Problem with LIDAR data processing

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Isida

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Feb 23, 2018, 4:03:34 AM2/23/18
to LAStools - efficient tools for LiDAR processing

Hello!


I am working with LIDAR data of an Italian Region for my PhD and I am facing a lot of problem with them.

My objective is to obtain a DEM and a DSM from this data. I am using lastools on ArcMap 10.3.


First, I tried to understand my data. I have more than one strip for the same area, in the same date, with different number of cloud point. Looking to the classification I discovered that there are 4 classes determined based on the pulse return. 

Thus, the first return is set, as unclassified (which lead to more than a half of the cloudpoints unclassified), the second return is classified as ground, the 3th return as low vegetation and the 4th as medium vegetation. The data do not have a last return. 


Looking to the classification it is incorrect. It is easily detect from a quick overview of the area but also when I tried to obtain a DEM using these classification. This is the process I followed to built a DEM (lasground - lasheight - las2dem) but also using (las to multipoint - point to raster) the result was the same as shown in the screenshot nr. 1. I am missing a lot of points and also I have a lot of noisy points classify as ground. 


Thus. I am trying to reclassify the data but, it looks impossible.


Here the steps that I followed:

  1. ·         Laz to las
  2. ·         las2las(project) (I determined the coordinate system of my data)
  3. ·         lasmerge (I merged all the strips)
  4. ·         lasduplicate (I removed the possible duplicate point with the same xyz)

Then I tried to classify by selection in ARCMAP 10.3 and change codes but they didn’t. Moreover when I used las2las(filter) to drop the classification, it didn't. I am afraid that something is wrong with this data but I don't know what it is.


This is how my original LIDAR data looks in 3D view and if I try to make a Profile view from my las dataset in ArcMap I will obtain a vertical line. As shown in the screenshot nr2. (from ArcMap) and screenshot nr.3 (LIDAR360 software) they are strange although they have a z value that has also negative values (-200). Now I suppose the z value is not sort correctly but I am not sure about this.


Can anyone help me to solve these problem?

Thanks!

 

Screenshot_1.JPG
Screenshot_2.JPG
Screenshot_3.JPG

Martin Isenburg

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Mar 7, 2018, 3:10:05 PM3/7/18
to LAStools - efficient command line tools for LIDAR processing
Hello Isida,

It is not easy to assist you without a *lot* more info about your data. But i see a lot of low noise points and those may affect the ground point classification in a negative way. So that would require the use of lasnoise.

Also, of you have multiple input files that are flightlines or flightstrips then you should first use lastile and create a tiling of square tiles with buffer from your input.

Maybe send us a lasinfo report of 2 or 3 files and we can get a better Idea. I really doubt that your data has no last return points ...

Regards,

Martin

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