How to create model key points using LAStools?

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Jim Peterson

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Jan 8, 2016, 4:09:34 AM1/8/16
to LAStools - efficient tools for LiDAR processing
I realize that a user can contour from model key points.  However, I am wondering if LAStools can be used to automatically and/or semi-automatically create model key points?  Thank you in advance for any answers.  

Seweryn Cieslik

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Jul 14, 2016, 8:53:08 AM7/14/16
to LAStools - efficient tools for LiDAR processing
Hi
I wonder if you got a reply to this question?

Regards

Tobias K Kohoutek

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Jul 14, 2016, 11:00:40 AM7/14/16
to LAStools - efficient tools for LiDAR processing
Hi Jim,

I guess my first question would be: What's a model key point by definition for the client?
I found once a PowerPoint presentation where the definition was close to "points that represent ISO lines". Not sure if that's the case or if it would be more like the representation of the grid cell of the DTM.

Kind of simple idea if it would be the latter and your DTM is stored in a text file, then you could just use text2las and by my simple thinking the resulting las cloud should represent 1 point per grid cell which is definitely less dense than the original cloud. If I'm thinking wrong I apprecheate every correction. If however you want those points that represent the ISO lines, then for now I've in my mind only that you could use ArcGIS or QGIS and load your ISO lines and original point cloud and then search for points which are close to the line features ( <10cm) and generate a new point file.

So how would you define Model Key Points?

Cheers, 
Tobias

Martin Isenburg

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Jul 20, 2016, 6:29:45 AM7/20/16
to LAStools - efficient command line tools for LIDAR processing
Hello,

you can create keypoints with the latest version of lasthin as mentioned in this thread:

http://groups.google.com/d/topic/lastools/feVaDmjGPXA/discussion

Via the option '-adaptive 0.2' lasthin will allow "adaptive thinning" based on a vertical tolerance of, for example, 20 centimeters. Here are the command lines that are available for this in the current release of LAStools.


Here an example:

lasthin -i ..\data\fusa.laz ^
            -ignore_class 1 3 4 5 6 7 ^
            -adaptive 0.2 ^
            -classify_as 8 ^
            -o fusa_classified_keypoints.laz

will produce a new version of the venerable "fusa.laz" where the "most important" ground points (classification code 2) are reclassified as keypoints (classification code 8). Here th same but flagging those points as keypoints instead of reclassifying them:

lasthin -i ..\data\fusa.laz ^
            -ignore_class 1 3 4 5 6 7 ^
            -adaptive 0.2 ^
            -flag_as_keypoint ^
            -o fusa_flagged_keypoints.laz

Re can get a coarser version of only ground and buildings using

lasthin -i ..\data\fusa.laz ^
            -keep_class 2 6 ^
            -adaptive 0.2 ^
            -o fusa_thinned_ground_buildings.laz

I have attached two screenshots for the result that the last command line is getting.



lasthin_new_adaptive_thinning_1.jpg
lasthin_new_adaptive_thinning_2.jpg
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