Gamma DIFF&GEO: Reference Manual

coord_trans

ANSI-C program: coord_trans.c

NAME
coord_trans - Coordinate transformation between map projections for single coordinate.

SYNOPSIS
coord_trans

EXAMPLE
coord_trans

Starts coordinate transformation between map projections for single coordinate. (interactive)

DESCRIPTION
coord_trans transforms a single coordinate from the input map projection to the output map projection.

The definition of the input and output projections is interactive. The supported map projections are listed in a table below.

The map projection definition is supported with the projection information available in the lists datums.h, ellipsoids.h, projection_params.h. Apart from the selection of predefined values out of these lists the user has the option to define each of the parameters.

In a first step the input map has to be defined. This definition includes:
- the ellipsoid used
- the Datum shift of this ellipsoid relative to WGS84
- the map projection type
- the parameters required to specify the map projection
- the definition of the selected DEM/map section (corner coordinates, spacing, DEM/map dimension)

Then the input coordinates, i.e. nothing and easting (or longitude and latitude) are indicated.

Next the output map has to be defined. This definition includes again:
- the ellipsoid used
- the Datum shift of this ellipsoid relative to WGS84
- the map projection type
- the parameters required to specify the map projection
- the definition of the selected DEM/map section (corner coordinates, spacing, DEM/map dimension)

Now, with the required information available, coord_trans converts the specified input coordinates to the output map coordinates.

coord_trans tries to combine high flexibility with strong user support. On one hand the user has the option to define each of the required parameters. On the other hand often used ellipsoids, Datum shifts, and projection parameter sets are proposed to the user. This allows the user, for example, to specify the national coordinates used by a specific country without having to search for the detailed parameter values, elsewhere.

The different DEM/map coordinate systems which are supported are:

The DEM/map geometry definition is done as follows:

First the user is asked to select one of the above mentioned DEM/map coordinate systems. Then a country name such as United Kingdom, USA, Germany, or other allows to search the lists for specific parameter sets for the selected countries. If the desired parameters are not found in the lists the user may want to select other to define the parameters.

Based on the indicated country name a list of Datums and Ellipsoids are offered (containing at least WGS84). The user can select one of the Datum/Ellipsoid sets by indicating the corresponding row number.

Next the projection parameters are specified. Again the user may enter a country name (typically the same as specified before) or other to either select a projection parameter set out of a list proposed for the selected country or to specify these parameters without such a list.

After the specification of the ellipsoid, Datum, and projection parameters the remaining parameters including the DEM/map name, the DEM data format, the DEM height offset, the DEM height scale factor, the DEM/map width and number of lines, the corner coordinates (easting/northing resp. longitude/latitude), and the pixel spacing in the two directions.

In addition, the output (transformed) coordinates lat/lon for EQA resp. nothing/easting for the other projections are written to standard output.

SEE ALSO
datums.h, ellipsoids.h, projection_params.h, typedef_ISP.h, typedef_DIFF.h .

© Copyrights for Documentation, Users Guide and Reference Manual by Gamma Remote Sensing, 2013.
UW, CW, last change 8-Mar-2013.