displays of each optical assembly  180 A,  180 B in order to control the display of images. 
     The eyewear device  100  additionally includes one or more speakers  440  (e.g., one associated with the left side of the eyewear device and another associated with the right side of the eyewear device). The speakers  440  may be incorporated into the frame  105 , temples  125 , or corners  110  of the eyewear device  100 . The one or more speakers  440  are driven by audio processor  443  under control of low-power circuitry  420 , high-speed circuitry  430 , or both. The speakers  440  are for presenting audio signals including, for example, a beat track. The audio processor  443  is coupled to the speakers  440  in order to control the presentation of sound. 
     The components shown in  FIG.  4    for the eyewear device  100  are located on one or more circuit boards, for example a printed circuit board (PCB) or flexible printed circuit (FPC), located in the rims or temples. Alternatively, or additionally, the depicted components can be located in the corners, frames, hinges, or bridge of the eyewear device  100 . Left and right visible-light cameras  114 A,  114 B can include digital camera elements such as a complementary metal-oxide-semiconductor (CMOS) image sensor, a charge-coupled device, a lens, or any other respective visible or light capturing elements that may be used to capture data, including still images or video of scenes with unknown objects. 
     As shown in  FIG.  4   , high-speed circuitry  430  includes a high-speed processor  432 , a memory  434 , and high-speed wireless circuitry  436 . In the example, the image display driver  442  is coupled to the high-speed circuitry  430  and operated by the high-speed processor  432  in order to drive the left and right image displays of each optical assembly  180 A,  180 B. High-speed processor  432  may be any processor capable of managing high-speed communications and operation of any general computing system needed for eyewear device  100 . High-speed processor  432  includes processing resources needed for managing high-speed data transfers on high-speed wireless connection  437  to a wireless local area network (WLAN) using high-speed wireless circuitry  436 . 
     In some examples, the high-speed processor  432  executes an operating system such as a LINUX operating system or other such operating system of the eyewear device  100  and the operating system is stored in memory  434  for execution. In addition to any other responsibilities, the high-speed processor  432  executes a software architecture for the eyewear device  100  that is used to manage data transfers with high-speed wireless circuitry  436 . In some examples, high-speed wireless circuitry  436  is configured to implement Institute of Electrical and Electronic Engineers (IEEE) 802.11 communication standards, also referred to herein as Wi-Fi. In other examples, other high-speed communications standards may be implemented by high-speed wireless circuitry  436 . 
     The low-power circuitry  420  includes a low-power processor  422  and low-power wireless circuitry  424 . The low-power wireless circuitry  424  and the high-speed wireless circuitry  436  of the eyewear device  100  can include short-range transceivers (Bluetooth™ or Bluetooth Low-Energy (BLE)) and wireless wide, local, or wide-area network transceivers (e.g., cellular or Wi-Fi). Mobile device  401 , including the transceivers communicating via the low-power wireless connection  425  and the high-speed wireless connection  437 , may be implemented using details of the architecture of the eyewear device  100 , as can other elements of the network  495 . 
     Memory  434  includes any storage device capable of storing various data and applications, including, among other things, camera data generated by the left and right visible-light cameras  114 A,  114 B, the infrared camera(s)  410 , the image processor  412 , and images generated for display by the image display driver  442  on the image display of each optical assembly  180 A,  180 B. Although the memory  434  is shown as integrated with high-speed circuitry  430 , the memory  434  in other examples may be an independent, standalone element of the eyewear device  100 . In certain such examples, electrical routing lines may provide a connection through a chip that includes the high-speed processor  432  from the image processor  412  or low-power processor  422  to the memory  434 . In other examples, the high-speed processor  432  may manage addressing of memory  434  such that the low-power processor  422  will boot the high-speed processor  432  any time that a read or write operation involving memory  434  is needed. 
     As shown in  FIG.  4   , the high-speed processor  432  of the eyewear device  100  can be coupled to the camera system (visible-light cameras  114 A,  114 B), the image display driver  442 , the user input device  491 , and the memory  434 . As shown in  FIG.  5   , the CPU  540  of the mobile device  401  may be coupled to a camera system  570 , a mobile display driver  582 , a user input layer  591 , and a memory  540 A. 
     The server system  498  may be one or more computing devices as part of a service or network computing system, for example, that include a processor, a memory, and network communication interface to communicate over the network  495  with an eyewear device  100  and a mobile device  401 . 
