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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] GSHAP data |
| Date: |
05/28/2007 11:28:40 AM |
| From: |
Quantitative Decisions |
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At 08:28 AM 5/28/2007 +0100, Keiko Saito wrote:
>GSHAP data (the global seismic
>hazard program)? I have downloaded the raw data with PGA values and the lat
>long of the grids, but when i try to import the data into arcinfo as an
>ASCII GRID file, the conversion process fails
The dataset available at http://www.seismo.ethz.ch/GSHAP/global/ is in the
format Longitude, Latitude, Value. It is tab-delimited with "NaN" used for
NoData values. The values are written row by row, top to bottom, in
increments of 0.1 degree.
This is not the same as the ESRI "ASCII GRID" format. It is readily
converted, though, by stripping the first two columns, changing "NaN" to a
constant numeric value, and prepending a header. The header should read
ncols 3601
nrows 1491
xllcorner -167
yllcorner -62
cellsize 0.1
nodata_value -9.9
(Use any number outside the range 0..10 for the NoData value.) The
resulting grid data set will occupy 23.32 MB on the disk (according to
ArcCatalog).
If you like, I can supply a command-line executable to do the conversion,
or you can write one yourself. The following source code, in AWK,
illustrates the procedure.
Cheers,
Bill Huber
Quantitative Decisions
#
# Convert GSHPUB.DAT to ESRI ASCII GRID export format.
#
BEGIN {
NoData = -9.9
XLLCorner = -167
XURCorner = 193
YLLCorner = -62
YURCorner = 87
CellSize = 0.1
NCols = (XURCorner - XLLCorner )/CellSize + 1
NRows = (YURCorner - YLLCorner )/CellSize + 1
print "ncols " NCols
print "nrows " NRows
print "xllcorner " XLLCorner
print "yllcorner " YLLCorner
print "cellsize " CellSize
printf("nodata_value %s", NoData)
}
$2 != Y {
print ""
Y = $2
}
{
if ($3 == "NaN")
Z = NoData
else
Z = $3
printf ("%s ", Z)
}
### end of file ###
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