Method for creating a mosaic image using masks
View Patent ↗Photographic images recorded with mobile mapping vehicles ( 20 ) in real life situations usually contain cars or other moving objects ( 34 ) that cover visual information on the road surface ( 24 ). According to the techniques of this invention, moving objects ( 34 ) are detected by grayscale differencing in overlapping pixels or sections of two or more orthorectified image tiles. Based on moving object identification, masks are generated for each orthorectified tile. The masks are then compared and priorities established based on grayscale values associated with the masks. Mosaics of a large surface of interest such as the Earth can be assembled from a plurality of overlapping photographic images with moving objects ( 34 ) largely removed from the resulting mosaic.
1. A method for creating a mosaic of a large surface of interest such as the earth from a plurality of small, overlapping photographic images, said method comprising the steps of:
providing a first tile from a first orthorectified photograph of the surface of interest, the first photograph having been taken with a first camera at a first distance and at a first time, the first tile divided into discrete sections and associated with an absolute coordinate location and orientation relative to the surface of interest;
providing a first mask for the first tile in which any known moving foreground objects are assigned low priority grayscale values and all other areas in the first tile are assigned a high priority grayscale value, the first mask being divided into discrete sections corresponding to the sections of the first tile;
providing a second tile from a second orthorectified photograph of the surface of interest at least partly overlapping the first tile, the second photograph having been taken with a second camera at a second distance and at a second time, the second time being different from the first time, the second tile divided into discrete sections and associated with an absolute coordinate location and orientation relative to the surface of interest;
predicting when any known moving foreground object in the first tile will be visible by the second camera;
creating a second mask for the second tile in which any known moving foreground objects are assigned low priority grayscale values and all other areas in the second tile are assigned a high priority grayscale value, the second mask being divided into discrete sections corresponding to the sections of the second tile, wherein the second mask is generated based on the first mask, the prediction, and a disposition and heading of the first and second camera;
comparing coincident sections in the first and second tiles; and
replacing the coincident section in the first tile with the coincident section from the second tile if the grayscale value of the corresponding section in the second mask has a higher priority than the grayscale value of the corresponding section in the first mask.
2. The method of claim 1 further including the step of replacing the coincident section in the first tile with the coincident section from the second tile if there is no corresponding section in the first tile.
3. The method of claim 1 further including the step of replacing the coincident section in the first tile with the coincident section from the second tile if the grayscale value of the corresponding section of the second mask is equal to the grayscale value of the corresponding section of the first mask and the second photograph distance is smaller than the first photograph distance.
4. The method of claim 1 wherein said step of replacing the coincident section in the first tile with the coincident section from the second tile includes replacing the corresponding section in the first mask with the corresponding section in the second mask, and replacing the first photograph distance with the second photograph distance.
5. The method of claim 1 wherein said steps of providing the respective first and second tiles include mounting at least one camera on a mobile vehicle that moves relative to the surface of interest.
6. The method of claim 1 wherein said steps of associating the first and second tiles include imprinting coordinate data from a GPS satellite receiver on the respective first and second tiles.