     The output components of the eyewear device  100  include visual elements, such as the left and right image displays associated with each lens or optical assembly  180 A,  180 B as described in  FIGS.  2 A and  2 B  (e.g., a display such as a liquid crystal display (LCD), a plasma display panel (PDP), a light emitting diode (LED) display, a projector, or a waveguide). The eyewear device  100  may include a user-facing indicator (e.g., an LED, a loudspeaker, or a vibrating actuator), or an outward-facing signal (e.g., an LED, a loudspeaker). The image displays of each optical assembly  180 A,  180 B are driven by the image display driver  442 . In some example configurations, the output components of the eyewear device  100  further include additional indicators such as audible elements (e.g., loudspeakers), tactile components (e.g., an actuator such as a vibratory motor to generate haptic feedback), and other signal generators. For example, the device  100  may include a user-facing set of indicators, and an outward-facing set of signals. The user-facing set of indicators are configured to be seen or otherwise sensed by the user of the device  100 . For example, the device  100  may include an LED display positioned so the user can see it, a one or more speakers positioned to generate a sound the user can hear, or an actuator to provide haptic feedback the user can feel. The outward-facing set of signals are configured to be seen or otherwise sensed by an observer near the device  100 . Similarly, the device  100  may include an LED, a loudspeaker, or an actuator that is configured and positioned to be sensed by an observer. 
     The input components of the eyewear device  100  may include alphanumeric input components (e.g., a touch screen or touchpad configured to receive alphanumeric input, a photo-optical keyboard, or other alphanumeric-configured elements), pointer-based input components (e.g., a mouse, a touchpad, a trackball, a joystick, a motion sensor, or other pointing instruments), tactile input components (e.g., a button switch, a touch screen or touchpad that senses the location, force or location and force of touches or touch gestures, or other tactile-configured elements), and audio input components (e.g., a microphone), and the like. The mobile device  401  and the server system  498  may include alphanumeric, pointer-based, tactile, audio, and other input components. 
     In some examples, the eyewear device  100  includes a collection of motion-sensing components referred to as an inertial measurement unit  472 . The motion-sensing components may be micro-electro-mechanical systems (MEMS) with microscopic moving parts, often small enough to be part of a microchip. The inertial measurement unit (IMU)  472  in some example configurations includes an accelerometer, a gyroscope, and a magnetometer. The accelerometer senses the linear acceleration of the device  100  (including the acceleration due to gravity) relative to three orthogonal axes (x, y, z). The gyroscope senses the angular velocity of the device  100  about three axes of rotation (pitch, roll, yaw). Together, the accelerometer and gyroscope can provide position, orientation, and motion data about the device relative to six axes (x, y, z, pitch, roll, yaw). The magnetometer, if present, senses the heading of the device  100  relative to magnetic north. The position of the device  100  may be determined by location sensors, such as a GPS unit  473 , one or more transceivers to generate relative position coordinates, altitude sensors or barometers, and other orientation sensors. Such positioning system coordinates can also be received over the wireless connections  425 ,  437  from the mobile device  401  via the low-power wireless circuitry  424  or the high-speed wireless circuitry  436 . 
     The IMU  472  may include or cooperate with a digital motion processor or programming that gathers the raw data from the components and computes a number of useful values about the position, orientation, and motion of the device  100 . For example, the acceleration data gathered from the accelerometer can be integrated to obtain the velocity relative to each axis (x, y, z); and integrated again to obtain the position of the device  100  (in linear coordinates, x, y, and z). The angular velocity data from the gyroscope can be integrated to obtain the position of the device  100  (in spherical coordinates). The programming for computing these useful values may be stored in memory  434  and executed by the high-speed processor  432  of the eyewear device  100 . 
     The eyewear device  100  may optionally include additional peripheral sensors, such as biometric sensors, specialty sensors, or display elements integrated with eyewear device  100 . For example, peripheral device elements may include any I/O components including output components, motion components, position components, or any other such elements described herein. For example, the biometric sensors may include components to detect expressions (e.g., hand expressions, facial expressions, vocal expressions, body gestures, or eye tracking), to measure bio signals (e.g., blood pressure, heart rate, body temperature, perspiration, or brain waves), or to identify a person (e.g., identification based on voice, retina, facial characteristics, fingerprints, or electrical bio signals such as electroencephalogram data), and the like. 
     The mobile device  401  may be a smartphone, tablet, laptop computer, access point, or any other such device capable of connecting with eyewear device  100  using both a low-power wireless connection  425  and a high-speed wireless connection  437 . Mobile device  401  is connected to server system  498  and network  495 . The network  495  may include any combination of wired and wireless connections. 
