|MAPC2MAPC Help pages : Large TIF files
program tries to load an image into memory. The image is held as its
original bit depth but some functions - such as warp - will create a
second copy at 24bits per pixel.
Starting with version 460, there is the option to handle large TIF images as 'virtual storage'. This expands the size of maps that can be handled - 5Gigapixels is possible - but there are some restrictions:-
- Performance is much slower because of the extra hard disk activity.
- Edit functions Rescale and Crop are supported as long as the resulting image can be held in memory.
- Edit functions that change the map - Darken, Load Track, Sharpen, Warp - are not supported
- The original map cannot be saved.
- All other outputs are possible - including those, like Mobile Atlas, which imply a warp (reprojection).
The TIF files that can be handled include those created by GDAL_Translate from, for example, ECW files. Irfanview will also convert many image formats to TIFF but does not retain calibration. The BigTiff format (files > 4GB) is not supported. From version 518, both Stripped and Tiled TIF files are supported.
To enable this functionality us Edit>Preferences and check 'Use VS for TIFF files'. The VS tile size determines the size of the pieces of map that are written to disk and retrieved as needed. 1024 seems to work for most purposes. Increasing it may improve speed but at the risk of running out of memory.
Starting with version 502 there is limited processing of files that are too big to process because the intermediate TIFF file is greater than 4GB. This is implemented as a utilty function : Utilities>Convert Huge Map to Mobile Atlas. This processes the map in sections to build up a seamless set of tiles as z/x/y.png (OSM Tracker) format. This can then be used by Mobile Atlas Creator to make a variety of formats or by MOBAT2JNX to make a JNX file. You will need to provide the projection with the usual TFW dialogue. To facilitate the use of Mobile Atlas Creator, a .XML file is created - copy this to the Mapsources folder.