blockmean - filter to block average (x,y,z) data by L2 norm
blockmean [
xyz[w]file(s) ]
-Ix_inc[
m|c][/
y_inc[
m|c]]
-Rwest/east/south/north[
r] [
-C ] [
-F ] [
-H[
nrec] ] [
-L ] [
-S ] [
-V ] [
-W[
io] ] [
-: ] [
-bi[
s][
n] ] [
-bo[
s][
n] ]
blockmean reads arbitrarily located (x,y,z) triples [or optionally
weighted quadruples (x,y,z,w)] from standard input [or
xyz[w]file(s)]
and writes to standard output a mean position and value for every non-empty
block in a grid region defined by the
-R and
-I arguments.
Either
blockmean,
blockmedian, or
blockmode should be
used as a pre-processor before running
surface to avoid aliasing short
wavelengths. These routines are also generally useful for decimating or
averaging (x,y,z) data. You can modify the precision of the output format by
editing the D_FORMAT parameter in your .gmtdefaults file, or you may choose
binary input and/or output using single or double precision storage.
- xyz[w]file(s)
- 3 [or 4] column ASCII file(s) [or binary, see -b]
holding (x,y,z[,w]) data values. [w] is an optional weight for the data.
If no file is specified, blockmean will read from standard
input.
- -I
-
x_inc [and optionally y_inc] is the grid
spacing. Append m to indicate minutes or c to indicate
seconds.
- -R
-
west, east, south, and north specify the
Region of interest. To specify boundaries in degrees and minutes [and
seconds], use the dd:mm[:ss] format. Append r if lower left and
upper right map coordinates are given instead of wesn.
- -C
- Use the center of the block as the output location [Default
uses the mean location].
- -F
- Block centers have pixel registration. [Default: grid
registration.] (Registrations are defined in GMT Cookbook Appendix B on
grid file formats.) Each block is the locus of points nearest the grid
value location. For example, with -R10/15/10/15 and and -I1:
with the -F option 10 <= (x,y) < 11 is one of 25 blocks;
without it 9.5 <= (x,y) < 10.5 is one of 36 blocks.
- -H
- Input file(s) has Header record(s). Number of header
records can be changed by editing your .gmtdefaults file. If used,
GMT default is 1 header record. Not used with binary data.
- -L
- Indicates that the x column contains longitudes, which may
differ from the region in -R by [multiples of] 360 degrees [Default
assumes no periodicity].
- -S
- Report the sum of all z-values inside a block [Default
reports mean value].
- -V
- Selects verbose mode, which will send progress reports to
stderr [Default runs "silently"].
- -W
- Weighted modifier[s]. Unweighted input and output has 3
columns x,y,z; Weighted i/o has 4 columns x,y,z,w. Weights can be used in
input to construct weighted mean values in blocks. Weight sums can be
reported in output for later combining several runs, etc. Use -W
for weighted i/o, -Wi for weighted input only, -Wo for
weighted output only. [Default uses unweighted i/o]
- -:
- Toggles between (longitude,latitude) and
(latitude,longitude) input/output. [Default is (longitude,latitude)].
Applies to geographic coordinates only.
- -bi
- Selects binary input. Append s for single precision
[Default is double]. Append n for the number of columns in the
binary file(s). [Default is 3 (or 4 if -W is set)].
- -bo
- Selects binary output. Append s for single precision
[Default is double].
To find 5 by 5 minute block means from the ASCII data in hawaii.xyg, try
blockmean hawaii.xyg
-R198/208/18/25
-I5
m >
hawaii_5x5.xyg
blockmedian(1gmt),
blockmode(1gmt),
gmtdefaults(1gmt),
gmt(1gmt),
nearneighbor(1gmt),
surface(1gmt),
triangulate(1gmt)