World Reference File
World files contain the affine relationship between source image coordinates (pixel locations) and real-world reference coordinates (lat/long or other real-world coordinate units). World files contain a computed relationship between source image coordinates and reference coordinates and not the complete reference point information.
Reference points cannot be reloaded from a world file because they do not exist in the file. When a world file is loaded into the reference point list the 4 corners of the source image are recalculated using the world file parameters and are displayed as reference points.
Tagged Image File Format (TIFF or TIF) is one of the most common geospatial image formats. Many images from a variety of GIS systems are stored in this format. A GeoTIFF is a TIFF file with embedded geographic information identifying its position and scale in world coordinates. It uses an ASCII header that contains all of the referencing information. These headers are automatically loaded into Didger when the source image is opened. Didger immediately recognizes that the image is georeferenced. Unlike other world files, GeoTIFFs do not require a separate reference file.
The Blue Marble Reference Settings File saves the complete reference point list information so that it can be loaded again in the future. Within a Blue Marble Reference File, the first line contains the version of the file format (not to be confused with the version of the software) and the total number of points in the file. The remaining lines contain the point ID, the x (row) pixel, the y (column) pixel, the z (elevation) value which is usually 0.00 followed by the ground coordinates expressed as Latitude or Northing (Y), Longitude or Easting (X) and Elevation (Z). The last value indicates whether the point described on that line is included in the solution, 0 = not included and 1 = included. It is recommended that a Blue Marble Reference file also be saved when saving a world file so that the raw reference point information can be recalled at a later date. Coordinate system information may be stored in an rsf file.
ESRI World files are text-based files containing spatial reference information. Various Environmental Sciences Research Institute (ESRI) programs and other programs import the information in this file. The first and third characters of the image file extension, plus a final "w," are used as the world file extension. For example, IMAGE.TIF would have an associated world file called IMAGE.TFW.
ESRI .prj files are text files associated with an ArcInfo coverage, GRID, or TIN. The PRJ file contains the coordinate system information for the data. In a more general sense, PRJ can refer to the coordinate system of data even if the information is not stored in a PRJ file. For example, the PRJ of a shapefile could be WGS 1984 UTM zone 15 north.
Golden Software Reference files contain the projection settings used to project the boundary in Didger. Projection, datum, and georeference information are stored in the .GSR2 file. When you import a boundary that has an associated .GSR2 file into Didger, the projection information is used when displaying the map even though the file format does not support projections. If the Golden Software Reference file is deleted, the boundary can be imported but you must supply the projection information during import.
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