Why doesn't my interpolation result in qgis look good?

Question

My goal is to use some RTK GPS data from combines or sprayers to generate an interpolated DEM of fields for agricultural purposes. I used QGIS for that. So far I opened the data and did a simple TIN interpolation with the interpolation tool in the raster drop-down. As input, I took the point layer and as the attribute the elevation. Somehow the result always looked like that:

Does anyone know why it doesn't work? I did the same steps as in the qgis tutorial about interpolating point data.

here is a part of the sample point attribute table:

Is the source point layer CRS defined as a projected or geographic coordinate system? — artwork21, Oct 30 '17 at 17:52
Would be great to post some rows of xyz values to check a sample data — aldo_tapia, Oct 30 '17 at 17:54
The source Layer is projected in WGS 84, which was the default. — M. Altenbach, Oct 30 '17 at 18:21
And what is also worth mentioning it, the IDW worked perfectly fine but doesn't really fulfil the purpose on elevation data — M. Altenbach, Oct 30 '17 at 18:23
Do you mean from the attribute table of the sample points? @aldo_tapia — M. Altenbach, Oct 30 '17 at 18:41
@aldo_tapia I got a screenshot of the attribute table in the post, does that help? — M. Altenbach, Oct 30 '17 at 18:49
In my opinion, I think that WGS 84 is not the proper CRS to work with for this case. Project to a CRS in the measurement unit (meter or feet). You have a densely populated data set with submillimeter z values from an herbicide application... I suspect that come from a tractor (I'm right?)... But, are enough accurate to this precision? I would clean some data before TIN creation, maybe is one solution. Also, did you try this approach? — aldo_tapia, Oct 30 '17 at 18:59
@aldo_tapia Yes, you are right, it is from a sprayer operation. I might try reprojecting the data first. I haven't tried the other approach yet, maybe this helps. I'll let you know. — M. Altenbach, Oct 30 '17 at 19:06
@M.Altenbach how does the QGIS heat map layer renderer look on the point layer? — DPSSpatial_BoycottingGISSE, Oct 30 '17 at 19:39
Can you open an issue on hub.qgis.org and share some data? I'd like to look into this. — ndawson, Oct 31 '17 at 02:48
I will give a try to v.surf.idw from the GRASS Processing Toolbox — Marco, Oct 31 '17 at 15:05
@DPSSpatial I tried the heatmap, but that didn't look very well. — M. Altenbach, Nov 01 '17 at 15:22
@ndawson I created an Issue on the qgis hub. It's issue #17374. Thanks for having a look. — M. Altenbach, Nov 01 '17 at 15:44
@Marco unfortunately that didn't work either, result is just a blank map — M. Altenbach, Nov 01 '17 at 15:44

score 1 · Answer 1 · answered Nov 01 '17 at 17:54

1

Alright, I finally got it. I always had projection issues, changing all the projections to UTM finally helped. Thanks for your help.

answered Nov 01 '17 at 17:54

M. Altenbach

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6

Why doesn't my interpolation result in qgis look good?

1 Answers1