If a gap or shift is noticed in a mosaic created by GeoExpress, it is likely that the input images are not rectified to a consistent pixel-grid, though it could also be that the georeferencing was originally incorrect. In these cases you must consult your image provider.
Several other potential causes of this issue are:
- GeoExpress is reading input georeferencing from world files when it should not be, or not reading input georeferencing from world files when it should be. (In older versions of GeoExpress, world files were used by default if present. Currently, world files are ignored unless you specify that they should be used to override native georeferencing.)
- There is rotation in the source tiles.
First, check to see whether there are world files present with updated information that should be used. If world files are present and they should be used, select the Allow world files to override native georeferencing checkbox. To find the checkbox choose Encode Options from the Options menu and select the Input tab. (In older versions of GeoExpress this checkbox is selected by default). If world files are present but they should not be used, make sure the checkbox is clear.
If you selected or cleared the Allow world files to override native georeferencing checkbox, reencode your mosaic and examine the results to see whether this solves the gap problem. If it does, you’re finished.
If there were no world files or the above course of action does not solve the problem, use the command line tool mrsidgeoinfo to learn whether your source tiles are rotated.
Versions 8.5 and earlier of GeoExpress do not support image rotation, but if there is rotation in your source tiles a viable workaround is to create a new mosaic with multiple projection systems enabled. Doing this applies a reprojector to each tile even when the tiles are not being reprojected from one coordinate reference system to another.
Beginning with version 9, GeoExpress reads image rotation metadata and creates rotated output images by default.
To create a new mosaic with multiple projection systems enabled:
- Click the Create New Mosaicicon on the toolbar.
- In the dialog that appears select the Allow multiple projection systems
- Proceed with your normal workflow and encode.
If there is no rotation, the problem is likely with the original georeferencing of the source tiles.