Projection

Projection information is a set of parameters, defining the relation between a local grid and a geographical coordinate system.

For multiple grid file formats the projection information is read from the grid files or accompanying world files (a GeoTiff file for example often has this information stored in a .tfw file in the same folder).

The projection information can also be explicitly configured in the GeoDMS configuration, see: geographic grid domain.

The projection is presented in the GeoDMS GUI > Detail Pages > General > Projection for the geographic domain unit and all attributes with this domain unit.

contents

Projection information consists of the following set of parameters:

• pixel size in the x-direction in map units, often positive
• pixel size in the y-direction in map units, often negative
• x-coordinate of the center of the upper left pixel
• y-coordinate of the center of the upper left pixel

A world file can also contain rotation information. gdal.grid uses it. Since GeoDMS 20.22.0 the tiff and bmp StorageManagers refuse it: a rotated GeoTIFF, or a world file with rotation terms, read into a grid domain that takes its georeference from the file stops with an error that names gdal.grid. Before, they dropped the rotation without a message and placed the grid as if it were axis-aligned. Reading only the values of such a file, into a domain without a georeference, still works. Since GeoDMS 20.22.0 gdal.grid applies such a rotation in the right orientation. Before, it transposed every rotated georeference, so a rotated grid got the wrong world coordinates.

Since GeoDMS 20.22.0 a grid with a rotated or sheared georeference cannot be written, neither with gdalwrite.grid nor to the world file that the tiff and bmp StorageManagers write next to a grid: the write stops with the error writing ...: a rotated or sheared grid georeference cannot be written yet. Before, such a grid was written as if it were axis-aligned, with a wrong georeference and without an error.