writers.gdal

The GDAL writer creates a raster from a point cloud using an interpolation algorithm. Output is produced using GDAL and can therefore use any driver that supports creation of rasters.

The technique used to create the raster is a simple interpolation where each point that falls within a given radius of a raster cell center potentially contributes to the raster’s value.

Note

If a circle with the provided radius doesn’t encompass the entire cell, it is possible that some points will not be considered at all, including those that may be within the bounds of the raster cell.

The GDAL writer creates rasters using the data specified in the dimension option (defaults to Z).The writer will creates up to six rasters based on different statistics in the output dataset. The order of the layers in the dataset is as follows:

min
Give the cell the minimum value of all points within the given radius.
max
Give the cell the maximum value of all points within the given radius.
mean
Give the cell the mean value of all points within the given radius.
idw
Cells are assigned a value based on Shepard’s inverse distance weighting algorithm, considering all points within the given radius.
count
Give the cell the number of points that lie within the given radius.
stdev
Give the cell the population standard deviation of the points that lie within the given radius.

If no points fall within the circle about a raster cell, a secondary algorithm can be used to attempt to provide a value after the standard interpolation is complete. If the window_size option is set to a non-zero value, a square of rasters surrounding an empty cell, and the value of each non-empty surrounding is averaged using inverse distance weighting to provide a value for the subject cell. The value provided for window_size is the maximum horizontal or vertical distance that a donor cell may be in order to contribute to the subject cell (A window_size of 1 essentially creates a 3x3 array around the subject cell. A window_size of 2 creates a 5x5 array, and so on.)

Cells that have no value after interpolation are given the empty value of -9999.

Basic Example

This pipeline reads the file autzen_trim.las and creates a Geotiff dataset called outputfile.tif. Since output_type isn’t specified, it creates six raster bands (“min”, “max”, “mean”, “idx”, “count” and “stdev”) in the output dataset. The raster cells are 10x10 and the radius used to locate points whose values contribute to the cell value is 14.14.

{
  "pipeline":[
    "pdal/test/data/las/autzen_trim.las",
    {
      "resolution": 10,
      "radius": 14.14,
      "filename":"outputfile.tif"
    }
  ]
}

Options

filename
Name of output file. [Required]
resolution
Length of raster cell edges in X/Y units. [Required]
radius
Radius about cell center bounding points to use to calculate a cell value. [Required]
gdaldriver
Name of the GDAL driver to use to write the output. [Default: “GTiff”]
gdalopts

A list of key/value options to pass directly to the GDAL driver. The format is name=value,name=value,... The option may be specified any number of times.

Note

The INTERLEAVE GDAL driver option is not supported. writers.gdal always uses BAND interleaving.

output_type
A comma separated list of statistics for which to produce raster layers. The supported values are “min”, “max”, “mean”, “idw”, “count”, “stdev” and “all”. The option may be specified more than once. [Default: “all”]
window_size
The maximum distance from a donor cell to a target cell when applying the fallback interpolation method. See the stage description for more information. [Default: 0]
dimension
A dimension name to use for the interpolation. [Default: Z]