MODELLING OF OBJECTS

Abstract: A model of a building can be created by comparing geometric features extracted from one or more images of the building with geographical information concerning the layout and position of the building. Features present on the building can be placed on the model by comparing and matching standard representations of building features (e.g. windows, doors, mouldings) with features shown in the images. The features to be included in the model can alternatively, or additionally, be determined by user input.

Description: MODELLING OF OBJECTS This application relates to the modelling of objects, particularly buildings in an environment. A known system for producing a computer model of a building is described in US patent number 5819016 (Watanabe et al). Watanabe et al describes a system for modelling an environment as seen from the view point of a roving observation device. The environment modelled is typically the interior of a building and objects, such as chairs, in the interior space are recognised by matching them to standard shapes represented by mathematical functions. This system is not suitable for creating a scaled model of an environment populated with buildings wherein the features present on the exterior surfaces of the buildings are also scaled appropriately. It is an object of the present invention to provide an improved system for modelling an environment populated with buildings in which the buildings, and features present on the buildings, are modelled to scale. The invention consists in a method of creating a model of a building comprising the steps of providing geometrical data of selected features of the building, providing geographical data of the building and correlating this with said geometrical data to determine the size and location of selected features in a model of the building, and providing reference data of standard building features and correlating this with the geometrical data so as to identify such standard features and to scale and position these standard features on a model of the building. Preferably, the geometrical data is derived by analysing image data. A system according to this embodiment could comprise, for example, means for analysing a digital image of a building to determine salient features of the building's geometry. Alternatively, the geometrical data is data input by a user which describes or specifies at least a part of the building. For example, a user could input a textual description of the building or a set of mathematical co-ordinates defining the building's geometry. In a preferred embodiment, the geometrical data is in part derived by analysing image data and in part provided by data input by a user which describes or specifies at least a part of the building. For example, image analysis could be supplemented by user input to provide a more detailed model, or the system could be arranged to refer back to a user for data input when there is no standard feature in the system which matches geometrical data determined to be a possible feature present in a building being modelled. The invention also consists in apparatus for performing the aforesaid method. One advantage of the present system is that economies can be achieved in the amount of data used in a model. Although the library of standard features used in the system may contain large amounts of data, this is offset when larger areas, such as cities, are modelled because of the accumulative savings in the amount of data required to model individual buildings, and the total data required including the library is much less than that for a digitised display of the city. It should also be noted that the data size of the system can be reduced by reducing the scope of the library of standard features, although it will be realised that this will produce a concomitant reduction in the detail of the model. Some embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a system for creating a model of a building; Figure 2 is a block diagram of a further system of creating a model of a building; and Figure 3 is a block diagram of another system for creating a model of a building. In a first embodiment shown in Figure 1 , image data 1 of a building is analysed by an image analyser 3 to produce geometrical data 5 relating to the building represented by the image data 1. The image data 1 can comprise photographic or video images of a building which the image analyser 3 processes using established machine vision and object edge recognition methods to produce certain geometrical data 5 relating to the building. The geometrical data 5 comprises data 7 describing the outline of the building and data 9 describing features of the building such as doors and windows. The geometrical data 5 can be, in effect, a "wire frame" representation of the building and its features as determined from the image data. An outline correlator 11 processes the outline data 7 of the geometrical data 5 and geographical data 13 in order to determine the initial raw building outline. Generally, the geographical data 13 describes the layout or plan of the building and comprises ground elevation map co-ordinates derived from, for example, national survey data. Using this data, the outline correlator 11 can achieve fairly accurate extrapolation and positioning of all external walls and surfaces of the building. Thus, a scaled outline description 15 is provided for the model 17. The scaled outline description 15 comprises data items for each surface of the building describing the position, size, orientation and texture of that surface. In one embodiment (not shown), images of a building to be modelled are captured using a camera which can sense its own position and orientation (e.g. via the Global Positioning System and an on-board inclinometer, respectively). This information about the location and viewing direction of the camera is then used in conjunction with the geographical data which comprises ordinance-survey 2D plans of the buildings in the environment to enable the outline correlator 11 to determine to which of the buildings in the environment the images relate. As will be appreciated, this adds a further degree of automation to the system in that the appropriate plan outline to be correlated with the images is selected automatically. Returning to Figure 1, feature correlator 19 takes the building features data 9 of the geometrical data 5 and correlates this with features from a library of standard building features 21. The standard features library 21 comprises a library of predefined, generic, scaleable building components, geometries and graphical entities. The standard features library 21 is arranged as a hierarchical "thesaurus" and is a systematical "store house" of archetypal building objects such as wall-types, door-types, window-types, roof-types, chimney-types, etc. The feature correlator 19 determines the presence, size and position of standard building features on the building by comparing the standard features from library 21 with the building features data 9 of the geometrical data of the building 5. Thus, scaled present standard features 23 are provided to the model 17 of the building. If the feature correlator 19 cannot find a match for a building feature 9 then it can, if required, choose a nearest match from the standard features library 21. However, it is preferable that complete anomalies are ignored all together since this helps to surpress unwanted "noise" in geometrical data which arises from the image data, e.g. trees, bicycles, pigeons etc. The outline correlator 11 and the feature correlator 19 each utilise appropriate rules for identifying the outline and features of the building to be modelled and are capable of extrapolation of partially concealed or partially missing features, walls or edges. If required, the model can be related back to the original photographic or video images in a further correlation step (not shown) by using standard digital photogrammetric techniques by selecting suitable control points from the outline model to compare with the images. In this way an indication of the accuracy of the model 17 can be obtained. Additionally, the model can take into account surface properties of the building to be modelled such as texture and colour. The system described above can be used to model an entire built-up environment. Such a model finds wide application including geographical information systems, virtual reality and personal navigation systems. Figure 2 shows a modification of the system described above with reference to Figure 1. If the feature correlator 19 cannot find a match for what seems to be, according to the feature correlator's rules, a building feature 9 in the geometrical data 5 in the standard features library 21 using its rule set, then it passes the unidentified feature 25 to an operator for identification 27. These operator identified features are then forwarded to the scaled present standard features 23 of the model 17 of the building. For instance, if the system is able to determine that a window is present but is unable to determine the type or style of the window then the matter is be referred to a user for determination. A further variant of the system of Figure 1 is shown in Figure 3. In this embodiment, operator input is used to assist the correlators 11 and 19. For example, the system can use textual information about features 29 as a clue or prompt during the feature matching process performed by feature correlator 19. For example, the operator input feature characteristics 29 used to assist the feature correlator 19 can comprise the building's date of origin or date of extension which would help greatly in the standard feature matching process. In a further embodiment, the geometrical data 5 could be input to the system directly in order to avoid the use of image analysis. A user could select standard features which are present on a building and their size through an appropriate user interface. Menu driven user interfaces are particularly appropriate for this task since they are well suited to hierarchical structures such as the standard features library. The models produced by the systems described above are information rich, interactive and may be queried in the same manner as a database. For example, the model could be queried to determine the number of north facing Victorian bay windows in Brighton. This model can also be corrected easily by changing characteristics found in the model. For example, altering the model by changing the description of a window from Georgian to Victorian would have the desired follow-through effect on the model as presented on a display.

