R lidR compute tree crown width

I have a LiDAR tile with segmented which includes respective tree `IDs` using `silva2016`. Now, I am looking for a way to compute the `crown widths` of each of the segmented trees.

How or which metric can I use to do this?

Purpose: In `ArcGIS Pro 3` you can use the `Draw preset layers` tool to render `Realistic Trees` in `3D` on a map. This tool requires height and crown width information of each tree. I have `ztop` but don't have the crown width information.

Area:

ITD:

Segmented LAS via `silva2016`:

Draw preset layers

Code:

``````library(lidR)

LAS_TreeID = segment_trees(LAS ,
silva2016(CHM_pitfree,
CHM_pitfree.TTops_Manual2)) # segment point cloud
``````
• First, you must define what is the "radius" of set of points that is not circular. Once you have a definition that fits your needs I may be able to help you. But without a definition there are hundreds of possible answers.
– JRR
Sep 23, 2022 at 20:01
• @JRR the documentation of the tool refers to it as `crown width` (Section `Realistic Trees`) Sep 23, 2022 at 20:30
• @JRR any updates? Sep 26, 2022 at 11:50

1 Answer

In absence of a clear definition of the radius/width of objects that are not circular we can assume they are almost circular i.e. the convex hull of each tree is not to far from a circle. In this case the radius can be approximated by `sqrt(A/pi)`.

``````library(lidR)
LASfile <- system.file("extdata", "MixedConifer.laz", package="lidR")
trees <- readLAS(LASfile, filter = "-drop_z_below 0")
metrics <- crown_metrics(trees, .stdtreemetrics)
metrics\$radius = sqrt(metrics\$convhull_area/pi)
``````

For a more complex definition, we need... a definition.

• So I should ask `ESRI` what they mean by `Crown Width`? Sep 26, 2022 at 13:21
• No, I think they mean exactly what they mean. The width is the diameter to plot circular objects. But you want to extract the diameter of something that is not circular. It could be the diameter the largest circle that includes all points. Or another circle that "fits" one the points. Or something else.
– JRR
Sep 26, 2022 at 13:27
• Hi JRR, hope all is well, so what are the default units for `convhull_area`? Let's say the LiDAR units are in `feet` then the units for `convhull_area` would be `square feet` right? Dec 7, 2023 at 16:02
• In the units of the point cloud.
– JRR
Dec 7, 2023 at 16:04