Patent Publication Number: US-9851206-B2

Title: Marine navigation device with improved contour lines

Description:
RELATED APPLICATIONS 
     The present application is a continuation of, and claims priority benefit to, co-pending and commonly assigned U.S. non-provisional patent application entitled “MARINE NAVIGATION DEVICE WITH IMPROVED CONTOUR LINES,” application Ser. No. 14/449,688, filed Aug. 1, 2014, which claims the benefit under 35 U.S.C. §119(e) of provisional U.S. patent application Ser. No. 61/861,883, filed Aug. 2, 2013, titled “IMPROVED HYDROGRAPHIC TECHNIQUES,” and provisional U.S. patent application Ser. No. 61/904,909, filed Nov. 15, 2013, titled “IMPROVED HYDROGRAPHIC TECHNIQUES.” These earlier-filed applications are hereby incorporated by reference into the current application in their entirety. 
    
    
     BACKGROUND 
     Marine navigation devices often include a display that shows a map of at least a portion of a body of water in the vicinity of the current geolocation of a marine vessel with which the marine navigation device is being utilized. The map may include a representation of the terrain or soil at the bottom of the water with contour lines which indicate locations of the terrain that are at the same depth. Marine navigation devices display contour lines associated with depths of a plurality of geographic areas associated with a body of water. The displayed contour lines are presented in a higher density for areas associated with, large gradients or slopes of the underwater terrain, while flatter underwater regions result in a lower contour line density. Conventional marine navigation devices may remove an entire contour line to reduce the density of contour lines presented on a display. 
     SUMMARY 
     Embodiments of the present technology provide a marine navigation device that displays a map for a body of water which includes contour lines to indicate all of the geolocations of the terrain that exist at the same depth of water in the vicinity of a marine vessel. The marine navigation device may increase visibility of other information displayed about the body of water by selectively reducing a portion of the contour lines that are shown. The marine navigation device comprises a location determining element, a display, a memory element, and a processing element. The location determining element determines a current geolocation of a marine vessel on a first body of water. The display displays a map representation. The memory element stores digital elevation model data and sonar data for a plurality of bodies of water. 
     The processing element is in communication with the memory element and is configured to select the digital elevation model data or the sonar data from the memory element corresponding to the first body of water and calculate contour line data using the digital elevation model data or the sonar data for at least a portion of the first body of water, wherein the contour line data determines a plurality of contour lines, with each contour line indicating all of the geolocations of underwater terrain that exist at a depth of water. The processing element is further configured to update the contour line data by selectively removing at least a portion of the contour lines, generate a map representation of at least a portion of the first body of water corresponding to the current geolocation, wherein the map representation includes contour lines derived from the updated contour line data, and control the display to visually present the map representation. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present technology will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the present technology is described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a perspective view of a marine navigation device constructed in accordance with various embodiments of the current technology; 
         FIG. 2  is a schematic block diagram of various components of the marine navigation device; 
         FIG. 3A  is a screen capture from a display of the marine navigation device depicting a map of a body of water, the map including a plurality of contour lines, bottom hardness shading, and safety shading; 
         FIG. 3B  is a screen capture from the display wherein a plurality of hatching lines indicates the safety shading; 
         FIG. 4  is a three-dimensional image of the body of water; 
         FIG. 5  is a view of a portion of the map depicting a plurality of contour lines before contour line thinning has occurred; and 
         FIG. 6  is a view of the portion of the map from  FIG. 5  depicting the contour lines after contour line thinning has occurred. 
     
    
    
     The drawing figures do not limit the present technology to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the technology. 
     DETAILED DESCRIPTION 
     The following detailed description of the technology references the accompanying drawings that illustrate specific embodiments in which the technology can be practiced. The embodiments are intended to describe aspects of the technology in sufficient detail to enable those skilled in the art to practice the technology. Other embodiments can be utilized and changes can be made without departing from the scope of the present technology. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present technology is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     Embodiments of the present technology relate to a marine navigation device utilized with a marine vessel or water craft for navigating on a body of water. The marine navigation device may be any computing device. For instance, the marine navigation device may be a tablet, cellular phone, or handheld mobile device. The device typically includes a location determining element for determining a current geolocation of the marine vessel. The location determining element may also determine a route for the marine vessel to follow in navigating from the current geolocation to a destination. The device also includes a display which usually displays a map of the body of water in the vicinity of the marine vessel. When appropriate, the display may also show a map of the land adjacent to the body of water. In some instances, representations of the land may include satellite imagery. The display may further show a representation of the marine vessel overlayed on the body of water—typically at a position that indicates the current geolocation of the marine vessel. In some cases, the display may include touchscreen functionality wherein there are a plurality of icons shown on the display that allow a user to adjust the zoom level of the map, change other settings, or look at menus. 