     The interactive augmented reality system  400 , as shown in  FIG.  4   , includes a computing device, such as mobile device  401 , coupled to an eyewear device  100  over a network. The interactive augmented reality system  400  includes a memory for storing instructions and a processor for executing the instructions. Execution of the instructions of the interactive augmented reality system  400  by the processor  432  configures the eyewear device  100  to cooperate with the mobile device  401 . The interactive augmented reality system  400  may utilize the memory  434  of the eyewear device  100  or the memory elements  540 A,  540 B,  540 C of the mobile device  401  ( FIG.  5   ). Also, the interactive augmented reality system  400  may utilize the processor elements  432 ,  422  of the eyewear device  100  or the central processing unit (CPU)  540  of the mobile device  401  ( FIG.  5   ). In addition, the interactive augmented reality system  400  may further utilize the memory and processor elements of the server system  498 . In this aspect, the memory and processing functions of the interactive augmented reality system  400  can be shared or distributed across the eyewear device  100 , the mobile device  401 , and the server system  498 . 
     The memory  434  includes song files  482  and virtual objects  484 . The song files  482  includes a tempo (e.g., beat track) and, optionally, a sequence of notes and note values. A note is a symbol denoting a particular pitch or other musical sound. The note value includes the duration the note is played, relative to the tempo, and may include other qualities such as loudness, emphasis, articulation, and phrasing relative to other notes. The tempo, in some implementations, includes a default value along with a user interface through which the user may select a particular tempo for use during playback of the song. The virtual objects  484  include image data for identifying objects or features in images captured by the cameras  114 . The objects may be physical features such as known paintings or physical markers for use in localizing the eyewear device  100  within an environment. 
     The memory  434  additionally includes, for execution by the processor  432 , a position detection utility  460 , a marker registration utility  462 , a localization utility  464 , a virtual object rendering utility  466 , a physics engine  468 , and a prediction engine  470 . The position detection utility  460  configures the processor  432  to determine the position (location and orientation) within an environment, e.g., using the localization utility  464 . The marker registration utility  462  configures the processor  432  to register markers within the environment. The markers may be predefined physical markers having a known location within an environment or assigned by the processor  432  to a particular location with respect to the environment within which the eyewear device  100  is operating or with respect to the eyewear itself. The localization utility  464  configures the processor  432  to obtain localization data for use in determining the position of the eyewear device  100 , virtual objects presented by the eyewear device, or a combination thereof. The location data may be derived from a series of images, an IMU unit  472 , a GPS unit  473 , or a combination thereof. The virtual object rendering utility  466  configures the processor  432  to render virtual images for display by the image display  180  under control of the image display driver  442  and the image processor  412 . The physics engine  468  configures the processor  432  to apply laws of physics such as gravity and friction to the virtual word, e.g., between virtual game pieces. The prediction engine  470  configures the processor  432  to predict anticipated movement of an object such as the eyewear device  100  based on its current heading, input from sensors such as the IMU  472 , images of the environment, or a combination thereof. 
       FIG.  5    is a high-level functional block diagram of an example mobile device  401 . Mobile device  401  includes a flash memory  540 A which stores programming to be executed by the CPU  540  to perform all or a subset of the functions described herein. 
     The mobile device  401  may include a camera  570  that comprises at least two visible-light cameras (first and second visible-light cameras with overlapping fields of view) or at least one visible-light camera and a depth sensor with substantially overlapping fields of view. Flash memory  540 A may further include multiple images or video, which are generated via the camera  570 . 
     As shown, the mobile device  401  includes an image display  580 , a mobile display driver  582  to control the image display  580 , and a display controller  584 . In the example of  FIG.  5   , the image display  580  includes a user input layer  591  (e.g., a touchscreen) that is layered on top of or otherwise integrated into the screen used by the image display  580 . 
     Examples of touchscreen-type mobile devices that may be used include (but are not limited to) a smart phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or other portable device. However, the structure and operation of the touchscreen-type devices is provided by way of example; the subject technology as described herein is not intended to be limited thereto. For purposes of this discussion,  FIG.  5    therefore provides a block diagram illustration of the example mobile device  401  with a user interface that includes a touchscreen input layer  591  for receiving input (by touch, multi-touch, or gesture, and the like, by hand, stylus, or other tool) and an image display  580  for displaying content 
     As shown in  FIG.  5   , the mobile device  401  includes at least one digital transceiver (XCVR)  510 , shown as WWAN XCVRs, for digital wireless communications via a wide-area wireless mobile communication network. The mobile device  401  also includes additional digital or analog transceivers, such as short-range transceivers (XCVRs)  520  for short-range network communication, such as via NFC, VLC, DECT, ZigBee, Bluetooth™, or Wi-Fi. For example, short range XCVRs  520  may take the form of any available two-way wireless local area network (WLAN) transceiver of a type that is compatible with one or more standard protocols of communication implemented in wireless local area networks, such as one of the Wi-Fi standards under IEEE 802.11. 
