Points2Grid

Proven through thousands of jobs run via the OpenTopography Facility (http://www.opentopography.org), Points2Grid is a robust and scalable tool that generates Digital Elevation Models (DEM) using a local gridding method. The local gridding algorithm computes grid cell elevation using a circular neighbourhood defined around each grid cell based on a radius provided by the user. This neighbourhood is referred to as a bin, while the grid cell is referred to as a DEM node. Up to four values — minimum, maximum, mean, or inverse distance weighted (IDW) mean — are computed for points that fall within the bin. These values are then assigned to the corresponding DEM node and used to represent the elevation variation over the neighbourhood represented by the bin. If no points are found within a given bin, the DEM node receives a value of null. The Points2Grid service also provides a null filing option, which applies an inverse distance weighted focal mean via a square moving window of 3, 5, or 7 pixels to fill cells in the DEM that have null values. The local gridding approach employed by Points2Grid is most effective in situations where LIDAR shot densities exceed the resolution of the grid to be produced from these data. Please direct all feedback to [email protected]

INSTALLATION

Please read the INSTALL file for details on the installation process.

USE

If your pre-requisites (curl and liblas) are installed on non-standard location, please set your LD_LIBRARY_PATH accordingly. To run complete usage information, please type "points2grid" from the command-line. The command-line options are as follows:

% ./interp [-i <data_file_name> | -l <data_file_url>] -o <output_file_name> [--input_format=ascii|las] [--all] [--min] [--max] [--mean] [--idw] [--den] [--fill|--fill_window_size=] [-r <search_radius>] [--output_format=all|arc|grid] [--resolution=|--resolution-x=|--resolution-y=]

1. -i <data_file_name> | -l <data_file_url>:

   • must be unzipped plain text file

2. -o <output_file_name>:

   • without extension, i.e. if you want the output file to be test.asc, this parameter shoud be "test"

3. Output Type: --min: the Zmin values are stored --max: the Zmax values are stored --mean: the Zmean values are stored --idw: the Zidw values are stored --den: the density values are stored --all (default): all the values are stored

4. -r

   • specifies the search radius. The default value is square root 2 of horizontal distance in a grid cell

5. --input_format: - 'ascii' expects input point cloud in ASCII format (default) - 'las' expects input point cloud in LAS format

6. --output_format:

   • 'all' generates every possible format,
   • 'arc' for ArcGIS format,
   • 'grid' for Ascii GRID format,
   • the default value is --all

7. Resolution

   • --resolution=: The resolution is set to the specified value. Use square grids.
   • --resolution-x= --resolution-y=: Each parameter specifies each side of grid cells.
   • If not specified, default values (6ft) are used.

8. Null Filling --fill: fills nulls in the DEM. Default window size is 3. --fill_window_size=: The fill window is set to value. Permissible values are 3, 5 and 7.