     The display may further show contour lines on the body of water portion of the map that indicate all of the geolocations of the underwater terrain that exist at the same depth of water. The contour lines may also indicate underwater channels or other features that can help the user navigate the water. The contour lines may be shown at various depth ranges, such as every foot, every two feet, every five feet, and so forth. A density of the contour lines may be defined as the number of lines per unit length or unit area of the display screen. Often, the density increases in areas of the display which correspond to areas of the underwater terrain where there are significant slopes or gradients. For example, if contour lines are presented in increments of 5 feet (e.g., a separate contour line is presented for depths of 25, 30, 35, and 40 feet), a rapid change of depth of 20 feet may result in four contour lines being presented in close proximity to one another. The increased concentration of contour lines for a geographic area may partially obstruct the underlying map content associated with the geographic area. When the density of contour lines becomes too great, then the crowding of contour lines in those areas dominate the map and obstruct the underlying map content. Conventional devices may remove one or more contour lines presented on a display in order to reduce the density of contour lines. Some conventional devices may enable the user to remove contour lines to examine the map content obstructed by contour lines concentrated in an area of the map. The conventional devices do not identify portions of adjacent contour lines such that the portion of each contour line that is obstructing map information provided to a user may be identified and selectively removed. 
     Embodiments of the technology will now be described in more detail with reference to the drawing figures. Referring initially to  FIGS. 1-3B , a marine navigation device  10  is illustrated which is configured to display a map  12  of a body of water that includes contour lines to indicate all of the geolocations of the terrain that exist at the same depth of water in the vicinity of a marine vessel. The marine navigation device  10  may increase visibility of other information displayed about the body of water by selectively reducing a portion of the contour lines that are shown. The marine navigation device  10  broadly comprises a housing  14 , a display  16 , a user interface  18 , a communication element  20 , a location determining element  22 , a memory element  24 , and a processing element  26 . 
     The housing  14 , as shown in  FIG. 1 , generally encloses and protects the other components from moisture, vibration, and impact. The housing  14  may include mounting hardware for removably securing the marine navigation device  10  to a surface within the marine vessel or may be configured to be panel-mounted within the marine vessel. The housing  14  may be constructed from a suitable lightweight and impact-resistant material such as, for example, plastic, nylon, aluminums, or any combination thereof. The housing  14  may include one or more appropriate gaskets or seals to make it substantially waterproof or resistant. The housing  14  may take any suitable shape or size, and the particular size, weight and configuration of the housing  14  may be changed without departing from the scope of the present technology. 
     The display  16 , as shown in  FIG. 1 , may include video devices of the following types: plasma, light-emitting diode (LED), organic LED (OLED), Light Emitting Polymer (LEP) or Polymer LED (PLED), liquid crystal display (LCD), thin film transistor (TFT) LCD, LED side-lit or back-lit LCD, heads-up displays (HUDs), or the like, or combinations thereof. The display  16  may possess a square or a rectangular aspect ratio and may be viewed in either a landscape or a portrait mode. In various embodiments, the display  16  may also include a touch screen occupying the entire screen or a portion thereof so that the display  16  functions as part of the user interface  18 . The touch screen may allow the user to interact with the marine navigation device  10  by physically touching, swiping, or gesturing on areas of the screen. The display  16  may be capable of displaying the map  12  of the body of water along with a representation of the marine vessel overlayed thereon. 
     The user interface  18  generally allows the user to utilize inputs and outputs to interact with the marine navigation device  10 . Inputs may include buttons, pushbuttons, knobs, jog dials, shuttle dials, directional pads, multidirectional buttons, switches, keypads, keyboards, mice, joysticks, microphones, or the like, or combinations thereof. Outputs may include audio speakers, lights, dials, meters, or the like, or combinations thereof. With the user interface  18 , the user may be able to control the features and operation of the display  16 . For example, the user may be able to zoom in and out on the display  16  using either virtual onscreen buttons or actual pushbuttons. In addition, the user may be able to pan the image on the display  16  either by touching and swiping the screen of the display  16  or by using multidirectional buttons or dials. 
