Gamma ISP: Reference Manual

grasses

ANSI-C program: grasses.c

NAME
grasses - Unwrapping of the interferometric phase based on the complex valued interferogram, the phase unwrapping flag file, and, if existing, the already partially unwrapped phse file.

SYNOPSIS
grasses <int> <flag> <unw> <width> [xmin] [xmax] [ymin] [ymax] [xinit] [yinit] [init_ph_flag]

<int>	interferogram filename (fcomplex)
<flag>	unwrapping flag filename (char)
<unw>	unwrapped phase filename (float)
<width>	number of samples/row
[xmin]	offset to starting range pixel (default = 0)
[xmax]	offset last range pixel (default = width-1)
[ymin]	offset to starting azimuth row, relative to start (default = 0)
[ymax]	offset to last azimuth row, relative to start (default = nlines-1)
[xinit]	starting range pixel for unwrapping (default = width/2)
[yinit]	starting row to unwrap (default = height/2)
[init_ph_flag]	flag to set phase at starting point to 0.0 (default 0: not set to 0.0, 1: set to 0.0)

EXAMPLE
grasses 1352_1610.flt.sm 1352_1610.flag 1352_1610.unw 2500

Unwraps the filtered complex interferogram 1352_1610.flt.sm starting the unwrapping at the image center.

grasses 1352_1610.flt.sm 1352_1610.flag 1352_1610.unw 2500 0 2499 0 4800 1200 4000 1

Unwraps the filtered complex interferogram 1352_1610.flt.sm starting at pixel number (1200,4000). The phase at the starting location is set to 0.0 (to facilitate consecutive scaling of multiple unwrapped phase images).

grasses 1352_1610.flt.sm 1352_1610.flag035 1352_1610.unw 2500
followed by
grasses 1352_1610.flt.sm 1352_1610.flag020 1352_1610.unw 2500
Unwraps in a first step the filtered complex interferogram 1352_1610.flt.sm using the flag file 1352_1610.flag035 (generated using a coherence threshold of 0.35). In a second step the already unwrapped phase image is read together with the flag file 1352_1610.flag020 (generated using a coherence threshold of 0.20), to increase the unwrapped area. Values already unwrapped in the first round are kept and used as starting points to continue the unwrapping in the second round. This process can be continued.

DESCRIPTION
grasses reads the smoothed interferogram, the phase unwrapping flag file, and, if existing, the provided unwrapped phase image, and unwraps the interferometric phase using the tree structure saved in the flagfile to constrain a region filling algorithm. The unwrapping starts at a user defined location, nominally the center of the image. The program keeps track of the unwrapped area. Once the unwrapped area is surrounded by lines that cannot be crossed, these are the border of the data and branches of the trees it stops.

After the unwrapping of a region stopped, bridge supports the continuation of the phase unwrapping in the remaining disconnected areas not unwrapped yet. Once unwrapped, the image is written to a file. For each pixel a flag of 8 bits is stored. The meaning of the individual bits is explained in the typedef_ISP.h file. The phase unwrapped interferogram can be displayed using the program disrmg or written to a SUN rasterfile using rasrmg.

The information contained in the flagfile can be displayed with the program disflag or as a SUN raster or BMP format image using rastree.

As a way to optimize the trade off between the maximization of the unwraped area (or minimization of the not unwrapped gaps) and the maximization of the confidence in the phase unwrapping (or minimization of phase unwrapping errors) we recommend to run grasses multiple times with different flag files which were determined with different coherence thresholds.

If the unwrapped phase file indicated on the command line is already existing the program reads it and modifies the indicated flag file to mark the already unwrapped area. The unwrapping process is continued for the remaining area only. The user has the option to set the phase for the starting location to 0.0. This feature can be useful for the combination of multiple unwrapped phase images over the same area.

SEE ALSO
typedef_ISP.h, bridge disflag, rasrmg, disrmg, rastree.