Gamma DIFF&GEO: Reference Manual

create_dem_par

NAME
create_dem_par - Create DEM/map projection parameter file used by DIFF&GEO package

SYNOPSIS
create_dem_par <DEM_par> [SLC_par] [terra_alt] [delta_y] [delta_x]

<DEM_par>	(input/output) DIFF/GEO DEM parameter file
[SLC_par]	(input) ISP SLC/MLI image parameter file
terra_alt	nominal terrain altitude, default: 0.0 m.
delta_y	DEM Y line spacing for a new DEM_par file geographical coordinates (EQA projection latitude) default: -5.00e-04 deg. all other map projections default: -50.000 m.
delta_x	DEM X sample spacing for a new DEM_par file geographical coordinates (EQA projection longitude) default: 5.00e-04 deg. all other map projections default: 50.000 m.

EXAMPLE
create_dem_par Landers_EQA.dem_par 19990421.slc.par

Generates a DEM_parameter file, default posting is -5.0e-4 degrees (northing) and 5.0e-4 degrees easting if EQA geoegraphical projection is selected. The default terrain altitude for calculation of the image bounds is 0.0 meters.

create_dem_par Landers_UTM.dem_par 19990421.slc.par 500.0 -25.0 25.0

Generates a DEM_parameter file, default posting is -25 meters northing and 25 meters easting if any projection other than EQA selected. The default terrain altitude for calculation of the image bounds is 500.0 meters.

DESCRIPTION
create_dem_par supports the interactive creation of a DEM/map parameter file (a) for an existing digital elevation model (DEM), or (b) for the definition of a new map geometry to be used, for example, for ellipsoid corrected geocoding and terrain corrected geocoding.

The DEM parameter file characterizes:
- the ellipsoid
- 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 dimensions)

create_dem_par 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, to specify the national coordinates used by a specific country without having to search for the detailed parameter values elsewhere.

The supported DEM projections are :

Keyword	Projection
EQA	Equiangular
UTM	Universal Transverse Mercator
OMCH	Oblique Mercator (Switzerland)
LCC	Lambert Conformal Conic (France)
TM	Transverse Mercator
PS	Polar Stereographic
LCC2	Lambert Conformal Conic of Belgium, Madagaskar
PC	Polyconic Projection
AEAC	Albers Equal Area Conic
SCH	Spherical geometry map projection (see "Zebker et. al, "Geodetically Accurate INSAR Data Processor", Trans. Geoscience and Remote Sensing, pp.4309-4321, vol. 49, no. 12, Dec., 2010)

The user is interactively queried for the required DEM parameters. The format of the DEM parameter file depends on the coordinate system of the DEM. Different projections require different parameters values. The exact definitions and formats of the individual parameters are specified in dem_par. The DEM data itself can be either 4-byte/value floating point or 2-byte/value short integer format.

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 North-West corner coordinates (easting/northing resp. longitude/latitude), and the pixel spacing (posting) in the two directions. The posting in the north direction is always < 0.0 and east posting must always be > 0.0. . Data line order must be from North to South, and sample order from West to East.

When creating a DEM/map parameter file an SLC/MLI image parameter file may be specified. In this case the bounds of the DEM map are proposed the enclose the image if the DEM_par does not yet exist. A additional border is added all around the map to ensure that the image is enclosed, even if there are large variations in terrain height. This border is 5000m or .05 deg in width depending on the projection coordinates. The width and height of the enclosing DEM are calculated from the image bounds. In the case of EQA coordinates, the default line and sample spacing is 0.0005 deg. and for all other projections the default spacing is by default 50 meters. The y line spacing and x sampling coordinate spacing must be specified on the command line for new DEM parameter files.

OPTIONS
To specify a DEM/map parameter file with country, not contained in the list, specify "other". To specify custom ellipsoid parameters, enter 0 for the ellipsoid number.