     To generate location coordinates for positioning of the mobile device  401 , the mobile device  401  can include a global positioning system (GPS) receiver. Alternatively, or additionally the mobile device  401  can utilize either or both the short range XCVRs  520  and WWAN XCVRs  510  for generating location coordinates for positioning. For example, cellular network, Wi-Fi, or Bluetooth™ based positioning systems can generate very accurate location coordinates, particularly when used in combination. Such location coordinates can be transmitted to the eyewear device over one or more network connections via XCVRs  510 ,  520 . 
     The transceivers  510 ,  520  (i.e., the network communication interface) conforms to one or more of the various digital wireless communication standards utilized by modern mobile networks. Examples of WWAN transceivers  510  include (but are not limited to) transceivers configured to operate in accordance with Code Division Multiple Access (CDMA) and 3rd Generation Partnership Project (3GPP) network technologies including, for example and without limitation, 3GPP type 2 (or 3GPP2) and LTE, at times referred to as “4G.” For example, the transceivers  510 ,  520  provide two-way wireless communication of information including digitized audio signals, still image and video signals, web page information for display as well as web-related inputs, and various types of mobile message communications to/from the mobile device  401 . 
     The mobile device  401  further includes a microprocessor that functions as a central processing unit (CPU); shown as CPU  540  in  FIG.  4   . A processor is a circuit having elements structured and arranged to perform one or more processing functions, typically various data processing functions. Although discrete logic components could be used, the examples utilize components forming a programmable CPU. A microprocessor for example includes one or more integrated circuit (IC) chips incorporating the electronic elements to perform the functions of the CPU. The CPU  540 , for example, may be based on any known or available microprocessor architecture, such as a Reduced Instruction Set Computing (RISC) using an ARM architecture, as commonly used today in mobile devices and other portable electronic devices. Of course, other arrangements of processor circuitry may be used to form the CPU  540  or processor hardware in smartphone, laptop computer, and tablet. 
     The CPU  540  serves as a programmable host controller for the mobile device  401  by configuring the mobile device  401  to perform various operations, for example, in accordance with instructions or programming executable by CPU  540 . For example, such operations may include various general operations of the mobile device, as well as operations related to the programming for applications on the mobile device. Although a processor may be configured by use of hardwired logic, typical processors in mobile devices are general processing circuits configured by execution of programming. 
     The mobile device  401  includes a memory or storage system, for storing programming and data. In the example, the memory system may include a flash memory  540 A, a random-access memory (RAM)  540 B, and other memory components  540 C, as needed. The RAM  540 B serves as short-term storage for instructions and data being handled by the CPU  540 , e.g., as a working data processing memory. The flash memory  540 A typically provides longer-term storage. 
     Hence, in the example of mobile device  401 , the flash memory  540 A is used to store programming or instructions for execution by the CPU  540 . Depending on the type of device, the mobile device  401  stores and runs a mobile operating system through which specific applications are executed. Examples of mobile operating systems include Google Android, Apple iOS (for iPhone or iPad devices), Windows Mobile, Amazon Fire OS, RIM BlackBerry OS, or the like. 
     The processor  432  within the eyewear device  100  constructs a map of the environment surrounding the eyewear device  100 , determines a location of the eyewear device within the mapped environment, and determines a relative position of the eyewear device to one or more objects in the mapped environment. In one example, the processor  432  constructs the map and determines location and position information using a simultaneous localization and mapping (SLAM) algorithm applied to data received from one or more sensors. In the context of augmented reality, a SLAM algorithm is used to construct and update a map of an environment, while simultaneously tracking and updating the location of a device (or a user) within the mapped environment. The mathematical solution can be approximated using various statistical methods, such as particle filters, Kalman filters, extended Kalman filters, and covariance intersection. 
     Sensor data includes images received from one or both of the cameras  114 A,  114 B, distance(s) received from a laser range finder, position information received from a GPS unit  473 , or a combination of two or more of such sensor data, or from other sensors providing data useful in determining positional information. 
       FIG.  6    depicts an example environment  600  along with elements that are useful for natural feature tracking (NFT; e.g., a tracking application using a SLAM algorithm). A user  602  of the eyewear device  100  is present in an example physical environment  600  (which, in  FIG.  6   , is an interior room). The processor  432  of the eyewear device  100  determines its position with respect to one or more objects  604  within the environment  600  using captured images, constructs a map of the environment  600  using a coordinate system (x, y, z) for the environment  600 , and determines its position within the coordinate system. Additionally, the processor  432  determines a head pose (roll, pitch, and yaw) of the eyewear device  100  within the environment by using two or more location points (e.g., three location points  606   a ,  606   b , and  606   c ) associated with a single object  604   a , or by using one or more location points  606  associated with two or more objects  604   a ,  604   b ,  604   c . In one example, the processor  432  of the eyewear device  100  positions a virtual object  408  (such as the key shown in  FIG.  6   ) within the environment  600  for augmented reality viewing via image displays  180 . 
