Method and apparatus for producing digital orthophotos using sparse stereo configurations and external models

Abstract

A method and system for producing digital orthophotos from imagery acquired as full or sparse stereo. The orthophotos can be produced in a variety of map coordinate systems without the need to convert or recompute DEM or photogrammetric solution data. In one embodiment, a two-dimensional, planimetric free-network solution, utilizing arbitrary datum definition constraints, is used to provide a transitory coordinate system that is used to facilitate the image measurement process. It is utilized as a preliminary step to refine apriori block layout information to facilitate point picking and to provide general quality control capabilities before undertaking a rigorous 3D photogrammetric adjustment. In place of a general map conversion transformation, an identity transformation can be used, so that map coordinates and world coordinates are identical. With this process, given DEM data and photogrammetric solution data in a particular coordinate system, the orthophoto image data can be produced in any map coordinate system. In one embodiment, all geometric coordinate transformations are performed prior to performing the image intensity interpolation operation. Thus, only one image intensity interpolation operation is performed, using the geometric coordinate data. In another embodiment, a network constraint is introduced to the block adjustment process that assumes an average vertical direction in order to support the process of self rectification.

1 . A method for providing elevation model data for use in producing a digital orthophoto of a project area; said method comprising the steps of: 
 acquiring elevation model data from at least first and second sources;    prioritizing the elevation model data acquired from the first and second sources;    storing the elevation model data for at least the first and second elevation models in a memory in a predetermined order to produce an elevation multimodel;    accessing the elevation model data having the highest priority to provide elevation data for use in performing a first geometric transformation; and    accessing the elevation model data having the next priority to provide elevation data for use in performing a second geometric transformation.    
   
   
       2 . The method according to  claim 1 , wherein the elevation model data for the first and second elevation models are stored in contiguous data storage locations within the memory.  
   
   
       3 . The method according to  claim 1 , wherein the elevation multimodel is used as a source of external control to constrain a photogrammetric adjustment.  
   
   
       4 . The method according to  claim 1 , wherein the elevation multimodel is used as a source of external control in an orthorectification process.  
   
   
       5 . The method according to  claim 1 , wherein the elevation multimodel is used as a source of one-dimension elevation model data in deriving full three-dimensional data from a two dimension map and a one-dimension elevation model.  
   
   
       6  The method according to  claim 1 , wherein the elevation multimodel is used as a source of external control to constrain a photogrammetric adjustment process.  
   
   
       7 . A method for producing a digital orthophoto from a block of overlapping images of a project area; said method comprising the steps of: 
 acquiring imagery data for the project area;    performing a plurality of geometric coordinate transformations on the imagery data to obtain geometric coordinate data; and    performing only one image intensity interpolation operation using the geometric coordinate data, wherein all of said geometric coordinate transformations are performed prior to performing said image intensity interpolation operation.    
   
   
       8 . The method according to  claim 7 , wherein the step of performing a plurality of geometric coordinate transformations includes performing at least one photogrammetric orientation and performing at least one cartographic transformation.  
   
   
       9 . A method for producing a digital orthophoto from a block of overlapping images of a project area; said method comprising the steps of: 
 obtaining imagery data expressed in cartographic coordinates;    transforming the cartographic coordinates to world coordinates to obtain imagery data expressed in world coordinate data;    using the world coordinate data to obtain elevation value data from an elevation model expressed in world coordinates;    computing a photogrammetric orientation solution using the elevation value data obtained from the elevation model and the imagery data expressed in world coordinates;    performing a pixel intensity interpolation operation using the results of the photogrammetric solution and perspective image data; and    using the results of the pixel intensity interpolation operation and the imagery data expressed in cartographic coordinates to produce an orthophoto expressed in cartographic coordinates.    
   
   
       10 . The method according to  claim 9 , wherein the elevation model includes a first source of elevation model data and a second source of elevation model data; and including the steps of prioritizing the accessing of the first and second sources of elevation model data; and accessing the first and second sources of elevation model data in the order of priority