Qgis - modeler and LAStools problem

[Fausto Ugozzoli]

Hi, I'm testing this beautiful procedure in the modeler for ITD  Individual Tree Detection   / CHM as found here:

http://wiki.awf.forst.uni-goettingen.de/wiki/index.php?title=Individual_Tree_Detection_(ITC)&oldid=14047

But, while the second part is working properly, the output of the first algorithm (lasground) is not going to the input of the second (lasheight), and so on...

Any guess? 

Best regards

[Jesse Johnson]

What version of QGIS are you using?  What is the readout in the Log tab when lasheight fails?  Are you running this on a Windows computer?

[Fausto Ugozzoli]

Hi Jesse!

• QGIS: 3.16.0-Hannover (dark background colors)
• log attached: the first algorithm (lasground) creates a temp otuput, (or a real output if I choose to save a file) then in the second alg. , the input appears empty in the log (I think..), so nothing in output...in the log you found also the subsequent steps that end with the creation of the CHM.tif (not created).
• Windows 10 computer. (the LAStools algorithm works perfectly INDIVIDUALLY, also works well the second part of the model with SAGA algorithms and others)

Thank you for your time.

[Jesse Johnson]

On a quick first look of your log file I would say that the problem is being caused by ITC_detection.model setting the 'spike_free' flag as it tries to execute blast2dem.  If we work through the algorithm step by step we are using las2dem, not blast2dem, and I have not found any examples of using 'spike_free' with the latter.

You can try running the ITC_detection.model with a much smaller laz file and see if you have the same issue, it seems that I read somewhere that las2dem works well with files that have less than 20 million points.

I would be curious to find out if the spike free algorithm can be used with blast2dem, or why it would not be needed while working with larger files.

[Martin Isenburg]

Hello,

The spike-free algorithm is only implemented in las2dem. It's not trivial  to "stream" it so I doubt there will be an implementation in BLAST unless I take a research sabbatical. However, the original "pit-free" algorithm can be used with blast2dem (assuming you work with an already normalized LiDAR data set).

https://rapidlasso.com/2014/11/04/rasterizing-perfect-canopy-height-models-from-lidar/

Regards.

Martin

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[Jesse Johnson]

Thanks for the information Martin, the pit-free algorithm will certainly be something I can use going forward.

Cheers,

  Jesse

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[Jesse Johnson]

Hi Fausto,

I was able to make contact with someone at AWF that provides the ITC_detection.model you are working with it only works with QGIS 2; besides the blast2dem issue we were seeing, there may be some issues with SAGA in QGIS 3 that require some troubleshooting.  I sure didn't notice problems with SAGA during my initial work through of the model, but after revisiting the project I noticed there may be problems with the seeds,shp file being produced although that may just be a problem on my end, I haven't taken the time to sort through it yet.

Cheers,

  Jesse

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[Fausto Ugozzoli]

Hi Jesse,

thamkyou for the usefull info, all clear about spike-free and Blast..
About SAGA and seeds.shp creation, in the second part of the pipeline, (also the creation of segments.shp with polygonize at the end) all is working properly for me.

The problem I encounter is between first (lasground) and second (lasheight) step, I get output only from first step, therefore the pipeline is interrupted. I'll try with your previous suggestions (also testing with qgis 2) and I'll give an update ASAP!

Have a nice day,

Fausto