       FIG.  7    is a flow chart  700  depicting a method for visual-inertial tracking on a wearable device (e.g., an eyewear device) having a first rolling shutter camera described herein. Although the steps are described with reference to the eyewear device  100 , as described herein, other implementations of the steps described, for other types of devices, will be understood by one of skill in the art from the description herein. Additionally, it is contemplated that one or more of the steps shown in  FIG.  7   , and in other figures, and described herein may be omitted, performed simultaneously or in a series, performed in an order other than illustrated and described, or performed in conjunction with additional steps. 
     At block  702 , the eyewear device  100  captures one or more input images of a physical environment  600  near the eyewear device  100 . The processor  432  may continuously receive input images from the visible light camera(s)  114  and store those images in memory  434  for processing. Additionally, the eyewear device  100  may capture information from other sensors (e.g., location information from a GPS unit  473 , orientation information from an IMU  472 , or distance information from a depth sensor). 
     At block  704 , the eyewear device  100  compares objects in the captured images to objects stored in a library of images to identify a match. In some implementations, the processor  432  stores the captured images in memory  434 . A library of images of known objects is stored in a virtual object database  484 . 
     In one example, the processor  432  is programmed to identify a predefined particular object (e.g., a particular picture  604   a  hanging in a known location on a wall, a window  604   b  in another wall, or an object such as a safe  604   c  positioned on the floor). Other sensor data, such as GPS data, may be used to narrow down the number of known objects for use in the comparison (e.g., only images associated with a room identified through GPS coordinates). In another example, the processor  432  is programmed to identify predefined general objects (such as one or more trees within a park). 
     At block  706 , the eyewear device  100  determines its position with respect to the object(s). The processor  432  may determine its position with respect to the objects by comparing and processing distances between two or more points in the captured images (e.g., between two or more location points on one objects  604  or between a location point  606  on each of two objects  604 ) to known distances between corresponding points in the identified objects. Distances between the points of the captured images greater than the points of the identified objects indicates the eyewear device  100  is closer to the identified object than the imager that captured the image including the identified object. On the other hand, distances between the points of the captured images less than the points of the identified objects indicates the eyewear device  100  is further from the identified object than the imager that captured the image including the identified object. By processing the relative distances, the processor  432  is able to determine the position with respect to the objects(s). Alternatively, or additionally, other sensor information, such as laser distance sensor information, may be used to determine position with respect to the object(s). 
     At block  708 , the eyewear device  100  constructs a map of an environment  600  surrounding the eyewear device  100  and determines its location within the environment. In one example, where the identified object (block  704 ) has a predefined coordinate system (x, y, z), the processor  432  of the eyewear device  100  constructs the map using that predefined coordinate system and determines its position within that coordinate system based on the determined positions (block  706 ) with respect to the identified objects. In another example, the eyewear device constructs a map using images of permanent or semi-permanent objects  604  within an environment (e.g., a tree or a park bench within a park). In accordance with this example, the eyewear device  100  may define the coordinate system (x′, y′, z′) used for the environment. 
     At block  710 , the eyewear device  100  determines a head pose (roll, pitch, and yaw) of the eyewear device  100  within the environment. The processor  432  determines head pose by using two or more location points (e.g., three location points  606   a ,  606   b , and  606   c ) on one or more objects  604  or by using one or more location points  606  on two or more objects  604 . Using conventional image processing algorithms, the processor  432  determines roll, pitch, and yaw by comparing the angle and length of a line extending between the location points for the captured images and the known images. 
     At block  712 , the eyewear device  100  presents visual images to the user. The processor  432  presents images to the user on the image displays  180  using the image processor  412  and the image display driver  442 . The processor develops and presents the visual images via the image displays responsive to the location of the eyewear device  100  within the environment  600 . 
     At block  714 , the steps described above with reference to blocks  706 - 712  are repeated to update the position of the eyewear device  100  and what is viewed by the user  602  as the user moves through the environment  600 . 
