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I'm new to QGIS.

I have GPS points uploaded to QGIS and a ⅓ arc-second DEM (USGS) of the area. I'd like to generate slope and aspect data for each point.

What is the best way to do this?

The point sampling tool only returns elevation data.

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Run the following QGIS Processing Algorithms against your DEM:

Slope
enter image description here Aspect
enter image description here

Once you have your newly generated Slope & Aspect rasters, run the Point Sampling tool against each to retrieve your values for Slope & Aspect.

If your points have Unique IDs, you can merge the tables into one aggregate table so that you end up with the points having all three attributes (elevation, slope, aspect) together.

As per a comment by CSK, you might be best able to merge these three products together taking the output of the first run of the point sampling tool (generating the points with elevation), and using them as the input layer for when you re-sample the Slope layer, then using that output as the input for when you re-sample the Aspect layer. This will result in all three attributes being in the final output, which you can then Make Permanent into an appropriate data storage (geopackage?).

enter image description here

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    Good answer. I have one improvement to suggest. Merge vector layers will give one layer with multiple copies of each point, and each point will only have one of the three values (elevation, slope, aspect). Instead, use the output from the first time you run the 'point sampling' tool as the input the second time you run the 'point sampling' tool, and the output from the second time as input for the third time. That way the final output will have all three values for every point, and no duplicate points. – csk Dec 9 '19 at 17:09
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    Yes, much better. I'll change my answer to reflect this. – Saijin_Naib Dec 9 '19 at 17:19
  • Awesome, thanks so much!! One follow-up question: I believe slope values are from 0 to 90°. My points cover a large variety of slopes, but all of the values start with 89.99xxx, which isn't correct. Would adjusting the Z-value correct this? The aspect values appear correct (I compared a number of them to a topo map). – Brian Allen Dec 9 '19 at 18:37
  • Potentially? Really hard to guess without seeing the data and how it is all set up. That might be a good follow-up question for you to ask if you gather some supporting information about the data and how you have it all set up. Maybe even links to it if you can share? – Saijin_Naib Dec 9 '19 at 18:52

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