2

I have a manual QGIS system that starts when I load a GPX file into QGIS and perform a number of actions on it. It all works perfectly.

I want to automate this process using the QGIS Graphical Modeler, so I can batch process a whole directory of GPX files.

When I start the process manually the GPX import dialogue box asks which vector layers I want to load from the GPX file:enter image description here

I select the tracks layer and everything proceeds smoothly.

To automate my system I use the Vector Layer Input element in the Graphical Modeler. I define the import as Line so that it can be picked up by Polygonize.

enter image description here

However, when I try to polygonize this line layer the process fails - I am not sure why - maybe because there are no routes defined in my GPX files?

UPDATE: I swapped the <trk> and <trkpt> tags for <rte> and <rtept> tage in a GPX file and made a 'route layer'. Manually I was able to make a polygon from the route line but, once again, the automated model failed failed to make a polygon.

Is there a way to get around this problem? I have tried many different things including GPS Tools, Batch GPS Importer, Merging layers, Fixing geometries. I have run out of ideas.

As requested by Erik:

Here is an example track: enter image description here

I can polygonize the "loop" manually - but not with the Graphical Modeler: enter image description here

The Graphical Model: enter image description here

Sample GPX (of a shorter track) made with the same GPX tracker:

    <?xml version="1.0" encoding="UTF-8"?>
<gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.topografix.com/GPX/1/1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd" version="1.1" creator="Open GPX Tracker for iOS">
    <trk>
        <trkseg>
            <trkpt lat="50.92371170879427" lon="0.7082069478935639">
                <ele>1.6512947082519531</ele>
                <time>2020-05-16T15:12:17Z</time>
            </trkpt>
            <trkpt lat="50.923746284144855" lon="0.7085257116711777">
                <ele>17.26394271850586</ele>
                <time>2020-05-16T15:12:18Z</time>
            </trkpt>
            <trkpt lat="50.9237622516704" lon="0.7084496039903802">
                <ele>36.04580307006836</ele>
                <time>2020-05-16T15:12:20Z</time>
            </trkpt>
            <trkpt lat="50.92375919227574" lon="0.7084884960210961">
                <ele>35.53786849975586</ele>
                <time>2020-05-16T15:12:22Z</time>
            </trkpt>
            <trkpt lat="50.923756803433335" lon="0.7085274718708438">
                <ele>33.56557846069336</ele>
                <time>2020-05-16T15:12:23Z</time>
            </trkpt>
            <trkpt lat="50.92375382785771" lon="0.7085764221853657">
                <ele>33.50826644897461</ele>
                <time>2020-05-16T15:12:24Z</time>
            </trkpt>
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                <ele>33.09322738647461</ele>
                <time>2020-05-16T15:12:25Z</time>
            </trkpt>
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                <ele>33.21499252319336</ele>
                <time>2020-05-16T15:12:26Z</time>
            </trkpt>
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                <ele>33.34707260131836</ele>
                <time>2020-05-16T15:12:27Z</time>
            </trkpt>
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                <ele>32.77730941772461</ele>
                <time>2020-05-16T15:12:28Z</time>
            </trkpt>
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                <ele>33.23983383178711</ele>
                <time>2020-05-16T15:12:29Z</time>
            </trkpt>
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                <ele>33.10921859741211</ele>
                <time>2020-05-16T15:12:30Z</time>
            </trkpt>
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                <ele>32.85805892944336</ele>
                <time>2020-05-16T15:12:31Z</time>
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                <ele>32.01839828491211</ele>
                <time>2020-05-16T15:12:32Z</time>
            </trkpt>
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                <time>2020-05-16T15:12:33Z</time>
            </trkpt>
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                <ele>30.08053207397461</ele>
                <time>2020-05-16T15:12:34Z</time>
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                <time>2020-05-16T15:12:35Z</time>
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                <time>2020-05-16T15:12:37Z</time>
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                <time>2020-05-16T15:12:38Z</time>
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                <time>2020-05-16T15:12:39Z</time>
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                <time>2020-05-16T15:12:51Z</time>
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                <time>2020-05-16T15:12:52Z</time>
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                <time>2020-05-16T15:12:54Z</time>
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                <time>2020-05-16T15:12:55Z</time>
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</gpx>

Data Log: With QGIS Graphical Modeler:

Prepare algorithm: qgis:polygonize_1
Running Polygonize [1/6]
Input Parameters:
{ INPUT: '/Users/peqi/Downloads/GPX/16-May-2020-1531.gpx', KEEP_FIELDS: False, OUTPUT: 'memory:Polygons from lines' }
Processing lines…
Noding lines…
Polygonizing…
No polygons were created!
OK. Execution took 0.165 s (1 outputs).

Manually:

Processing algorithm…
Algorithm 'Polygonize' starting…
Input parameters:
{ 'INPUT' : '/Users/peqi/Downloads/GPX/16-May-2020-1531.gpx|layername=tracks', 'KEEP_FIELDS' : False, 'OUTPUT' : 'TEMPORARY_OUTPUT' }

Processing lines…
Noding lines…
Polygonizing…
Saving polygons…
Execution completed in 0.10 seconds
Results:
{'OUTPUT': 'Polygons_from_lines_44578c71_16a0_40b5_827e_a6ce3393bfe5'}

Loading resulting layers
Algorithm 'Polygonize' finished

Model script: https://pastebin.com/m8uSnARj

Compare manual input:

'INPUT' : '/Users/peqi/Downloads/GPX/16-May-2020-1531.gpx|layername=tracks'

with the Model:

{ INPUT: '/Users/peqi/Downloads/GPX/16-May-2020-1615.gpx', KEEP_FIELDS: False, OUTPUT: 'memory:Polygons from lines' }

Is that missing '... |layername=tracks' the problem?

Improve this question
10
  • You are wondering why you can't create polygons from non-closed lines? Why are you trying to polygonize in the first place? What result do you expect? Commented Aug 13, 2020 at 12:08
  • They are closed lines. Commented Aug 13, 2020 at 12:14
  • The manual process works fine. I can't work out how to automate it with the Graphical Modeler. Commented Aug 13, 2020 at 12:15
  • Can you share example data and the model? Commented Aug 13, 2020 at 12:17
  • Here you are. Thanks for helping. Commented Aug 13, 2020 at 13:04

1 Answer 1

Reset to default
0

The GPX file needs to be converted into a .shp file before it can be processed by the Graphical Modeler.

Load the .gpx file as a layer in QGIS, right click on the layer in the layer browser >> export >> save as >> ESRI Shapefile (give it a name and select a writable destination directory).

This cannot be done as a QGIS batch process (as far as I know)

This .shp file can be opened and processed by the graphical modeler.

Improve this answer
6
  • No - it's the start of a whole new heap of (unnecessary) pain. Commented Aug 13, 2020 at 20:58
  • Isn't the answer enough? Commented Aug 13, 2020 at 21:23
  • It is a complete answer. Commented Aug 13, 2020 at 21:29
  • .shx is the offset information for a shapefile. No file geodata format could be converted into the fixed width feature offset file, so this makes no sense as a comment, much less as an answer. Commented Aug 13, 2020 at 21:30
  • With QGIS (open .gpx >> export as .shx) - but not with the Graphical Modeler. Commented Aug 13, 2020 at 21:33

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