Claims: Claims 1. A method of creating a model of a building comprising the steps of providing geometrical data of selected features of the building, providing geographical data of the building and correlating this with said geometrical data to determine the size and location of selected features in a model of the building, and providing reference data of standard building features and correlating this with the geometrical data so as to identify such standard features and to scale and position these standard features on a model of the building. 2. A method according to claim 1, wherein the step of providing geometrical data comprises deriving at least part of the geometrical data from image data. 3. A method according to claim 2, wherein the image data is provided by a digital camera provided with means for determining its position and orientation. 4. A method according to claim 3, wherein information about the position and orientation of the digital camera is used in the correlation of the geometrical and geographical data. 5. A method according to any preceding claim, wherein the step of providing geometrical data comprises deriving at least part of the geometrical data from user input, such as textual input. 6. A method according to any preceding claim, wherein at least part of the geometrical data is provided by user input, such as textual input. 7. A method according to any preceding claim, wherein the geographical data comprises information about the position and/or layout of the building(s) being modelled. 8. A method according to any preceding claim, wherein the step of correlating geometrical and reference data comprises seeking user instructions when the correlation is deemed to be unsuccessful. . A method according to any preceding claim, further comprising correlating the model of a building with the geometrical or image data relating to the building. 10. A method according to any preceding claim, wherein the reference data comprises a library of standard building features. 11. Apparatus for creating a model of a building, comprising geographical data correlating means for correlating geographical data with geometrical data of selected features of a building to be modelled to determine the size and location of selected features of the building, reference data correlating means for correlating reference data of standard building features with the geometrical data, and means for scaling and positioning standard building features on a model of the building. 12. Apparatus according to claim 11, comprising means for deriving at least part of the geometric data from image data. 13. Apparatus according to claim 12, wherein the image data is provided by a digital camera provided with means for determining its position and orientation. 14. Apparatus according to claim 13, wherein the geographical data correlating means is arranged to use information about the position and orientation of the digital camera in the correlation of the geometrical and geographical data. 15. Apparatus according to any one of claims 11 to 14, comprising means for deriving at least part of the geometric data from user input, such as textual input. 16. Apparatus according to any one of claims 11 to 15, comprising means for accepting at least part of the geometrical data as user input, such as textual input. 17. Apparatus according to any one of claims 11 to 16, wherein the geographical data comprises information about the position and/or layout of the building(s) being modelled. 18. Apparatus according to any one of claims 11 to 17, wherein the reference data correlating means is arranged to seek user instructions when the correlation is deemed to be unsuccessful. 19. Apparatus according to any one of claims 11 to 18, further comprising accuracy determining means for correlating the model of a building with the geometrical or image data relating to the building. 20. Apparatus according to any one of claims 11 to 19, wherein the reference data comprises a library of standard building features.

Inventors: BIDE STEPHEN, BIDE, STEPHEN
Applicants: BIDE STEPHEN, BIDE, STEPHEN
Application year: 2000
Main classification: G06T17
IPC codes: G06T17