[Qgis-user] DEM error with OpenDataNRW

Mon Nov 16 11:09:10 PST 2020

Thanks a lot for your help!
It seems that correct functionality only depends on the sequence and sorting of Y and X !?
"Cells with same Y coordinates must be placed on consecutive lines. For a same Y coordinate value, the lines in the dataset must be organized by increasing X values"

The data that works (http://www.vermkv.service24.rlp.de/opendat/dgm25/dgm25.zip) is sorted according to these organizing rules with ascending X for same Y...:

400000.000 5470000.000 347.382
400025.000 5470000.000 345.370
400050.000 5470000.000 342.344
400075.000 5470000.000 341.794
400100.000 5470000.000 340.223
400125.000 5470000.000 337.833

The NRW data sort the other way round (see below). So I probably "just" will have to rearrange Y and X in the NRW data to get it ready ... ... ... Yes, works! Cool.

Thanks again!
Martin

Von: Nicolas Cadieux <njacadieux.gitlab at gmail.com>
Gesendet: Montag, 16. November 2020 18:54
An: Prof. Dr. Martin Berchtold <martin.berchtold at ru.uni-kl.de>; qgis-user at lists.osgeo.org
Betreff: Re: [Qgis-user] DEM error with OpenDataNRW

Hi,

I believe, but Even will confirm, that the data is not organized correctly for the gdal driver. I looked at line 2001 and the file is organized by x value with incrementing y values.  The x value is constant and the y value change on every line.  The error is detected on line 2001 when the x value changes
x y z
32342000.00 5659997.00   43.35
32342000.00 5659998.00   43.41
32342000.00 5659999.00   43.34
32342001.00 5658000.00   45.16 (line 2001)
32342001.00 5658001.00   45.13
32342001.00 5658002.00   45.00

I reprojected and srtm and save it as a xyz using gdal12xyz and this is what I got for the first few lines

xyz

26548864.985 8824521.429 -32768
26548904.304 8824521.429 -32768
26548943.623 8824521.429 -32768
26548982.941 8824521.429 -32768
and at line 4749 thing change to a new y coordinate
26735471.145 8824521.429 -32768
26735510.464 8824521.429 -32768
26548864.985 8824482.110 -32768
26548904.304 8824482.110 -32768

As you can see, the x values changes on every line and the y value is constant as stated in https://gdal.org/drivers/raster/xyz.html
"The spacing between each cell must be constant and no missing value is supported. Cells with same Y coordinates must be placed on consecutive lines. For a same Y coordinate value, the lines in the dataset must be organized by increasing X values. The value of the Y coordinate can increase or decrease however. The supported column separators are space, comma, semicolon and tabulations."

I am not sure the driver can handle this.  You can however open the data as a csv and rasterize or interpolate the data (using nearest neighbor) If you use the same pixel size and posting, this will work and not change the data.

Perhaps Even R. has a solution.
Nicolas

On 2020-11-16 9:49 a.m., Prof. Dr. Martin Berchtold wrote:
Dear all,

could somebody please explain me why QGIS doesn't process the DEM1 data from OpenDataNRW (.xyz, 1 meter, Nordrhein-Westfalen) while the DEM25 data from OpenDataRLP (.xyz, 25m, Rheinland-Pfalz, but congruent structure to NRW) works out without any problem???

Error message:
UngÃ¼ltiger Layer: GDAL provider Cannot open GDAL dataset C:/[...]/dgm1_05315000_KÃ¶ln_EPSG4647_XYZ/dgm1_32342_5658_2_nw.xyz: Ungridded dataset: At line 2001, change of Y direction Raster layer Datenanbieter ist ungÃ¼ltig (Anbieter gdal, URI: C:/[...]/dgm1_05315000_KÃ¶ln_EPSG4647_XYZ/dgm1_32342_5658_2_nw.xyz

There is no change at line 2001... I have no idea, esp. because I can process the NRW files in ArcGIS pro without any problem.

Is there a limit of file size or line numbers?

Thanks for any help und kind regards
Martin

---

dvmP
Digitalisierung, Visualisierung & Monitoring in der Raumplanung
Jun.-Prof. Dr. Martin Berchtold

TU Kaiserslautern, Fachbereich Raum- und Umweltplanung
PfaffenbergstraÃŸe 95 | D 67663 Kaiserslautern
Geb. 1, R. U28
T +49 631 205-5151 | M +49 177 3692249
martin.berchtold at ru.uni-kl.de<mailto:martin.berchtold at ru.uni-kl.de>
www.ru.uni-kl.de/dvmP<http://www.ru.uni-kl.de/dvmP>

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