ANSI-C program: bridge.c
NAME
bridge - Phase unwrapping of disconnected areas using user
defined bridges.
SYNOPSIS
bridge <int> <flag> <unw>
<bridge> <width> [xmin] [xmax] [ymin]
[ymax]
| <int> | (input) interferogram (fcomplex) |
| <flag> | (input) unwrapping flag file |
| <unw> | (input/output) unwrapped phase (float) |
| <bridge> | (input) bridge data file (text format) |
| <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) |
EXAMPLE
bridge 1352_1610.sm 1352_1610.flag 1352_1610.unw
1352_1610.bridges 2500
DESCRIPTION
bridge reads smoothed interferogram, flagfile, the unwrapped
phase (unwrapped previously using grasses) and the bridges file (containing
location coordinates of starting and ending location of bridges
and expected multiple of 2PI phase offset between the two
locations).
The format of the bridges file is found here below:
| column number of unwrapped pixel | row number of unwrapped pixel | column number of wrapped pixel | row number of wrapped pixel | multiples of 2PI to add or subtract. For example a value of 0 means that the phases at the start and end of the bridge are within PI |
An example for a bridges file is found here below:
| 712 | 1148 | 710 | 1160 | 0 |
| 840 | 1210 | 830 | 1208 | 0 |
| 488 | 800 | 501 | 790 | 1 |
The bridges file is manually edited. The determination of the coordinates of the wrapped and unwrapped pixel which shall be connected by bridges is supported by the program rastree which generates a SUN raster file or BMP file showing the wrapped and unwrapped phases (the wrapped ones in darker colors). This SUN raster file can be displayed using disras and the coordinates found by clicking the desired locations.
bridge restarts unwrapping of the interferometric phase at the end of each bridge with an unwrapped phase differing by less than PI from the multiple of 2PI of the start of the bridge plus the indicated multiple of 2PI phase offset. 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. To unwrap the entire image it might be necessary to define additional bridges and run bridge again.
The file containing the unwrapped phase is updated with the additionally unwrapped phases. For data security reasons it is recommended to backup the unwrapped phase file before running bridge. The information on the unwrapped areas is written into the flagfile. 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 raster file or BMP format image using rasrmg. The information contained in the flagfile can be displayed with the program disflag or presented as a SUN raster or BMP format image using rastree.
SEE ALSO
typedef_ISP.h, grasses.h, disflag, rasrmg, disrmg, rastree