     The communication element  20  generally allows communication with external systems or devices. The communication element  20  may include signal or data transmitting and receiving circuits, such as antennas, amplifiers, filters, mixers, oscillators, digital signal processors (DSPs), and the like. The communication element  20  may establish communication wireless by utilizing radio frequency (RF) signals and/or data that comply with communication standards such as cellular 2G, 3G, or 4G, Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard such as WiFi, IEEE 802.16 standard such as WiMAX, Bluetooth™, or combinations thereof. In addition, the communication element  20  may utilize communication standards such as ANT, ANT+, Bluetooth™ low energy (BLE), the industrial, scientific, and medical (ISM) band at 2.4 gigahertz (GHz), or the like. Alternatively, or in addition, the communication element  20  may establish communication through connectors or couplers that receive metal conductor wires or cables or optical fiber cables. The communication element  20  may be in communication with the processing element  26  and the memory element  24 . 
     The location determining element  22  generally determines a current geolocation of the marine navigation device  10  and may receive and process radio frequency (RF) signals from a global navigation satellite system (GNSS) such as the global positioning system (GPS) primarily used in the United States, the GLONASS system primarily used in the Soviet Union, or the Galileo system primarily used in Europe. The location determining element  22  may accompany or include an antenna to assist in receiving the satellite signals. The antenna may be a patch antenna, a linear antenna, or any other type of antenna that can be used with location or navigation devices. The location determining element  22  may include satellite navigation receivers, processors, controllers, other computing devices, or combinations thereof, and memory. The location determining element  22  may process a signal, referred to herein as a “location signal”, from one or more satellites that includes data from which geographic information such as the current geolocation is derived. The current geolocation may include coordinates, such as the latitude and longitude, of the current location of the marine navigation device  10 . The location determining element  22  may communicate the current geolocation to the processing element  26 . 
     Although embodiments of the location determining element  22  may include a satellite navigation receiver, it will be appreciated that other location-determining technology may be used. For example, cellular towers or any customized transmitting radio frequency towers can be used instead of satellites may be used to determine the location of the marine navigation device  10  by receiving data from at least three transmitting locations and then performing basic triangulation calculations to determine the relative position of the device with respect to the transmitting locations. With such a configuration, any standard geometric triangulation algorithm can be used to determine the location of the marine navigation device  10 . The location determining element  22  may also include or be coupled with a pedometer, accelerometer, compass, or other dead-reckoning components which allow it to determine the location of the device  10 . The location determining element  22  may determine the current geographic location through a communications network, such as by using Assisted GPS (A-GPS), or from another electronic device. The location determining element  22  may even receive location data directly from a user. 
     The memory element  24  may include data storage components such as read-only memory (ROM), programmable ROM, erasable programmable ROM, random-access memory (RAM) such as static RAM (SRAM) or dynamic RAM (DRAM), hard disks, floppy disks, optical disks, flash memory, thumb drives, universal serial bus (USB) drives, or the like, or combinations thereof. The memory element  24  may include, or may constitute, a “computer-readable medium”. The memory element  24  may store the instructions, code, code segments, software, firmware, programs, applications, apps, services, daemons, or the like that are executed by the processing element  26 . The memory element  24  may also store settings, data, documents, sound files, photographs, movies, images, databases, and the like. 
     In various embodiments, the memory element  24  may further store sonar data, digital elevation model (DEM) data, and the like. The sonar data may be presented in the form of a database and may include the coordinates for a plurality of geolocations and at least one depth of water associated with each geolocation. In various embodiments, the sonar data may be gathered by a separate marine vessel using a sound navigation and ranging (sonar) element. Typically, the sonar element generates a sound beam or wave at one or more frequencies into the water and measures the amount of time that elapses before the reflection of the sound beam from the bottom surface of the body of water or an object is received. In embodiments, the depth of the water or the distance to underwater objects in the path of the beam can be determined from the time delay or other characteristic of the received sonar beam. In addition, the backscatter intensity, the amplitude, the energy level, or a similar characteristic of the returned sound beam may indicate the density of objects in the path of the beam. In the case of the underwater terrain, a hardness value of the soil of the water bottom may be determined from the returned sound beam. The entire body of water may be swept in order to gather the sonar data, such that the sonar data includes substantially all of the geolocations of the body of water, wherein “substantially all” refers to all of the water-covered areas that are navigable by a marine vessel or water craft. The sonar data for the body of water may be stored in the memory element  24  before the marine navigation device  10  is utilized for an outing on the body of water. 
