Is there a way to create a relatively precise topographical map of a private land using GPS elevation data? As the land is a little bit over 100,000 square meters, the available regional topographical maps in Canada lack the precision I'd like to have for this project.

I have abundantly walked the land with a GPS and hence have thousands of points with elevation. Is there any way I could turn this into a somewhat interesting DEM or contour lines with QGIS?

  • Walking the area with a GPS might not give you the precision you want. A drone with images at regular intervals can easily serve as a basis for a DEM model made wit open source tools. – ragnvald May 11 '15 at 17:59
  • @ragnvald: This would work even if the land is heavily forested? – lpfavreau May 11 '15 at 18:06
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    With software and a camera you will get a point cloud of the surface. If this is woodland and you take your images in the autumn when the leaves have fallen chances are that you also will get points related to the ground. Even if you only can produce an elevation model based on your trees you could still deduct the height of the trees and get a ground level dem. The ultimate tool would of course be LIDAR. But that would be very expensive. Some authorities do such surveys anyway, so with some luck your area of interest has been mapped. – ragnvald May 11 '15 at 19:25
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    Hand held, consumer grade GPS unit? Elevations not likely to be all that accurate. Survey grade GPS unit? Might be viable data. While you're asking about QGIS (which core has fewer interpolation options, but more if you get into GRASS/PostGIS), this question is largely duplicate of gis.stackexchange.com/questions/103365 which was asked from the ArcGIS perspective. The general information is pretty much the same/applicable though. If you truly want an accurate/precise survey, you'll need to consider survey-grade GPS or a differential survey with a transit/rod. – Chris W May 11 '15 at 22:09
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    Can you do it, yes. The answer given largely covers it - the process is called interpolation, and there are different methods. Some of which are better suited to certain types of data than others. The rest of my earlier comment still stands and there is a lot of good/relevant info in the question I linked to and its answers. Accuracy of your GPS elevation readings and the distribution of your sample points are likely to be your biggest issues depending on what you actually want to do with the data/how accurate it needs to be. – Chris W May 12 '15 at 0:41

In QGIS you can use the Interpolation plugin (I think it is installed by default, if not it is a standard plugin installed through Plugin Manager) found in Raster -> Interpolation.

With that plugin you can take your vector layer of points and turn them into either a TIN or a surface model. You can either pull the elevation from a field in an attribute table or from the Z-Value if the points are true 3d points.

For a surface model select Inverse Distance Weighting and give the output file a .tif extension and you'll have a tif surface model that can be used to build contour lines, drainage models, etc.

The accuracy of the resulting data will depend on the accuracy of your GPS device, the number of points collected, and if they were collected accurately.

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  • If the area is heavily forested, make sure to take data when the leaves are off. Or try to get as many places with open sky view as you can get. – AndreJ May 12 '15 at 5:07

In the hope that new available datasets will be of help to others who are looking to achieve these results, here's my two cents:

To the question "Is there a way to create a relatively precise topographical map of a private land using GPS elevation data?", I fear the practical answer is no and will never change to yes especially if it's a heavily forested area. There is an alternative though.

Since I am pretty sure the OP is from Québec, it might be of interest to know that the government is in the process of rolling out lidar coverage for the southern parts of the province. You can check out if your area is already covered here:

overview of lidar campaigns and available tiles

If not, you'll have to wait a year or two or wait until 2022 or 2023 when the last campaigns will conclude.

These datasets are very precise, at a spatial resolution of 1m (each pixel has 1m sides) and the vertical accuracy is under 30cm. You can build contour lines at 1m interval with confidence.

This of course also applies to any other area with similar coverage, making consumer grade GPS survey pretty much useless.

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  • Thanks! Very useful! Rollout for my area seems to be around 2019. I'll keep an eye on it. – lpfavreau Jun 13 '18 at 12:57

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