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Post by statto on Jan 20, 2023 7:16:01 GMT -5
...you can convert an elevation profile TO LIDAR.
I'm not going to do a great job explaining this at the moment but here we go anyways:
Tools needed (all free): - QGIS - LASTools
Lidar's just an x, y, and z coordinate turned into a point cloud, so if you can create a text file which looks like: x y z 1003 5929 14.36 1004 5932 14.69
...
The workflow: - download a DEM, the more precise the better.
- convert your DEM to a vector points file using QGIS/GRASS r.to.vect in the processing toolbox. - export your vector points file as a csv file using QGIS. QGIS will also export the X/Y geometry automatically - this step is a little bit tricky (you'll want to export TAB instead of COMMA and make sure nothing is quoted) but your end goal is a file with x y z as the three columns. - use the txt2las tool to convert your xyz csv file into a LIDAR file
- classify your LIDAR file by running the lasground tool - otherwise Chad's tool won't find it
You should now have a new LIDAR file that you can import into Chad's tool.
This isn't straightforward and I've done a horrible job explaining it, but I hope it can help someone.
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Post by sandgroper on Jan 20, 2023 8:07:10 GMT -5
Thanks statto, I’ve been playing around with DEM files for a while, but never managed to crack the secret. I’ll give it a go on my test plot and see what happens. |
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Post by statto on Jan 20, 2023 10:56:56 GMT -5
It's not an easy workflow, but it's definitely possible. I'm still playing around with it a bit, I haven't quite gotten a completed course yet, there's just a little bit of an offset.
If you have contours from say a course book, you can draw those in as lines, convert the line to points (technically you'd run a function to randomly add points along the line, which is easily done in QGIS), and then merge the DEM points cloud with your green contours points cloud, which would give you better accuracy around the greens.
I've also been able to create a fictional course using contours but haven't been able to align the elevation with the fictional osm file yet. I'm very close though, both import correctly but aren't aligned.
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Post by sandgroper on Jan 20, 2023 20:12:00 GMT -5
Does playing with the offsets in Chad’s tool make any difference?
I’ve seen osm traces that don’t line up and there is the ability to “move” the LiDAR data around.
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Post by statto on Jan 24, 2023 6:17:58 GMT -5
Does playing with the offsets in Chad’s tool make any difference? I’ve seen osm traces that don’t line up and there is the ability to “move” the LiDAR data around. I'm working with fictional data, so my issue is that the projection doesn't match the OSM data because I tried to do something tricky that didn't work. Trying to fix it now.
UPDATE: It was just a projection problem.
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