Re: Geosoft Grid to netCDF???

From: Dan Scheirer <dssmailing@...>
Subject: Re: [GMT-HELP] Geosoft Grid to netCDF???
To: GMT-HELP@...
Date: Tuesday, 28 October, 2008, 4:53 AM

Santosh,

I don't believe that there is a direct way to do this conversion.  

One way in which I have done this conversion is to use Geosoft's
Oasis Montaj free viewer to open the binary, native-Geosoft
grid format and then to save it in Geosoft's ASCII, open grid-exchange
format (GXF).  This software is available for Windows at:
   http://www.geosoft.com/pinfo/oasismontaj/free/montajviewer.asp

Then, I tried to use gdal_translate, from the GDAL package, to convert
the GXF format to GMT's netcdf format.  A description of GDAL's
support for GXF can be found at:
   http://home.gdal.org/projects/gxf/index.html

I said "tried to use" gdal_translate because GDAL's
implementation
of a year or so ago (and I presume now, also) didn't allow proper
opening of grids in some grid-array-orientations (e.g. which corner of
the grid does the first cell occupy? does the grid loop through rows
or
 columns first?).

Thus, I just took the GXF file and with some simple
head/tail/awk/dos2unix's 
to extract the header-information and the array of grid-values, I was
able to devise an xyz2grd -Z...
command that created a suitable grid.  The GXF file's header will
contain the same information as you have below in the "Raster
Information"; it will also contain information about the location
of the first grid-cell and the grid-array-orientation.

GDAL might work in your case and might be simplest; the xyz2grd
solution would be quick, too, if you have done this kind of command-line
construction before.  In either case, you'd need to convert to GXF
using the free Geosoft tool, because I'm pretty sure that the
binary, native Geosoft grid format is not documented.

Good luck,
Dan Scheirer


----- Original Message ----
> From: Santosh Panda <santoshh19@...>
> To:
 GMT-HELP@...
> Sent: Monday, October 27, 2008 3:58:29 PM
> Subject: [GMT-HELP] Geosoft Grid to netCDF???
> 
> Hi All,
> 
> I have a raster image in Geosoft Grid format. It is generated in Oasis
> Montaj Geosoft software, and pixel values are apparent resistivity in
Ohm.m.

> 
> How can I open it in GMT or export it to netCDF format? I would highly
> appreciate any suggestions.
> 
> Raster image details is as follows:
> 
> Raster Information:
> Columns & Rows : 9792X7837
> Band                    : 1
> Cell size               : 25X25
> Uncompressed size: 292.74 MB
> Format                : Geosoft Grid
> Source Type        : continuous
> Pixel Type           : floating point
> Pixel Depth         : 32 Bit
> No Data Value    : -1e+032
> Pyramid              : Present
> Compression       :
 None
> Status                 : Permanent
> 
> Spatial Reference: NAD_1927_UTM_Zone_7N
> Linear Unit : Meter (1.000000)
> Angular Unit: Degree (0.017..........)
> False Easting: 500000
> False Northing: 0
> Central Meridian: -141
> Scale Factor: 0.9996
> Latitude_Of_Origin: 0
> Datum : D_North_American_1927
> 
> Thanks,
> Santosh
> 
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