[FWTools] shift in contours lines gdal vs. grass gis
Chaitanya kumar CH
chaitanya.ch at gmail.com
Wed Aug 31 08:59:17 EST 2011
Can you compare the two contours with the pixel values? Which contours are
FYI, you can read the algorithm rules in the docs of GDALContourGenerate()
On Wed, Aug 31, 2011 at 6:42 PM, Rengifo Ortega <rengifoo at yahoo.de> wrote:
> Dear gdal users
> I hope you can help me with a question that is puzzling me, since a couple
> of days. So let me explain my problem.
> 2 years ago, I downloaded a SRTM 90m .asc file into GRASS GIS.
> A week ago, I decided to generate some contours lines using gdal_contour
> command (version FWTools2.4.7) and compare the contours lines with contours
> already produced in GRASS GIS. I was quite disturbed when in fact, I found a
> horizontal shift of the contours lines to the south of about -/+35m or to
> north (unknown distance), with respect to the grass gis- generated contours
> Technical aspect of my hardware
> I am in Grass GIS MS Windows environment (native using MinGW) combined
> with QGIS for visualisation purposes
> Using FWtools 2.4.7
> So, here are the steps I followed
> Part I
> -Produced 90m contours lines in GRASS GIS out of the SRTM DEM 90 by using
> the r.contour command
> -Visualised the contours lines in QGIS and saved them as shp format
> Part II
> 1) -Export SRTM 90 rasterfile as an ESRI ASCII GRID fomat and converted
> it to .tif format using FWTools2.4.7
> 2) Using gdal_contours utility I generated 90 meters contour lines
> Results 1
> Comparison between the GRASS-generated and the GDAL- generated contours
> lines exhibited a horizontal shift of -/+ 35m to the south in relation to
> GRASS GIS generated contours
> Part III
> 1--Export the raster file SRTM90m from GRASS GIS; as a Geotiff using gdal
> -Generate 90m contours using gdal
> Result 2
> Comparing the GRASS GIS contours with the geotiff- generated contours a
> displacement to the north was observed, no distance measured.
> I hope you can give some hints..
> best regards
> FWTools mailing list
> FWTools at lists.maptools.org
Chaitanya kumar CH.
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