     Referring again to  FIG.  6   , the method of implementing augmented reality virtual guidance applications described herein, in this example, includes virtual markers (e.g., virtual marker  610   a ) associated with physical objects (e.g., painting  604   a ) and virtual markers associated with virtual objects (e.g., key  608 ). In one example, an eyewear device  100  uses the markers associated with physical objects to determine the position of the eyewear device  100  within an environment and uses the markers associated with virtual objects to generate overlay images presenting the associated virtual object(s)  608  in the environment  600  at the virtual marker position on the display of the eyewear device  100 . For example, markers are registered at locations in the environment for use in tracking and updating the location of users, devices, and objects (virtual and physical) in a mapped environment. Markers are sometimes registered to a high-contrast physical object, such as the relatively dark object  604   a  mounted on a lighter-colored wall, to assist cameras and other sensors with the task of detecting the marker. The markers may be preassigned or may be assigned by the eyewear device  100  upon entering the environment. Markers are also registered at locations in the environment for use in presenting virtual images at those locations in the mapped environment. 
     Markers can be encoded with or otherwise linked to information. A marker might include position information, a physical code (such as a bar code or a QR code; either visible to the user or hidden), or a combination thereof. A set of data associated with the marker is stored in the memory  434  of the eyewear device  100 . The set of data includes information about the marker  610 a, the marker&#39;s position (location and orientation), one or more virtual objects, or a combination thereof. The marker position may include three-dimensional coordinates for one or more marker landmarks  616   a , such as the corner of the generally rectangular marker  610   a  shown in  FIG.  6   . The marker location may be expressed relative to real-world geographic coordinates, a system of marker coordinates, a position of the eyewear device  100 , or other coordinate system. The one or more virtual objects associated with the marker  610   a  may include any of a variety of material, including still images, video, audio, tactile feedback, executable applications, interactive user interfaces and experiences, and combinations or sequences of such material. Any type of content capable of being stored in a memory and retrieved when the marker  610   a  is encountered or associated with an assigned marker may be classified as a virtual object in this context. The key  608  shown in  FIG.  6   , for example, is a virtual object displayed as a still image, either 2D or 3D, at a marker location. 
     In one example, the marker  610   a  may be registered in memory as being located near and associated with a physical object  604   a  (e.g., the framed work of art shown in  FIG.  6   ). In another example, the marker may be registered in memory as being a particular position with respect to the eyewear device  100 . 
       FIG.  8 A  is a flow chart  800  depicting a method for visual-inertial tracking on eyewear device  100  that uses a camera system comprising a first rolling shutter camera. At block  802 , the eyewear device  100  obtains an initial head pose for the first rolling shutter camera by determining head pose (roll, pitch, and yaw) of the eyewear device  100  within the environment. In some examples the pose is stored by processor  432  in memory, e.g., memory  434 . In one example, the processor  432  stores the pose in a look-up table in memory  434 . The processor  432  may set up the look-up table in memory and maintain the look-up table during a visual-inertial tracking process by eyewear device  100 . The look-up table includes an entry corresponding to each line of an image captured by at least one rolling shutter camera (or, for example, an entry for each line having a different pose than a preceding line due to camera motion), with the first pose stored in the first line of the look-up table. 
     At block  804 , the eyewear device  100  captures, during a capture period, an image of an environment using the first rolling shutter camera. The image includes feature points and each feature point is captured at a particular time during a capture period. The processor  432  continuously receives input images from at least one visible light camera  114  and stores those images in memory  434  for processing. In some examples, the eyewear device  100  may compare objects in the captured images to objects stored in a library of images to identify a match, e.g., for use in determining the position of the eyewear device through visual-inertial tracking (described below). A library of images of known objects is stored in a virtual object database  484  for comparison. 
     At block  806 , the eyewear device  100  senses movement of the mobile device during the capture period by obtaining motion information from the physical environment  600  near the device  100  from various sensors, for example, location or position information from a GPS unit  473 , motion or orientation information from an IMU  472  or distance information from a laser distance sensor or a combination thereof. In an example, processor  432  retrieves sensed parameters from at least one of the sensors. The processor  432  then determines motion and position information from the sensed parameters using techniques described herein. 
     At block  808 , the eyewear device  100  computes a number of poses for the first rolling shutter camera. The number of poses to computed by the rolling shutter camera is responsive to the sensed motion of the eyewear device such that relatively fewer poses are computed when the eyewear device is moving slowly (e.g., determined based on input from a motion sensor) and relatively more poses are computed when the eyewear device is moving faster. In one example, the number of poses is selected based on predefined thresholds. In accordance with this example, when the eyewear device is moving at a rate at or below a first predefined threshold (e.g., at or below 1 foot per second), the eyewear device computes a relatively low number of poses (e.g., 3 or less) per rolling shutter cycle; when the eyewear device is moving at a rate between the first predefined threshold (e.g., above 1 foot per second) and a second predefined threshold (e.g., below 3 feet per second), the eyewear device computes a medium number of poses (e.g., 4-6) per rolling shutter cycle; and when the eyewear device is moving at a rate at or above the second predefined threshold (e.g., at or above 3 feet per second), the eyewear device computes a relatively high number of poses (e.g., 7 or more) per rolling shutter cycle. By adjusting the number of poses calculated responsive to movement of the eyewear device, processing resources can be conserved when they are not necessary to produce acceptable results. 
