NAME¶
blockmean - filter to block average (x,y,z) data by L2 norm
SYNOPSIS¶
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] ]
DESCRIPTION¶
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.
OPTIONS¶
- -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].
EXAMPLES¶
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
SEE ALSO¶
blockmedian(1gmt),
blockmode(1gmt),
gmtdefaults(1gmt),
gmt(1gmt),
nearneighbor(1gmt),
surface(1gmt),
triangulate(1gmt)