Raster Files — Guidelines and Restrictions

Projections

AIR has certified various projections as described in the Projections topic.

File Size

The following table summarizes file size restrictions:

Cell Value Type

Raster datasets represent geographic features by dividing the world into discrete square or rectangular cells laid out in a grid. Each cell has a value that is used to represent some characteristic of that location, such as temperature, elevation, or a spectral value. Touchstone supports various cell values based on the raster file format. For supported values, refer to the individual page for each supported format

Bands

Some rasters have a single band while others have multiple bands. Basically, a band is represented by a single matrix of cell values while a raster is represented by multiple bands that contain multiple, spatially coincident matrices of cell values representing the same spatial area. For example, a true color orthophoto is a multiband image that has three bands, where each band represents red, green, or blue light. In Touchstone, you can import only one band at a time of the multiband image as a custom map layer; you select each band from a list in the Map Layer Import user interface.

Pyramids

Raster pyramids are lower-resolution (downsampled) images of the original data whose purpose is to improve display speed and performance. Each pyramid level covers the entire raster dataset, and you can specify the number of levels to generate. Touchstone requires raster pyramids to be built correctly in order to improve display speed and performance. Rasters with pyramids will be imported directly; otherwise, Touchstone will generate the pyramids for the imported rasters automatically during Map Layer Import.

Before importing raster files with pre-generated pyramids, you may want to make sure that the pyramids are properly generated for the file; otherwise, you may see slowness in visualization and analysis.

When you try to import a raster file that does not have pre-built pyramids, Touchstone will try to generate the pyramids for the raster file. If the raster file has a width or height larger than 65,535 pixels, Touchstone will not generate the pyramids out of concern for the increase in processing time. The import will fail and you should build pyramids outside of Touchstone and then import the data.