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Extraction des arbres à partir de LiDAR et du DSM dérivé

JonnyWilks

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Bonjour à tous,<\/P>

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Je suis relativement nouveau dans le domaine d'ArcGIS et je réalise actuellement un projet de master visant à extraire les arbres afin d'identifier les changements dans le stockage du carbone des forêts urbaines au fil du temps en utilisant des données LiDAR. Pour éliminer la petite végétation du DSM normalisé dérivé, j'ai appliqué une fonction conditionnelle qui a supprimé les pixels <3m.<\/P>

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Le problème que je rencontre est que je ne trouve pas de moyen pour différencier les arbres des bâtiments dans la couche raster résultante. Malheureusement, les codes de classe ont été incorrectement attribués dans les données LAS originales, ce qui signifie que tout a été classé comme végétation, donc je ne pouvais pas utiliser les codes pour extraire la végétation. <\/P>

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Existe-t-il d'autres méthodes pour extraire la végétation en utilisant uniquement les données LiDAR ou les DSM ? Toute aide serait grandement appréciée !<\/P>

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Merci<\/P>

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Jonny<\/P><\/BODY><\/HTML>

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ArthurCrawford01

Hello Fabio,

It would be good for getting a rough estimate of trees per the acre of a certain size. It will not get the under canopy trees. If you paired it with any detailed tree stand information, it could be used to interpolate the trees in other areas. If Trees from Lidar found 150 trees in an acre and the tree stand (detailed tree inventory) finds 300 trees, you could estimate based on number of trees from Trees from lidar x 2.

Fabio_Secanho

Hey Arthur,

I need to estimate trees per acre of an area that I have Lidar data on. I've downloaded your toolbox (Trees From LiDAR) but when I try to open it, I get an error message saying "The tool is not licensed". I have all the necessary licenses and I use ArcGIS Pro 2.7. I don't need to visualize the trees, but only estimate the number of trees per acre. Is this tool appropriated for this task? Any other suggestion on a workflow to accomplish this?

Thank you very much!
Fabio

Kara_Lara

This is an awesome toolset!!! Thank you!

ArthurCrawford01

Hello Jonny,

This is the writer of the blog that Ian Murray referenced and developer of the tool to extract tree points. If you are trying to get volume of trees, I would focus on using the Z-Range method option of the LAS Point Statistics As Raster. Here's the link for it:

https://desktop.arcgis.com/en/arcmap/latest/tools/data-management-toolbox/las-point-statistics-as-raster.htm

http://pro.arcgis.com/en/pro-app/tool-reference/data-management/las-point-statistics-as-raster.htm

This will create a DEM showing the distance between first and last return, it's what I use in the tool Ian mentioned.

Tree Volume .

So the area between the red and the light blue I think is what you are trying to get. Once you create the Z-Range using LAS Point Statistics as Raster, you will need to remap the say -100 to 8 foot as no data. The red and dark blue line shows what will be 0 or no data in the raster using LAS Point Statistics as Raster with Z-Range method. This will give you that area as a raster, then you can use the Surface Volume tool with the plane height set to 0.

https://pro.arcgis.com/en/pro-app/tool-reference/3d-analyst/surface-volume.htm

Hope this helps,

Arthur Crawford - Esri

XanderBakker

The tool will only consider the class code 0 and 1 (Never classified and Unclassified):

JonnyWilks

Thanks for the quick response! I've been able to classify the buildings and ground with the first two tools you mentioned. Following that, how would I extract only the points that remain unclassified in order to run the "Classify LAS By Height" tool?

XanderBakker

In addition there is a toolbox called 3D Sample Tools (see https://www.arcgis.com/home/item.html?id=fe221371b77940749ff96e90f2de3d10 ) that I have used to extract trees from LiDAR data and I used that to create a 3D representation of the trees for the 3D distance to overhead power lines. See blog post here:

https://community.esri.com/people/xander_bakker/blog/2016/07/14/calculating-the-3d-distance-of-trees-derived-from-lidar-data-to-overhead-power-lines

XanderBakker

There is also in ArcGIS Pro the Classify LAS Building—Help | ArcGIS Desktop tool to classify buildings. You could extract the points that remain unclassified (and which are no ground, see Classify LAS Ground—Help | ArcGIS Desktop ) and apply the Classify LAS By Height—Help | ArcGIS Desktop to classify the trees (assuming you don't have electric transmission tower and other objects).

IanMurray

Have a look at this blog, should help get you started.

https://community.esri.com/people/acrawford-esristaff/blog/2016/12/22/arthurs-feature-extraction-from-lidar-dems-and-imagery

Also, does your .las files have intensity values? That is another way to help distinguish rooftops from natural features.(i.e. trees).

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