     To calculate each of the number of poses, the processor  432 , determines an initial pose of the eyewear device  100  within the environment and obtains movement information provided by sensor input (see block  806 ) to compute a computed pose. Each computed pose corresponds to a particular time within a capture period. In one example, the processor  432  determines the pose for a line using a simultaneous localization and mapping (SLAM) algorithm applied to data received from one or more sensors for a first pose during exposure of a first line of at least one of the rolling shutter cameras. In some examples each of the computed poses is stored by processor  432  in memory, e.g., memory  434 . In one example, the processor  432  stores each of the computed poses in a look-up table in memory  434 . 
     In some examples, for each feature point in the image, the one of the number of computed poses is retrieved from the lookup table with the corresponding particular time that is closest to the corresponding particular computed time. In other examples, for each feature point in the image, the one of the number of computed poses is retrieved from the lookup table with the corresponding particular time that is immediately prior to the corresponding particular computed time. 
     In one example, where the number of poses comprises first and second calculated poses, the processor  432  stores, in a first position of a look-up table, the first calculated pose for a first line of the rolling shutter camera and, if the second calculated pose is calculated for a subsequent line of the first rolling shutter camera, the first calculated pose for the second line of the first rolling shutter camera. In one example, the number of computed poses is less than the number of feature points. 
     At block  810 , the eyewear device selects, for each feature point in the image, one of the number of computed poses by matching the particular capture time for the feature point to the particular computed time for the computed pose. At block  812 , the eyewear device determines a position of the mobile device within the environment using the feature points and the selected computed poses for the feature points. In one example, the position of the mobile device is determined by using the retrieved lookup table position poses. The first lookup table position pose for a first feature point corresponding to the first line and the second lookup table position pose for a second feature point corresponding to the second line are retrieved from memory  434 . In one example, determining the position comprises applying a simultaneous localization and mapping (SLAM) algorithm using the feature points and the selected computed poses for the feature points. 
       FIGS.  8 B- 8 D  are additional flow charts  820 ,  830 , and  840  listing steps in example methods of augmented reality guidance experiences. Although the steps are described with reference to the eyewear device  100 , as described herein, other implementations of the steps described, for other types of wearable mobile devices, will be understood by one of skill in the art from the description herein. Additionally, it is contemplated that one or more of the steps shown in  FIGS.  8 B-D , and described herein, may be omitted, performed simultaneously or in a series, performed in an order other than illustrated and described, or performed in conjunction with additional steps. 
     In  FIG.  8 B , at block  822 , the processor  432  stores each of the computed poses in a lookup table in memory  434 . At block  824 , for each feature point in the image, one of the number of the computed poses is retrieved from the lookup table with the corresponding particular time that is closest to the corresponding particular computed time. 
     In  FIG.  8 C , at block  832 , the processor  432  stores each of the computed poses in a lookup table in memory  434 . At block  834 , for each feature point in the image, one of the number of the computed poses is retrieved from the lookup table with the corresponding particular time that is immediately prior to the corresponding particular computed time. 
       FIG.  8 D  is a flow chart  840  depicting a method for visual-inertial tracking on eyewear device  100  that uses a camera system comprising first and second rolling shutter cameras. In one example, the camera system is a stereoscopic camera system.  FIG.  8 A  illustrates steps  802  through  812  performed for a first rolling shutter camera. The steps performed for the second rolling shutter camera are as follows. 
     At step  842 , the eyewear device  100  obtains an initial pose for the second rolling shutter camera. In some examples the pose is stored by processor  432  in memory, e.g., memory  434 . In one example, the processor  432  stores the pose in a look-up table in memory  434 . The processor  432  may set up the look-up table in memory and maintain the look-up table during a visual-inertial tracking process by eyewear device  100 . The look-up table may include an entry corresponding to each line of a rolling shutter camera (or, for example, an entry for each line having a different pose than a preceding line due to camera motion), with the first pose stored in the first line of the look-up table. 