     The DEM data generally includes location information, such as coordinates for a plurality of geolocations. In embodiments, the location information may be positioned at the intersection points of a geographical grid associated with a particular region of a body of water. Associated with each geolocation is a value for an elevation or height, which is usually the elevation above sea level, of the terrain. The marine navigation device may determine that a geographic location is associated with a body of water based on a depth level determined for the body of water. The DEM data usually covers substantially all of a body of water and typically includes substantially the same geolocations as are included in the sonar data. In addition, the DEM data is typically stored in the memory element  24  before the marine navigation device  10  is utilized for an outing on the body of water. 
     The memory element  24  may further store data for the map  12  that represents the geographic area covered by the body of water as well as the geographic area surrounding the body of water. The memory element  24  may also store contour line data for a plurality of contour lines  34  that are overlayed on the map  12 , as shown in  FIGS. 3A and 3B . The contour line  34  data may be generated by an external source and stored in the memory element  24 . Each contour line  34  may connect all of the geolocations of the terrain that exist at the same depth of water. For example, the memory element  24  may store contour line data for all of the geolocations that are at a depth of 1 foot, 2 feet, 3 feet, and so forth. Alternatively, the memory element  24  may store contour line data for all of the geolocations that are at other ranges of depths, such as every 2 feet, every 5 feet, and so forth. The user may be able to choose the ranges of depths for which a contour line  34  is indicated and shown on the display  16 . Generally, there may be multiple contour lines  34  displayed for a body of water for the same depth, as one region may have a first contour line  34  at a first depth while another geographically separated region may have a second contour line  34  at the first depth as well. For example, a underwater terrain for a body of water may have a plurality of elevated and lower portions separated by areas having different depths. Furthermore, each contour line  34  may include a plurality of line segments that are connected to one another to form the contour line  34 . 
     The contour line  34  data stored in the memory element  24  may be configured such that the contour lines  34  have a reduced density, wherein the density may be related to the number of lines per unit area or the spacing between adjacent lines. In order to reduce the density of the contour lines  34 , some segments or portions of certain contour lines  34  may not be included in the data if they will appear too close to segments of other contour lines  34  when the map  12  and the overlayed contour lines  34  are shown on the display  16 . The specific segments of contour lines  34  to be excluded from the data may be determined based expected characteristics, parameters, or features of the display  16 . This reduces clutter created on the display  16  caused by an overabundance of contour lines  34  for a portion of a map  12  displayed with contour lines  34 . In addition, the processing element  26  may actively reduce the density of the contour lines  34 , as discussed below. 
     The memory element  24  may also store bottom hardness shading data which can be used to render an image of the soil at the bottom of the body of water with shading  28  that indicates the hardness of the soil, such as the images shown in  FIGS. 3A and 3B . The bottom hardness shading data may be generated by an external source and may include a value of a monochromatic shade of a first color for each geolocation occupied by the body of water. In exemplary embodiments, the first color may be white or black such that the monochromatic shade value is a grayscale value. In other embodiments, the first color may be another color, such as brown, and the monochromatic shades may be varying shades of brown. The monochromatic shade value may be based on a hardness value of the soil for the given geolocation and may range from 0 to 255, as an example. The soil hardness values may be retrieved or collected from diving expeditions or the use of a dredging tool. In addition, the soil hardness data may be inferred from historical substrate maps. In an exemplary embodiment, the monochromatic shade values are based on the soil hardness values such that lighter shades of the first color represent soils that are harder or denser, while darker shades represent softer or less dense soils. In addition, the processing element  26  may generate the bottom hardness shading data, as discussed below. 
