Gamma DIFF&GEO: Reference Manual

DEM_par

DEM parameter file (for structure definition see typedef_DIFF.h)

NAME
DEM_par - Digital Elevation Model (DEM) parameter file (text format) used by Gamma DIFF&GEO software.
This can also contain a description of the projection used for image or parameter data

EXAMPLE and PARAMETER DEFINITIONS
The format of the DEM parameter file is different for different DEM projections. Supported DEM projections are:

Keyword	Projection
EQA	Equiangular
UTM	Universal Transverse Mercator
TM	Transverse Mercator
OMCH	Oblique Mercator (Switzerland)
LCC	Lambert Conformal Conic (France)
PS	Polar Stereographic
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)
PC	Polyconic Projection
AEAC	Albers Equal Area Conic
LCC2	Lambert Conformal Conic Projection (Secant solution, Belgium)
OM	Oblique Mercator
HOM	Hotine Oblique Mercator

The parameter definitions are not the same for the different coordinates, but most parameters are common to all projections.

The parameters contained in the DEM/map parameter file are structured into:
- general parameters
- ellipsoid parameters
- datum parameters
- projection parameters.

Part 1: General Parameters

Keyword	Example	Definition
title	Death Valley UTM DEM	Title, name, identification for DEM
DEM_projection	UTM	Universal Transverse Mercator
data_format	REAL*4	DEM data format; valid formats are REAL4 (4-byte floating point) and INTEGER2 (2-byte, short integer)
DEM_hgt_offset	0.00000	Height offset in units
DEM_scale	1.0	Height scale used in DEM in meter/unit
width	2000	DEM width in pixels
nlines	2000	DEM number of lines
corner_north	4095800.000	Northing of first DEM pixel (m)
corner_east	477300.000	Easting of first DEM pixel (m)
post_north	-100.0000000	DEM posting (pixel spacing) North direction; negative numbers indicate that DEM lines are listed from North to South
post_east	100.0000000	DEM posting (pixel spacing) East direction; negative numbers indicate that DEM

In the case of EQA coordinates the last four lines are replaced by:

Keyword	Example	Definition
corner_lat	37.0000000	Latitude of first DEM pixel (decimal degrees)
corner_lon	-117.2500000	Longitude of first DEM pixel (decimal degrees, values between -180 and 180)
post_lat	-8.3333000e-04	DEM posting (pixel spacing) in latitude; negative numbers indicate that DEM pixels are listed from North to South
post_lon	8.3333000e-04	DEM posting (pixel spacing) in longitude; negative numbers indicate that DEM pixels are listed from East to West

In the case of PS coordinates the following parameter is added:

Keyword	Example	Definition
PS_secant_lat	71.0000000	latitude of the secant plane with no distortion, +/-71 degrees for N. or S. hemispheres respectively

Part 2: Ellipsoid Parameters

Keyword	Example	Definition
ellipsoid_name:	Airy 1830	Ellipsoid name (from list or specified by user)
ellipsoid_ra	6377563.396 m	Ellipsoid semi-major axis in meter
ellipsoid_reciprocal_flattening	299.3249646	Ellipsoid reciprocal flattening (i.e. 1/f)

Notice, other ellipsoid parameters, such as the ellipsoid semi-minor axis, are calculated from the two specified parameters.

Part 3: Datum Parameters

Keyword	Example	Definition
datum_name:	United Kingdom National	Datum name (from list or specified by user)
datum_shift_dx	370.300 m	Datum shift in x direction (Cartesian coordinates) relative to WGS84
datum_shift_dy	-111.060 m	Datum shift in y direction (Cartesian coordinates) relative to WGS84
datum_shift_dz	431.170 m	Datum shift in z direction (Cartesian coordinates) relative to WGS84
datum_scale_m	0.00000e+00	Datum shift scale m parameter, (1+datum_scale_m) is the scale factor
datum_rotation_alpha	0.00000e+00 arc-sec	Datum rotation angle alpha (around x axis) in arc-seconds
datum_rotation_beta	0.00000e+00 arc-sec	Datum rotation angle beta (around y axis) in arc-seconds
datum_rotation_gamma	0.00000e+00 arc-sec	Datum rotation angle gamma (around z axis) in arc-seconds
datum_country_list	United Kingdom, England, Great Britain	Datum country list (included in datums.h list for parameter set selection

Notice, with the Datum Shift definition used the datum_shift_dx, datum_shift_dy, datum_shift_dz, indicate the coordinates of the origin of the local ellipsoid relative to the WGS84 Datum (in Cartesian coordinates). Both 3 and 7 Parameter Datum definitions are supported.

Part 4: Projection Parameters for UTM, TM, OMCH, LCC, PS, PC, AEAC, LCC2, OM, HOM coordinates

Keyword	Example	Definition
projection_name	TM - United Kingdom, England	Projection name (from list or specified by user)
projection_zone	0	Zone number (0 in the case of one single zone)
false_easting	400000.000 m	False Easting [m]
false_northing	-100000.000 m	False Northing [m]
projection_k0	0.9996013	Scale factor k0 used by the projection
center_longitude	-2.0000000 decimal degrees	Center longitude in decimal degrees (-180...180)
center_latitude	49.0000000 decimal degrees	Center latitude in decimal degrees (-90...90)

In the case of SCH projection, the following projection keywords are used:

Keyword	Example	Definition
SCH_peg_lat		SCH peg point latitude (degrees)
SCH_peg_lon		SCH peg point longitude (degrees)
SCH_heading		SCH heading (degrees)
SCH_corner_s		SCH corner offset from peg point s (m)
SCH_corner_c		SCH corner offset from peg point c (m)
SCH_post_s		SCH posting along track s (m)
SCH_post_c		SCH posting along track c (m)

DESCRIPTION
The DEM_par contains parameter values to describe the elliposoid, datum and projection of DEM and map data. The DEM_par file is generated using the program create_dem_par. The user is interactively asked for the input used to describe a DEM or map. A variety of projections are supported.

The data structures contained in the DEM_par are defined in the in DIFF type definition file typedef_DIFF.h. The data values are stored as keyword: value pairs.