Gamma DIFF&GEO: Reference Manual

gc_map_fine

NAME
gc_map_fine - Geocoding lookup table correction using offset polynomials from the DIFF parameter file.

SYNOPSIS
gc_map_fine <gc_in> <width> <DIFF_par> <gc_out> [ref_flt]

<gc_in>	(input) geocoding lookup table
<width>	(input) width of lookup table (samples)
<DIFF_par>	(input) DIFF/GEO parameter file containing fine registration polynomial coefficients
<gc_out>	(output) (output) refined geocoding lookup table
[ref_flg]	offsets are relative to the reference image for offset determination. 0: actual SAR image reference, 1: simulated image reference (default)

EXAMPLE
gc_map_fine 19960621.lt0 1422 19969621.diff_par 19960621.lt1

Applies the fine registration function to the input lookup table to create the refined output lookup table which characterizes the refined geocoding transformation in a single step. In this example the simulated SAR image is used as reference.

DESCRIPTION
gc_map_fine applies the fine registration function to the input lookup table to create the refined output lookup table. This is done by addition of the fine registration offsets to the lookup vectors. For geocoding and differential interferometry using a simulated image for correction, as default the simulated SAR image is the reference image in the estimation of offsets. In the case where the user has selected the SAR image as the reference, the reference image option to the gc_map_fine command must set to 0.

The resulting complex valued geocoding lookup table describes the complete geocoding transformation (including the fine registration). For subsequent geocoding of data from SAR geometry to map geometry or reverse mapping, this has the advantage that the geocoding can be done in a single step. The use of a single resampling operation in the geocoding improves the quality of the geocoded products and increases the geocoding efficiency.

The initial geocoding lookup table can be derived based on a DEM in map geometry and the SAR imaging geometry using the program gc_map or gc_map_grd. The fine registration function (bilinear polynomial for registration offsets) can be found using the DIFF&GEO image registration programs init_offsetm and offset_pwrm. For the later use of the fine registration function for the refinement of the lookup table the default situation is that the simulated SAR image is used as the reference geometry, i.e. the offsets of the actual SAR image relative to the simulated SAR geometry are determined.

The refined geocoding lookup table is used by the programs geocode and geocode_back for forward and backward geocoding. Once the refined lookup table is determined the initial lookup table should no longer be used.

The refined geocoding lookup table may be inverted using the program gc_map_inversion.