     The processing element  26  may include processors, microprocessors, microcontrollers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), analog and/or digital application-specific integrated circuits (ASICs), or the like, or combinations thereof. The processing element  26  may generally execute, process, or run instructions, code, code segments, software, firmware, programs, applications, apps, processes, services, daemons, or the like, or may step through states of a finite-state machine, or combinations of these actions. The processing element  26  may be in communication with the other electronic components through serial or parallel links that include address busses, data busses, control lines, and the like. 
     The processing element  26  may be configured to determine the features of the content that is shown on the display  16 . For example, the processing element  26  may determine the location and size of the user interface  18  portion of the display  16  as well as the location and size of the map  12 . The processing element  26  may also be configured to determine the content of the map  12 , based on factors such as the current geolocation of the marine vessel as well as settings chosen by the user such as the zoom level, among other factors. 
     In some embodiments, as an alternative to having pre-determined bottom hardness shading data stored in the memory element  24 , the processing element  26  may be configured to calculate, compute, or determine the bottom hardness shading data in order to implement the bottom hardness shading  28 . The bottom hardness shading data generated by the processing element  26  may be substantially similar to the bottom hardness shading data that is stored in the memory element  24 . The processing element  26  may assign the monochromatic shade value of the first color for each geolocation based on the hardness value of the soil in that location. The soil hardness values may be derived from the sonar data. As with the bottom hardness data stored in the memory element  24 , the processing element  26  may generate monochromatic shade values such that lighter shades of the first color represent soils that are harder or denser, while darker shades represent softer or less dense soils. The monochromatic shades indicated by the bottom hardness shading data may be overlayed on the map  12 , as shown in  FIGS. 3A and 3B . 
     The processing element  26  may also be configured to calculate, compute, or determine depth shading data. From the memory element  24 , the processing element  26  may receive the sonar data, the DEM data, or both. While the DEM data may provide only elevation data, water depth data can be derived from the DEM data. The depth shading data may include a shade of a color value for at least a portion of the geolocations of the body of water—typically for those geolocations whose depth of water meets a certain criteria. For example, the processing element  26  may implement a safety shading  30  to highlight shallow water areas of the body of water. Thus, the depth shading data may include an incrementally varying shade value of a second color for those areas of the body of water that have a depth of a first depth threshold or less. For example, the first depth threshold may be 20 feet. Accordingly, the processing element  26  may determine a shade value of the second color for those geolocations which are to be displayed on the map  12  whose depth is included in the range from 0 feet to 20 feet. The color shade value may vary according to an interval, such as every foot, every 2 feet, or so forth. In exemplary embodiments, the color shades may be increasingly darker as the depth of water decreases, such that the darkest color shade is assigned to the shallowest water. In addition, exemplary colors may include purple or blue. The safety shading  30  indicated by the depth shading data may be overlayed on the map  12 , as seen in  FIG. 3A .  FIG. 3B  also shows safety shading  30 , wherein the safety shading  30  is indicated by horizontal hatching lines to more clearly highlight the safety shading  30  in the shallow water areas. 
     In certain embodiments, the processing element  26  may generate depth shading data to further include a value of a single color for those geolocations with a depth between a given range or a depth greater than a given value. In exemplary embodiments, the processing element  26  may generate depth shading data to include a value for the color magenta, or a similar color, for those geolocations with a depth at a certain range. The color may be overlayed on the map  12 . Thus, those geolocations with a depth, for example, greater than 50 feet may appear on the map  12  shaded in magenta. 
     The processing element  26  may further be configured to calculate, compute, or determine three-dimensional terrain data from the sonar data, the DEM data, or both. The three-dimensional terrain data may be utilized to create a three-dimensional image  32  of the body of water as seen from an overhead perspective that is behind the marine vessel. As appropriate according to zoom level settings and proximity to land of the marine vessel, the three-dimensional image  32  may further include a three-dimensional perspective representation of the land at the shoreline of the body of water. In addition, the three-dimensional terrain data may include relief shading to indicate shadows of the underwater terrain as created by a natural or artificial light source. The processing element  26  may communicate the three-dimensional image  32  derived from the three-dimensional terrain data to the display  16 , as shown in  FIG. 4 , instead of communicating the map  12  to the display  16 . The representation of the marine vessel may be overlayed on the three-dimensional image  32  at a position corresponding to the current geolocation of the marine vessel. 
