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<p class=MsoNormal><span style='color:#1F497D'>Man this is the bane of my
existence. I too was challenged with the requirement to extract data in Mapinfo
from a Vertical Mapper grid.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Vertical Mapper grids are
actually not native grids to Mapinfo. Vertical mapper was written by a third
party called Northwood Geosceince in Canada. Mapinfo acquired them some years
ago as I understand it.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Other then the VMSDK which is
about USD$700 there is almost nothing about the format available.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>If it’s not against the
rules of the forum here is a link to the Mapinfo-L Google Group with athread I
started about this very issue.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>http://groups.google.com/group/mapinfo-l/browse_thread/thread/175f375be41d7e23<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I also had a colleague who did
some work on breaking down the format.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Below are his discoveries. His skills
far exceed mine.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I hope you can make use of this.<o:p></o:p></span></p>
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<p class=MsoNormal style='border:none;padding:0cm'><span style='color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><span style='font-size:10.0pt'>byte 0, 4 characters
"HGPC"</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 4, 1 character
"1" (version)</span><o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 9, 2 byte integer - no
of X pixels</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 11, 2 byte integer - no
of Y pixels</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 13, 8 byte double - min
X coordinate </span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 21, 8 byte double - max
X coordinate</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 29, 8 byte double - min
Y coordinate</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 37, 8 byte double - max
Y coordinate</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 45, 4 byte float - min Z
value</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>byte 49, 4 byte float - max Z
value</span><o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>Data starts at byte 1028 and
is a stream of 16-bit integer</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>values. 0 is
noval. Data is stretched to use values</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>1-65535. Use Z min and
Z max to reconstruct original</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>Z values.</span><o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal> <span style='font-size:10.0pt'>Some resources I've
found:</span><o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>This includes a file spec for
a related file format - not the same but documents some conventions</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'><a
href="http://testdrive.mapinfo.com/TECHSUPP/MIPROD.NSF/0/9ba1b248cfac072285256eae004d123e/$FILE/SDK%202.6.pdf">http://testdrive.mapinfo.com/TECHSUPP/MIPROD.NSF/0/9ba1b248cfac072285256eae004d123e/$FILE/SDK%202.6.pdf</a></span><o:p></o:p></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'>Some basic code for the 3d
file format</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt'><a
href="http://testdrive.mapinfo.com/techsupp/miprod.nsf/kbase_by_product/BAABD8094414825785256D12004CD1CE">http://testdrive.mapinfo.com/techsupp/miprod.nsf/kbase_by_product/BAABD8094414825785256D12004CD1CE</a></span><o:p></o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><b><u><span style='font-size:16.0pt;color:#1F497D'>AND<o:p></o:p></span></u></b></p>
<p class=MsoNormal>I managed to get the first GRD file loaded into PostGIS<br>
with my python code.<br>
<br>
To match the alignment with our reference data I had to add an offset of<br>
exactly 2 grid pixels east, which is a bit odd, but there you<br>
go. I expected a half-pixel uncertainty since I wasn't sure if the<br>
coordinates are the centre or edge of the pixel, but a 2 pixel<br>
shift doesn't make any obvious sense.<br>
<br>
I'd suggest if you are uncertain about your file types the<br>
Vertical Mapper GRD files are easily distinguished by the<br>
characters "HGPC " in the first 4 bytes. If the 5th byte<br>
is "." then it is a 3d file, which is well documented. If the<br>
5th byte is "1" then it is a 2d file, which is what I have, and<br>
I have not found documentation.<br>
<br>
I used a Unix box (FreeBSD) for my exploratory analysis. If you have<br>
access to one you can check the first bytes for this signature<br>
with something like this:<br>
od -c myfile.grd | head<br>
<br>
<span style='color:#1F497D'><o:p></o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
gdal-dev-bounces@lists.osgeo.org [mailto:gdal-dev-bounces@lists.osgeo.org] <b>On
Behalf Of </b>Ned Harding<br>
<b>Sent:</b> Saturday, 14 June 2008 1:30 AM<br>
<b>To:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> [gdal-dev] Vertical Mapper GRD files<o:p></o:p></span></p>
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</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Does anyone have any information about how to read Vertical
Mapper GRD/GRC files? I haven't been able to find much on them.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Ned Harding<o:p></o:p></p>
<p class=MsoNormal>CTO<o:p></o:p></p>
<p class=MsoNormal>SRC, LLC<o:p></o:p></p>
<p class=MsoNormal>3825 Iris Avenue, Suite 150<o:p></o:p></p>
<p class=MsoNormal>Boulder, CO 80301<br>
(303) 440-8896 x104<br>
<a href="mailto:nharding@extendthereach.com">nharding@extendthereach.com</a><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Visit SRC on the web at <a
href="http://www.extendthereach.com/">www.ExtendTheReach.com</a><o:p></o:p></p>
<p class=MsoNormal>See SRC in Action at <span style='color:blue'><a
href="http://www.demographicsnow.com/">www.DemographicsNow.com</a></span><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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