[Qgis-user] Fw: Aw: Create contours algorithm does not work

Sun Oct 8 22:41:17 PDT 2023

Hi list,
using
GDAL > Raster projections > Assign projection
did the trick.
Now I get beautiful contour lines as expected (directly in QGIS).

Thanks you Alister for pointing this out!

Regards,
Rolnad

    Date: Wed, 4 Oct 2023 16:44:38 +0200
    From: Roland Spielhofer <rspiel at gmx.net>
    To: QGIS User <qgis-user at lists.osgeo.org>
    Subject: [Qgis-user] Create contours algorithm does not work
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            <trinity-9299223f-260f-4956-9a59-0adffff051d1-1696430678309 at 3c-app-gmx-bs35>

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Hi Roland,

I note that your gdalinfo output does not include the usual "Coordinate System is:" section after the "Size" line.
You will probably find it works as expected if you rectify this, by specifying a projection using the "assign projection" or "translate (convert format)" QGIS processing tools.

I tend to have the same problem when working with "Arc/Info ASCII Grid" files produced by 12D - in this case gdalinfo prints a "Coordinate System is:" section but it just looks like this, instead of actually having the coordinate system details:

Coordinate System is `'

I simply use "translate (convert format)" to convert to a geotiff and specify the correct coordinate system, and I have no problem generating contours from that geotiff.

PS I was only able to read your email after clicking the link for the "scrubbed" html attachment, and ignoring all the html code - see above.  If you want everybody on the list to actually read your emails you should configure your email client to also send plain text email instead of just sending html email.

Regards,
Alister

Gesendet: Donnerstag, 05. Oktober 2023 um 12:23 Uhr
Von: "Roland Spielhofer" <rspiel at gmx.net>
An: "QGIS User" <qgis-user at lists.osgeo.org>
Betreff: Aw: [Qgis-user] Create contours algorithm does not work

Just wanted to add that I also tried the latest gdal_contour CLI command - with the same result.

gdalinfo of the raster-tif says:

Driver: GTiff/GeoTIFF
Files: Axx_PPS_1_0000_Z.tif
Size is 1291, 3701
Origin = (590694.146499999915250,5311061.004799999296665)
Pixel Size = (0.050000000000000,-0.050000000000000)
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (  590694.146, 5311061.005)
Lower Left  (  590694.146, 5310875.955)
Upper Right (  590758.696, 5311061.005)
Lower Right (  590758.696, 5310875.955)
Center      (  590726.421, 5310968.480)
Band 1 Block=1291x1 Type=Float32, ColorInterp=Gray
  Min=312.351 Max=314.506
  Minimum=312.351, Maximum=314.506, Mean=313.375, StdDev=0.602
  NoData Value=-99999
  Metadata:
    STATISTICS_MAXIMUM=314.50564575195
    STATISTICS_MEAN=313.37469987748
    STATISTICS_MINIMUM=312.35101318359
    STATISTICS_STDDEV=0.60238892993285

Anything wrong with it?

It has been generated by SAGA by rastering a pointcloud.

Regards,
Roland

Gesendet: Mittwoch, 04. Oktober 2023 um 16:44 Uhr
Von: "Roland Spielhofer via QGIS-User" <qgis-user at lists.osgeo.org>
An: "QGIS User" <qgis-user at lists.osgeo.org>
Betreff: [Qgis-user] Create contours algorithm does not work

Hi,
I have a 1-band raster representing the surface of a road - the pixels hold the z-values/elevation.
I have loaded it into QGIS and used "contours" as renedering method. The result looks good, I additionally have the same raster with hillshading as rendering - very pleasent - see
https://imgur.com/XMmMmdj
the fuzzy black lines are the contours, the light area is the hillshaded z-raster.

One drawback of the on-the-fly contours is that they are limited to a minimum interval of 0.1 m. As the surface is very flat (a road), I would like to have a more dense set of contours (0.02 m, e.g.).

I tried the contours function (GDAL > Raster extraction > contours) from the processing toolbox. It created a new layer with a plausible number of lines, but the lines are not visible, no matter what I try. The log of Contour is below - I do not see anything special.
I tried to calculate the length of the geometries, but I get "nan" for each.

Any ideas why the contours function does not produce meaningful output while the rendering as contours works beautifully?

Kind regards,
Roland

QGIS version: 3.32.1-Lima
QGIS code revision: 4a078ecf63
Qt version: 5.15.3
Python version: 3.9.5
GDAL version: 3.7.1
GEOS version: 3.12.0-CAPI-1.18.0
PROJ version: Rel. 9.2.1, June 1st, 2023
PDAL version: 2.5.5 (git-version: a7569c)
Algorithm started at: 2023-10-04T16:39:30
Algorithm 'Contour' starting…
Input parameters:
{ 'BAND' : 1, 'CREATE_3D' : False, 'EXTRA' : '', 'FIELD_NAME' : 'ELEV', 'IGNORE_NODATA' : False, 'INPUT' : 'Q:/RoadSTAR/Archiv/_Diverses ohne Proj.Nr/A02_Detailauswertung/A02_2-1_km28,080_km27,694___230713_1758/A02_2-1_KM28,147_KM27,957_230713_1758/GeoTIFF/A02_2-1_KM28,147_KM27,957_230713_1758_PPS_1_0000_Z.tif', 'INTERVAL' : 0.1, 'NODATA' : None, 'OFFSET' : 0, 'OUTPUT' : 'TEMPORARY_OUTPUT' }

GDAL command:
gdal_contour -b 1 -a ELEV -i 0.1 -f "GPKG" "Q:\\RoadSTAR\\Archiv\\_Diverses ohne Proj.Nr\\A02_Detailauswertung\\A02_2-1_km28,080_km27,694___230713_1758\\A02_2-1_KM28,147_KM27,957_230713_1758\\GeoTIFF\\A02_2-1_KM28,147_KM27,957_230713_1758_PPS_1_0000_Z.tif" C:/Users/lokaladmin/AppData/Local/Temp/processing_lqTuzZ/d902fb853ce246a59f2768d2f0607ba6/OUTPUT.gpkg
GDAL command output:
0...10...20...30...40...50...60...70...80...90...100 - done.
Process completed successfully
Execution completed in 0.39 seconds
Results:
{'OUTPUT': 'C:/Users/lokaladmin/AppData/Local/Temp/processing_lqTuzZ/d902fb853ce246a59f2768d2f0607ba6/OUTPUT.gpkg'}

Loading resulting layers
Algorithm 'Contour' finished

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