GAMMA Interferometric Point Target Analysis Software (IPTA): Reference Manual

spf_pt

ANSI-C program: spf_pt.c

NAME
spf_pt - spatial filter and reference point bias removal for point data (single record or all records)

SYNOPSIS
spf_pt <plist> <pmask> <SLC_par> <pdata_in> <pdata_out> [rec_num] [type] [r_max] [spf_type] [np_max] [pt_num] [mode]

<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)
[spf_type ]	spatial filter type 0: uniform average (default for fcomplex and scomplex data) 1: triangular weighted average 2: linear least-squares (default for float data))
np_max	maximum number of neighbor points in the filter (default 32, -: all points within search radius)
[r_max]	maximum radius (range samples, default: 64)
[w_func]	radial weighting function (0: 1.0 1: 1.0-radius/r_max)
[np_max]	maximum number of neighbor points in the filter (default - : all points within search radius)
pt_num	point number for local filtering about a single point (beginning with 0)
mode	processing mode (default=0:spatial filtering 1:reference point bias removal)

EXAMPLE
spf_pt testsite.plist testsite.pmask 08256.rslc.par testsite.punw1 testsite.punw2 14 2 25 1 12

Conducts a spatial filtering of record 14 of the point data stack testsite.punw1. Points within a radius of 25 SLC range samples are identified, ordered by distance, and the nearest 12 (or fewer) used for the spatial filtering.

spf_pt testsite.plist testsite.pmask 08256.rslc.par testsite.punw1 testsite.punw2 - 2 25 1 -1

Conducts a spatial filtering of all records of the point data stack testsite.punw1. All points within a radius of 25 SLC range samples are considered in the spatial filtering.

spf_pt testsite.plist testsite.pmask 08256.rslc.par testsite.punw1 testsite.punw2 - 2 200 1 12

Conducts a spatial filtering of all records of the point data stack testsite.punw1. Points within a very large radius (of 200 SLC range samples) are identified, ordered by distance, and the nearest 12 (or fewer) are used for the spatial filtering. In this case the criteria corresponds for the vast majority of points to "using the 12 nearest points".

INSTALLATION
Source code spf_pt.c in ./IPTA/src, executable version spf_pt in ./IPTA/bin

DESCRIPTION
spf_pt supports the 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) and the maximum number of points considered, or just one of the two criteria by selecting all records in the other criteria.Together with the point list a point data stack of mask values can be indicated to consider or ignore specific points. "-" can be indicated instead a pmask file to consider all points of the list.

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.

For the spatial filtering constant weights or a linearly decreasing ramp (linear with ground distance) can be selected. Points with NULL values in the input data are not considered in the search for the nearest points (they are not counted as points in the filtering). For float data values, filtering based upon a least-squares planner fit to the data values is the default filtering method (spf_type = 2). This gives a better estimate of the filtered data when the data points are not uniformly distributed over the search region. This situation occurs at the edges of data.

In single point filtering mode where parameter pt_num is set, only the value of the data at point pt_num is altered, all other points in the input data stack are copied. The values of the mask array
are taken into account during the copy operation such that points with mask[i] = 0 are set to 0.

The average phase a single point can be viewed as a bias for the differential phase at for the image since by definition, the differential phase must be 0 at the reference point. Removal of this bias removes a noise contribution in the regression analysis.

OPTIONS
none.

SEE ALSO
ipta.h.