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Trying to generate isodistances/isochrones in the QNEAT 3 plugin I got the following error:

> Traceback (most recent call last): File
> "C:/Users/User/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\QNEAT3\algs\IsoAreaAsPolygonsFromPoint.py",
> line 249, in processAlgorithm polygon_featurelist =
> net.calcIsoPolygons(max_dist, interval, output_path) File
> "C:/Users/User/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\QNEAT3\Qneat3Framework.py",
> line 469, in calcIsoPolygons band_in = ds_in.GetRasterBand(1)
> AttributeError: 'NoneType' object has no attribute 'GetRasterBand'
> Execution failed after 53.74 seconds

Parameters:

parameters

All layers are in a projected CRS. Matplotlib library in the OSGeo4W Shell has been installed.

I am using QGIS 3.6.1

I have tried to play a bit with different parameters but without success (seems it doesn´t have any influence on the error message). Besides I still don´t understand the meaning of the contour interval parameter...?

QNEAT3 infopage

Related thread (but unfortunately didn´t answer my question).

Creating isochrones in QGIS using QNEAT3

Any thoughts why I´m getting this error?

UPDATE: Changing the parameters so the contour interval >> raster size:

parameters_02

After reprojecting the network layer to a projected CRS via the appropriate geoprocessing tool:

isochrones

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  • Did my answer below help? Or do you still run into errors?
    – root676
    Oct 13, 2019 at 9:05
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    Via the contour interval you can set the number of isochrones/isodistances. So when the size of the Iso-Area is 2,500 m and the contour interval is 500 m, 5 polygons will be generated. The raster size should be therefore always lower then the contour interval (now it makes sense) to find the appropriate pattern. To answer your second question: No, I still get the same "GetRasterband" error.
    – Mapos
    Oct 13, 2019 at 9:35
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    CRS: EPSG:5243 - ETRS89 / LCC Germany (E-N) - Projected (layer + project); default speed: 5km/h. To speed up the calculations I have created a subset of roads layer (clip by polygon, radius ca. 5 km). Layer is from GEOFABRIK.
    – Mapos
    Oct 13, 2019 at 9:44

1 Answer 1

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You should once again think about the parameters you chose. QNEAT3 uses an interpolation raster for creating the isochrones on a network. You chose a cell size of 1000x1000m and entered a contour interval of 1m. How should the contour algorithm find a contour in a single 1x1km raster cell? Switch the parameters to a 1x1m cell size and a suitably large contour interval level. Then you won't get the error about a missing raster layer.

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    Well the problem was associated with the wrong CRS. The Geofabrik layers have WGS84 as CRS. To set the CRS in the project doesn´t suffice. The layers have to be reprojected in a projected CRS (via the appropriate tool). Then the raster error dissappears cause the calculations now base on the actual projected CRS. Neverthless many thanks for your help.
    – Mapos
    Oct 13, 2019 at 14:08

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