This tool can be used to interpolate a regular grid raster from a point cloud LiDAR dataset using an inverse-distance-weighted (IDW) interpolation method. The user inputs a LiDAR dataset in LAS file format (.las) and the name of the output raster grid to be created. Although most often this tool will be used to create a digital elevation model (DEM) from the elevation data associated with the LiDAR dataset, the user can also specify a number of other parameters to interpolate including the LiDAR point intensity, classification, and associated red, green, and blue values. Note that not all LiDAR datasets will include each of these parameters. Interpolation can be based on all of the points in the dataset, first return points, or last return points. The user must also specify the IDW exponent, the search radius, and rotation value (if any).
The maximum scan angle deviation parameter can be used to filter points from the neighbourhood around each interpolated grid cell that have scan angles that are larger than the neighbourhood minimum scan angle by this user-defined threshold value. Large variation in the scan angle of nearby LiDAR points can be common near the edges of scan lines. Although the effects of this are rarely apparent in the DEM, the impact of using a collection of points with greatly varying scan angles for interpolation can be observed in the derived products of the DEM, particularly the hillshade image. This can significantly impact modelled surface flowpaths in flight-line edge areas. Lowering the maximum scan angle deviation parameter will have the impact of reducing this artifact. If the parameter is set too low, however, the resulting interpolated surface may contain extensive areas of NoData values. It is not recommended that this parameter be set lower than 3.0 degrees. Similarly, if you do not want to exclude any points as a result of the variation of scan angles within interpolation neighbourhoods, simply set this parameter to a high value, e.g. 90.0 degrees.
Grid cells that have no points within the search radius assigned the NoData value in the output image. The output raster is of the float data type and continuous data scale.
If the LiDAR data you wish to interpolate is not contained in the LAS file format, but rather an ASCII text file, you may use one of the interpolation tools contained in the Raster Creation toolbox to interpolate the dataset.
The following is an example of a Python script using this tool:
wd = pluginHost.getWorkingDirectory()
# You may have multiple input files but they must
# be separated by semicolons in the string.
inputs = wd + "input1.las" + ";" + wd + "input2.las" + ";" + wd + "input3.las"
suffix = "IDW"
interpParameter = "z (elevation"
ptReturn = "all points"
exponent = "2.0"
maxSearchDist = "5.0"
pointsToUse = "8"
gridRes = "1.0"
maxScanAngleDeviation = "3.0"
# excluded points...
neverClassified = "false"
unclassified = "false"
bareGround = "false"
lowVeg = "false"
mediumVeg = "false"
highVeg = "false"
buildings = "false"
lowPoints = "false"
keyPoints = "false"
water = "false"
args = [inputs, suffix, interpParameter, ptReturn, exponent, maxSearchDist, pointsToUse, gridRes, maxScanAngleDeviation,
neverClassified, unclassified, bareGround, lowVeg, mediumVeg,
highVeg, buildings, lowPoints, keyPoints, water]
pluginHost.runPlugin("LiDAR_IDW_interpolation", args, False)
This is a Groovy script also using this tool:
def wd = pluginHost.getWorkingDirectory()
// You may have multiple input files but they must
// be separated by semicolons in the string.
def inputs = wd + "input1.las" + ";" + wd + "input2.las" + ";" + wd + "input3.las"
def suffix = "IDW"
def interpParameter = "intensity"
def ptReturn = "last return"
def exponent = "2.0"
def maxSearchDist = "5.0"
def pointsToUse = "8"
def gridRes = "1.0"
def maxScanAngleDeviation = "5.0"
// excluded points...
def neverClassified = "false"
def unclassified = "false"
def bareGround = "false"
def lowVeg = "false"
def mediumVeg = "false"
def highVeg = "false"
def buildings = "false"
def lowPoints = "false"
def keyPoints = "false"
def water = "false"
String[] args = [inputs, suffix, interpParameter, ptReturn, exponent, maxSearchDist, pointsToUse, gridRes, maxScanAngleDeviation,
neverClassified, unclassified, bareGround, lowVeg, mediumVeg,
highVeg, buildings, lowPoints, keyPoints, water]
pluginHost.runPlugin("LiDAR_IDW_interpolation", args, false)