     At step  844 , the eyewear device  100  captures, during a capture period, a second image of an environment using the camera system. The second image includes feature points with each feature point being captured at a particular capture time during the capture period. The processor  432  may continuously receive input images from the second visible light camera  114  and store those images in memory  434  for processing. In some examples, the eyewear device  100  may compare objects in the captured images to objects stored in a library of images to identify a match, e.g., for use in determining the position of the eyewear device through visual-inertial tracking (described below). A library of images of known objects is stored in a virtual object database  484  for comparison. 
     At block  846 , the eyewear device  100  senses movement of the mobile device at a plurality of times during the capture period by obtaining motion information from the physical environment  600  near the device  100  from various sensors, for example, location information from a GPS unit  473 , orientation information from an IMU  472  or distance information from a laser distance sensor. In an example, processor  432  retrieves sensed parameters from at least one of GPS  473 , IMU  472 , a laser distance sensor, cameras  114 , or a combination thereof. The processor then determines motion and position information from the sensed parameters using techniques described herein. 
     At block  848 , the eyewear device  100  computes a number of poses for the second rolling shutter camera based on the initial pose and the sensed movement, each computed pose corresponding to a particular computed time within the capture period. The number of computed poses for the second rolling shutter camera is responsive to the sensed movement of the mobile device. The number of poses to compute can be determined as described above with reference to block  808 . To calculate each of the number of poses, the processor  432 , for example, determines a head pose (roll, pitch, and yaw) of the eyewear device  100  within the environment by using motion and position information obtained from sensors (see block  806 ). In one example, the processor  432  of the eyewear device  100  determines its position with respect to one or more objects  604  within the environment  600  using captured images, constructs a map of the environment  600  using a coordinate system (x, y, z) for the environment  600 , and determines its position within the coordinate system. For example, the processor  432  may determine a head pose (roll, pitch, and yaw) of the eyewear device  100  within the environment by using two or more location points (e.g., three location points  606   a ,  606   b , and  606   c ) associated with a single object  604   a , or by using one or more location points  606  associated with two or more objects  604   a ,  604   b ,  604   c . In another example, the processor  432  determines the head pose using other sensors (e.g., IMU  472  or GPS  473 ) in addition to or instead of captured images. In one example, the processor  432  determines the pose for a line using a simultaneous localization and mapping (SLAM) algorithm applied to data received from one or more sensors for a first pose during exposure of a first line of the second rolling shutter camera. 
     At block  850 , the eyewear device  100  selects, for each feature point in the second image, one of the number of second camera computed poses by matching the particular capture time for the feature point to the particular computed time for the computed pose. 
     At block  852 , the eyewear device  100  determines a position of the mobile device within the environment using the feature points and the selected second camera computed poses for the feature points of the second image. 
     Any of the functionality described herein can be embodied in one more computer software applications or sets of programming instructions, as described herein. According to some examples, “function,” “functions,” “application,” “applications,” “instruction,” “instructions,” or “programming” are program(s) that execute functions defined in the programs. Various programming languages can be employed to implement one or more of the applications, structured in a variety of manners, such as object-oriented programming languages (e.g., Objective-C, Java, or C++) or procedural programming languages (e.g., C or assembly language). In a specific example, a third-party application (e.g., an application developed using the ANDROID™ or IOS™ software development kit (SDK) by an entity other than the vendor of the particular platform) may include mobile software running on a mobile operating system such as IOS™, ANDROID™, WINDOWS® Phone, or another mobile operating systems. In this example, the third-party application can invoke API calls provided by the operating system to facilitate functionality described herein. 
     Hence, a machine-readable medium may take many forms of tangible storage medium. Non-volatile storage media include, for example, optical or magnetic disks, such as any of the storage devices in any computer devices or the like, such as may be used to implement the client device, media gateway, transcoder, etc. shown in the drawings. Volatile storage media include dynamic memory, such as main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fiber optics, including the wires that comprise a bus within a computer system. Carrier-wave transmission media may take the form of electric or electromagnetic signals, or acoustic or light waves such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media therefore include for example: a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, punch cards paper tape, any other physical storage medium with patterns of holes, a RAM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave transporting data or instructions, cables or links transporting such a carrier wave, or any other medium from which a computer may read programming code or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. 
     Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims. 
     It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “includes,” “including,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises or includes a list of elements or steps does not include only those elements or steps but may include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     Unless otherwise stated, any and all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. Such amounts are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. For example, unless expressly stated otherwise, a parameter value or the like may vary by as much as ± 10 % from the stated amount. 
     In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various examples for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim. Rather, as the following claims reflect, the subject matter to be protected lies in less than all features of any single disclosed example. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter. 
     While the foregoing has described what are considered to be the best mode and other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present concepts.