ANSI-C program: fspf_pt.c
NAME
fspf_pt - Fast spatial filter for point data (single record or
all records)
SYNOPSIS
fspf_pt <plist> <pmask> <SLC_par>
<pdata_in> <pdata_out> [rec_num] [type] [r_max]
[spf_type] [msk_flag]
| <plist> | (input) point list (int) |
| <pmask> | (input) point data stack of mask values (uchar, set to - to accept all points) |
| <SLC_par> | (input) SLC parameter file of point list coordinates |
| <pdata_in> | (input) point data stack (various types supported) |
| <pdata_out> | (output) spatially filtered point data stack (same type as pdata_in) |
| [rec_num] | record number in pdata_in and pdata_out to process (default -: all records) |
| [type] | data type (0:fcomplex 1:scomplex 2:float, default -: float) |
| [r_max] | maximum radius (range samples, default: 64 ) |
| [spf_type] | spatial filter type 0: uniform average (default for fcomplex and scomplex data) 1: triangular weighted average: 1 - (r/r_max) 2: quadratic weighted average: 1 - (r/r_max)**2 3: Gaussian weighted average: exp(-2.*(r**2/r_max**2)) 4: linear least-squares (default for float data) |
| [msk_flag] | output mask flag 0: output only for points specified in the point mask (default) 1: expand filtered data to entire point list |
EXAMPLE
fspf_pt pt pmask1 08256.rslc.par pdiff0 pdiff0.spf 14 0 500
2 1
Same as above except that (1) the filtering is performed for all data records of the point stack and that (2) the solution is not expanded to the entire point list and that (3) data type is float.
INSTALLATION
Source code fspf_pt.c in ./IPTA/src, executable version fspf_pt
in ./IPTA/bin
DESCRIPTION
In the estimation of orbital phase trends and long-wavelength
atmospheric path delays spatial filtering with large filter
windows is frequently applied in an IPTA processing. Using spf_pt
such filtering is supported, but in the case of very large
windows it is very slow. The main objective of the program
fspf_pt is to provide a useful alternative for such filtering
which is computationally much more efficient. fspf_pt can be used
for both complex valued point interferograms (e.g. pdiff obtained
after subtracting of the simulated topographic phase, or
re-wrapped residual phases from a regression analysis) or float
data (residual phases, atmospheric path delays).
fspf_pt supports a fast spatial filtering of point data
stacks. Either one or all records can be filtered. The points to
be considered in the filtering can be indicated through the
spatial radius (indicated in range samples).
The functionality of fspf_pt is essentially similar (except
reference point bias removal) to spf_pt, however, the spatial filtering is
performed for large filter windows within a much shorter program
execution time. The speedup is obtained via a two-step approach
consisting of an unweighted multilooking and a weighted spatial
filtering of the multilooked data.
Using fspf_pt with small window sizes is not recommended (use
spf_pt instead).
If a point mask is indicated only the values listed in the
mask as valid points are considered in the filtering.
Nevertheless, filtered (interpolated) values can be written out
to all other points, as well, if the output mask flag is set to
1.
Either one record or all records can be filtered. To select
all records in the stack enter "-" for the record number.
Different format types (0:fcomplex 1:scomplex 2:float, default -:
float) are supported. The format of the output point data stack
with the filtered values has the same type as the input point
data stack.
The SLC parameter file associated with the point list
coordinate geometry is required to calculate ground distances
between pairs of points. Such distances are calculated using the
ground range sampling (calculated from slant range sampling and
incidence angle) and the azimuth spacing. The maximum search area
radius is indicated in SLC range samples. Only valid points, i.e.
points with a non-zero value in the mask are considered. For
points with a zero in the mask the output is set to the NULL
value, unless the output mask flag is set to 1.
For the spatial filtering constant weights, a linearly
decreasing ramp (linear with ground distance), a quadratic, or a
Gaussian distance-weighed average can be selected. Points with
NULL values in the input data are not considered in the
filtering. For float data values, filtering based upon a
least-squares planar fit to the data values is the default
filtering method (spf_type = 4). This gives a better estimate of
the filtered data when the data points are not uniformly
distributed over the search region, e.g. at the edges of
data.
OPTIONS
none.
SEE ALSO
fspf_unw_pt, spf_pt.
© Copyrights for Documentation, Users Guide and Reference Manual by Gamma Remote Sensing, 2011.
UW, CW, OF,
last change 28-Nov-2011.