[Gdal-dev] [GDAL_Contours]Different gridcellsizes
Paul Meems
meems at soilcompany.nl
Thu Mar 2 02:02:40 EST 2006
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<DIV><SPAN class=590033607-01032006><FONT face=Arial><FONT size=2><SPAN
class=402375906-02032006><FONT
color=#000000>H</FONT></SPAN>i,</FONT></FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>This is my first
post to this list.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>I'm a member of the
MapWindow Developing Team (<A
href="http://www.mapwindow.org">www.mapwindow.org</A>) and MapWindow (MW) is
using GDAL.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>One of the used
functions of GDAL is the 'Generate Contours from Grid'.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>Regarding this
function I have some questions.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>I want to use it to
convert Surfer 7 gridfiles (<A
href="http://www.goldensoftware.com">www.goldensoftware.com</A>) to shapefiles.
Using the current GDAL_Contour function it is allmost working. A shapefile
is produced but because Surfer uses different gridcellsizes for X and Y the
created contours are shifted.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>So my question is
can GDAL_Contour be altered so it can handle different
gridcellsizes?</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>The difference
between a 'normal' gridfile and a gridfile with different gridcellsizes is in
the header:</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>A normal
gridfile:</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2>NCOLS 96<BR>NROWS 83<BR>XLLCENTER 200022.735<BR>YLLCENTER 598252.6382<BR>CELLSIZE
3.49626421052656<BR>NODATA_VALUE -99</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>A different
gridcellsizes gridfile:</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2>NCOLS 96<BR>NROWS 83<BR>XLLCENTER 200022.735<BR>YLLCENTER 598252.6382<BR>DX 3.49626421052656<BR>DY 3.50804024390172<BR>NODATA_VALUE -99</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>Notice the DX and DY
lines comparing with the CELLSIZE line in the equal one.<BR>The new gridobject
in MW is handling this correctly.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial color=#0000ff size=2><SPAN
class=402375906-02032006>I've made a zipfile with some sample data.
It's available at <A
href="http://bugs.mapwindow.org/show_bug.cgi?id=88">http://bugs.mapwindow.org/show_bug.cgi?id=88</A> </SPAN></FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>The zipfile
containes a ppt-file with the gridfile overlaid with the correct contoured
shapefile by my own function (this file, Correct_contour.shp is included as
well) and with a shapefile (grid_with_different_gridsizes_Contour.shp, included
as well) created by the<BR>Contour-function of MW (using the GDAL_Contour), this
one is in red and is shifted.<BR>I also include two gridfiles who have the
same data only different headers.<BR>One is with equal gridcellsizes
(grid_with_equal_gridsizes.asc) and the other is with different gridcellsizes
(grid_with_different_gridsizes.asc).</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>I'm just a VB6
programmer so I hope someone of the GDAL Developing Team would look into
it.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>When GDAL handles
the different gridcellsizes correctly MapWindow will as
well.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>And I would be very
happy because the GDAL_Contour is much faster than my own VB6 function
;)</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>Thanks in
advanced.</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>Paul
Meems</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial size=2>The
Netherlands</FONT></SPAN></DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=590033607-01032006><FONT face=Arial
size=2></FONT></SPAN> </DIV></BODY></HTML>
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