Jessica M.
New Member
Posts:  
| 04 Jan 2018 03:56 PM |
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I am a M.S. student and plan on using ENVI Lidar as part of my thesis research in estimating tree height/canopy cover from Lidar data.
I am not sure if the information is proprietary, but is there a way to find out/better understand how ENVI Lidar calculates the tree heights as part of processing the data? I cannot seem to find information on the algorithm.
Any information would be helpful and thank you!
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MariM
Veteran Member
Posts:2396 
| 15 Jan 2018 09:38 AM |
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The equations are proprietary but here is a high level description that might be helpful:
• Points are classified as terrain, building, powerline or tree (vegetation)
• The vegetation points are analyzed to find tree crowns by finding the highest vegetation point in a local area and checking if the points slope downward and outwards from this point. This calculation yields the crown center and radius.
• Where a tree crown was detected the ground height under it is determined from the DEM and the tree height calculated by subtracting the ground height from the highest point in the tree crown.
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Srijani Mukherjee
New Member
Posts:2
| 02 Oct 2019 12:42 PM |
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Hi, I had a similar question and this answer helped a lot! I am curious if ENVI+IDL will be enough to create the CHM? If not what module should I use to do the same? And what's the price of the student license for it?
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MariM
Veteran Member
Posts:2396
| 03 Oct 2019 06:09 AM |
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ENVI Lidar can create a DEM and DSM to create the CHM (canopy height model).
You can purchase a student license online here in the US: https://www.harrisgeospatial.com/Industry-Solutions/Academic#students
Or you can purchase through your local distributor: https://www.harrisgeospatial.com/Company/Contact-Us
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Srijani Mukherjee
New Member
Posts:2
| 10 Oct 2019 09:21 AM |
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I purchased the student license but it didn't come with DSM and DEM modules. Is there any other way to build the DEM and DSM?
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MariM
Veteran Member
Posts:2396
| 10 Oct 2019 10:23 AM |
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ENVI Lidar is included with ENVI and can generate a DSM or DEM from lidar data. This is not the same as the DEM Extraction module which generates a DEM from stereo imagery and requires an ENVI DEMEx license or the Generate Pointcloud and DSM tool that generates a pointcloud and DSM also from stereo imagery and requires the Photogrammetry module.license.
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