     The processing element  26  may also be configured to determine a route along the body of water from the current geolocation of the marine vessel to a user-specified geolocation. The processing element  26  may determine the route based on the sonar data, the DEM data, or both. For example, the route may be plotted through areas of the body of water that are deep enough for the marine vessel to safely navigate or areas that have relatively hard soil. In addition, when shown on the display  16 , the route may be overlayed on the map  12  or on the three-dimensional image  32  of the body of water. 
     In some embodiments, as an alternative to having pre-determined contour line  34  data stored in the memory element  24 , the processing element  26  may additionally be configured to determine contour line data for the contour lines  34  similar to the contour line  34  data stored in the memory element  24 . The sonar data, the DEM data, or both may be utilized in determining the contour line data. 
     The density of the contour lines  34 , when they are shown on the display  16 , may depend on a number of factors, such as a zoom level of the map  12  on the display  16 , the depth range of the contour lines  34 , and the topography of the underwater terrain, among other factors. In some embodiments, the contour line density is similar for varying zoom levels of the map  12 . In other embodiments, the contour line density is inversely proportional to the zoom level of the map  12 , wherein a larger zoom level (zooming in) generally results in a lower contour line density and greater space between adjacent contour lines  34 , while a smaller zoom level (zooming out) results in a greater contour line density and less space between adjacent contour lines  34 . In addition, the contour line density may be inversely proportional to the depth range, wherein a larger depth range (e.g., 10 feet) results in a lower contour line density, while a smaller depth range (e.g., 1 foot) results in a greater contour line density. 
     The user may, to a certain extent, control the contour line density by adjusting the zoom level of the map  12  on the display  16 , adjusting the contour line depth range, or both. However, in some situations, the contour line density may be high in certain areas of the map  12  even after the zoom level and the depth range have been adjusted. Typically, these onscreen areas correspond to areas of the underwater terrain where there are large gradients. The user may choose to not change the appearance of the contour lines  34  on the map  12 , or he may have the option of reducing the density of contour lines  34  as described below. 
     In embodiments, the processing element  26  may determine a line to line distance as a distance between adjacent contour lines  34  before they are shown on the map  12 , based on the current settings for the display  16  zoom level or the contour line depth range. A contour line threshold value for the line to line distance may be used to reduce the density of contour lines  34  displayed on the map  12 . The contour line threshold value may be a distance between geographic locations associated with the underwater terrain (e.g., 10 feet between geographic coordinates associated with adjacent contour lines  34 ) or a display distance between contour lines  34 , which may vary based on the size of display  16  (e.g., one-sixteenths of an inch between points of adjacent contour lines  34  presented on an 8-inch display  16 ). The contour line threshold value may be established either at the time of production for the marine navigation device  10  or by the user during usage of the device  10 . For portions of the contour lines  34  having a line to line distance is less than the contour line threshold value, the processing element  26  may reduce the contour line density by removing one or more segments from one or more contour lines  34 . The processing element  26  may update the contour line data before the contour lines  34  are presented on the map  12 . If the line to line distance is greater than or equal to the contour line threshold, then the contour lines  34  may be shown on the map  12  without modification. 
