lasground settings and de-noiseing data

[hairyape1ben]

Hi all,

I have been experimenting with las ground to classify ground points. I am looking for some advice to tune las ground to see if it can produce a more accurate result by using different commands eg -step 0.005 or similar.

The data I have is at a resolution of around 1000 points/ m^2 and it is of an area of forest with dense vegetation.

I am looking for the best representation of the ground points for locating archaeology.

The result I have created look pretty good, but with my limited knowlage of lasground I wonder if I could produce better results by tuning the tool for this situation.

I am also struggling with 'noise' in the data making DEMs seem very busy and difficult to interpret. Viewing the point cloud in lasview I can clearly identify ditched and banks, but these are difficult to locate within raster DEMs. What steps would be best to smooth the data to remove noise?

Or maybe the solution is the project the data in a different format, currently I am creating raster DEMs in QGIS, may a 3D view would be easier to interpret?

Open to any suggestions and guidance.

Thank you

[Martin Isenburg]

Hello,

wow. Is that 1000 pulses per square meter? Or 1000 returns per square meter. I personally dislike the "point per m^2" moniker as it is never clear what the density really is. I prefer the terms "pulses per square meter" or "last returns per square meter" and for the interesting - but never useful on its own - number that specifying how many returns there are per square meter (including first, intermediate, and last) the "total points per square meter" or "all returns per square meter" are more indicative. The latter is only really useful if I know the first and gives me some indication how much multi-interaction the laser beams have had with "stuff" (-> wires, vegetation, birds, green houses, building edges, bicycles, bee swarms, clouds, fences, poles, flying plastic bags, pedestrians,...) below the aircraft.

http://rapidlasso.com/lasground

http://lastools.org/download/lasground_README.txt

http://lastools.org/download/lasground_new_README.txt

That said ... experimenting with all of the parameters in lasground (as well as with lasground_new) ... is your only really option. Have a look at the results reported by Agata Klimczyk but for much lower density data. 

http://groups.google.com/d/topic/lastools/3wh_Ny2XZ8Y/discussion

The visualization and smoothing of the archaeological DTM is another topic. You may want to create DTMs at different resolutions and maybe apply some smoothing with GDAL before creating hillshades with different light lirections and other visualizations that are popular for archaeological discovery,

Also ... for the coarser DTMs ... it may make sense to lower the spacings between the ground points with lasthin before generating the DTM with las2dem.

http://rapidlasso.com/lasthin

http://lastools.org/download/lasthin_README.txt

http://rapidlasso.com/las2dem

http://lastools.org/download/las2dem_README.txt

Regards,

Martin @rapidlasso

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