FANR5640/7640: Lecture 15 – It Is Friday…


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Improvement of clip by extent example from Wednesday…  The following code clips the LAS to the boundary of the shapefile.  (example data)

library(lidR)
library(rgdal)

setwd("c:/temp/sf/")
tdat<- readLAS("sp2_pcloud.las")
plot(tdat)

tpoly<- readOGR( ".","AnalysisUnit")

clpdat <- lasclipPolygon(tdat,
 tpoly@polygons[[1]]@Polygons[[1]]@coords[,1],
 tpoly@polygons[[1]]@Polygons[[1]]@coords[,2])

plot(clpdat)

 

 

COARSE WOODY DEBRIS EXAMPLE:

Task at hand is to determine the volume (m3) of the oriented pile shown in the following image.

SUPPORTING INFORMATION:

The volume of a cylindrical object is misrepresented in rasterized products derived from nadir imagery (as seen above). The surface of visible objects are represented true-to-form while the parts not visible in the image are squared (figure 1). We will use a correction factor of 0.8798 to correct our estimates.

C:\Users\dell\Desktop\vol_est.jpg

Figure . Example of how UAV imagery views stems and CWD.

See Brian Davis’ thesis, Refinement of a drone-based method for estimating coarse woody debris and biomass residue following forest harvest, for more background, procedures, and project results (https://athenaeum.libs.uga.edu/handle/10724/37140).

GLOBAL MAPPER WORKFLOW:

  • Clip LAS to pile’s boundary
  • Classify ground surface
  • Isolate stems

Clip LAS in Global Mapper

  • MAKE A BACKUP OF YOUR LAS FILE (copy/paste in Windows Explorer)
  • Load LAS & polygon shapefile boundary
  • Select LAS points
    • Use Digitizer tool to select polygon boundary
      • Turn on ONLY boundary layer
      • Select digitizer tool (icon with pencil)
      • Click on polygon
    • Turn on the point cloud layer
    • Right-click on polygon > Advanced Selection Options > Select all Point Features within the Selected Area(s)
  • Invert selection
    • Turn on ONLY LAS layer
    • Right-click > Advanced Selection Options > Invert Selection
  • Delete selected (points not in polygon)
    • Righ-click > Delete – Delete Selected Feature(s)

… Continued…