     In an exemplary embodiment, the processing element  26  may perform the following actions to reduce the contour line density, or thin the presented contour lines  34 , before the contour lines  34  are shown on the map  12 . The processing element  26  may determine an area of the body of water having a group of three or more contour lines  34  such that the line to line distance of each adjacent pair of contour lines  34  is less than the contour line threshold value, as shown in  FIG. 5 , wherein there are two such groups. The processing element  26  may determine a window  36  that surrounds the area, such as the two windows shown in  FIG. 5 . (Although two windows  36  are shown in  FIG. 5 , the windows  36  are not actually drawn on the map  12  shown on the display  16 . The windows  36  are shown in the figures to illustrate part of an exemplary process of reducing the contour lines  34  presented on display  16 .) The processing element  26  may utilize the windows  36  to group adjacent contour lines  34  that may be reduced in density to improve the user experience when viewing the map  12  on display  16 . The processing element  26  may determine the two outermost contour lines  34  in the window  36  and identify those outermost contour lines  34  for continued presentation. For the contour lines  34  in between the two outermost contour lines  34 , the processing element  26  may remove the segments of those contour lines  34  that lie within the window  36 , as shown in  FIG. 6 . This reduces the density of contour lines  34  presented for a portion of a body of water and thereby reduces the obstruction of map  12  by contour lines  34 . Typically, each contour line  34  includes at least a segment or a portion that is extends beyond the perimeter of the window  36 . In embodiments, a contour line  34  having a portion thereof removed in a first window  36  may have the remaining portions of the contour line  34  presented on display  16 , which may include an adjacent second window  36 . In some cases, the processing element  26  may remove an entire contour line  34 , if the contour line  34  begins and ends within the window  36 . Once the contour line data has been updated, then the processing element  26  may communicate the contour line data to the display  16  to be shown as contour lines  34  on the body of water portion of the map  12 , as shown in  FIGS. 3A and 3B . As shown in  FIG. 6 , the reduced contour lines  34  enables a user to view more map information presented on display  16 , when compared to the original contour lines  34  shown in  FIG. 5 . In embodiments, the number and location of windows  36  may be automatically determined based on the current zoom level. For example, a group of contour lines  34  that may not be presented close to one another when display  16  presents map  12  and other information for a geographic area using an increased zoom level may be presented close to one another when the zoom level is decreased (a larger portion of map  16  is presented as a result). This dynamic grouping of contour lines  34  based on a current zoom level of display  16  by processing element  26  enables the outermost contour lines  34  to be presented on display  16  in an intuitive and user friendly manner. 
     While the marine vessel moves around the body of water, the area of the body of water that is shown in the map  12  changes. Accordingly, the processing element  26  may repeatedly evaluate the line to line distance of the contour lines  34  that are shown in the map  12 . As necessary, the processing element  26  may update the contour line data to reduce the contour line density by removing one or more segments from one or more contour lines  34 . In addition, the processing element  26  may update the contour line data when the user changes the zoom level or the contour line depth range. 
     The marine navigation device  10  may operate as follows. The device  10  may be utilized with a marine vessel that is engaging in boating activities on a body of water. The device  10  may assist a user in determining his current geolocation, generally navigating around the water, or the like. The display  16  of the device  10  may show the map  12  and the marine vessel overlayed on the map  12  at the current geolocation, as shown in  FIGS. 3A and 3B . 
     If so desired, the user may select any combination of a plurality of options for viewing information regarding the body of water. Through the user interface  18 , the user may apply bottom hardness shading  28  and safety shading  30  to the map  12 . In response, the processing element  26  may generate or adjust the bottom hardness shading data, the depth shading data, or both, as appropriate. Alternatively, the processing element  26  may retrieve and utilize the previously-stored bottom hardness shading data that is overlayed on the map  12 . In addition, the user may select the three-dimensional image  32  to be shown on the display  16 , as seen in  FIG. 4 , and the processing element  26  may generate or adjust the three-dimensional terrain data. Furthermore, the user may choose to plot a course from his current geolocation to a specific destination, and the processing element  26  may determine a route which is overlayed on the map  12  or the three-dimensional image  32 . The user may also choose to thin the contour lines  34  as they appear on the map  12 . In those areas where the line to line distance of the contour lines  34  is below the contour line threshold value (indicating high contour line density), the processing element  26  may update the contour line data to reduce the contour line density. Alternatively, the processing element  26  may retrieve and utilize the previously-stored contour line  34  data that has an already reduced line density, which eliminates the need for the processing element  26  to perform any calculations on the contour line  34  data. The user may zoom in or out on the map  12  or the three-dimensional image  32  using the user interface  18 . The user may also pan around on the map  12  or the three-dimensional image  32  in order to see areas of the body of water away from the current geolocation of the marine vessel. 
     The marine navigation device  10  may show useful information regarding the body of water on the map  12  in the form of shading and contour lines  34 . The bottom hardness shading  28  and safety shading  30  as well as the contour lines  34  may help the user safely navigate the marine vessel along the body of water. They may also help the user find good fishing and swimming areas. The processing element  26  may declutter the contour lines  34  that are shown on the map  12  by maintaining the line to line distance between adjacent contour lines  34  at or above the contour line threshold value. Since the display  16  may show shading information in the same area of the map  12  as the contour lines  34 , selectively removing contour line  34  segments in high-density areas may allow the user to more easily see the shading. 
     Although the technology has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the technology as recited in the claims.