Module Openness

opals::IOpenness

# Aim of module

Provides a raster map of local viewsheds (i.e. openness) based on a DTM grid model.

# General description

Openness is a measure introduced by Yokoyama (c.f. references). It is an angular measure denoting the aperture angle of a cone centered at a grid point and constrained by the neighboring elevations within a specified radial distance. It is basically a convexity/concavity measure calculated from local terrain profiles in eight directions of the wind. A distinction is made between positive and negative openness (viewshed above and below the terrain).

# Parameter description

-inFileinput grid file
Type: opals::Path
Remarks: mandatory
The input grid file is expected in a GDAL supported data format.
-outFileoutput raster file
Type: opals::Path
Remarks: estimable
Path of openness raster map file in GDAL supported format.
Estimation rule: The current directory and the name (body) of the input file are used as file name basis. Additionally, a postfix and the extension according to the specified output format are constructed (e.g. '_open.tif').
-oFormatraster file format [GTiff,AAIGrid,SCOP,...]
Type: opals::String
Remarks: estimable
Use GDAL driver names like GTiff, AAIGrid, USGSDEM, SCOP... .
Estimation rule: The output format is estimated based on the extension of the output file (*.tif->GTiff, *.dem->USGSDEM, *.dtm->SCOP...).
-featureopenness type
Type: opals::OpennessFeature
Remarks: default=positive
Possible values:
positive ... positive openness
negative ... negative openness

Openness is defined as positive and negativeOpenness See module docu for further details.
-selModeselection mode (0=mean,1=min,2=max)
Type: int32
Remarks: default=0
For a specific pixel, the openness is calculated based on local grid profiles in eight directions of the wind. Thus, the resulting openness value can either be calculated as the mean (=0), minimum (=1), or maximum(=2) of all valid openness values (i.e. opening angle of a cone)
-kernelSizekernel size (radius of kernel in pixels)
Type: int32
Remarks: default=5
-limit2D clipping window
Type: opals::GridLimit
Remarks: optional
If no user defined limits are specified or -limit is even skipped, the entire xy-extents of the input raster model are used.
GridLimit: Defines xy-limits for output grid/raster datasets. The limit coordinates specified by left/lower/right/upper either refer to pixel centers (default) or corners, and may optionally get rounded to multiples of the grid size.
Syntax: ['center'|'corner']['round']['(' left lower right upper ')']
-noDatanodata value
Type: float
Remarks: default=9999
Value representing an undefined value in the output raster model

# Examples

This example shows how to derive an openness map based on the surface model of demo data set strip21.laz located in the \$OPALS_ROOT/demo/ directory. To generate the DSM, please perform the following preprocessing steps:

opalsImport -inFile strip21.laz
opalsGrid -inFile strip21.odm -outFile strip21.tif -gridSize 1 -interpolation movingPlanes

To calculate the positive openness map, type:

opalsOpenness -inFile strip21.tif

Since no further parameters are specified, the default kernel size (5 pixel radius) is considered and each openness pixel is calculated as the mean value of all 8 profile directions resulting in the GTiff file strip21_pos_open_mean.tif.

To calculate a negative openness map using a kernel radius of 7 pixels for each pixel and using the profile with the minimum opening angle, type:

opalsOpenness -inFile strip21.tif -outFile strip21_negOpen_k7.tif -feature negative -kernelSize 7

To visualize the resulting map as a grey-tone image, execute:

opalsZColor -inFile strip21_negOpen_k7.tif -palFile greyPal.xml -nClasses 100

The following output is produced:

Negative openness map

# References

Yokoyama, R., M. Shirasawa, and R. J. Pike: Visualizing Topography by Openness: A New Application of Image Processing to Digital Elevation Models, Photogrammetric Engineering and Remote Sensing(68), No. 3, March 2002, pp. 25799866.

G. Mandlburger, M. Vetter, M. Milenkovic, N. Pfeifer: "Derivation of a countrywide river network based on Airborne Laser Scanning DEMs - results of a pilot study"; 19th International Congress on Modelling and Simulation. Perth, Australia; 2011 in: "Modelling and Simulation Society of Australia and New Zealand", (2011), ISBN: 978-0-987214399-7; 2423 - 2429.

opalsZColor is the executable file of Module ZColor
Definition: ModuleExecutables.hpp:248
opalsOpenness is the executable file of Module Openness
Definition: ModuleExecutables.hpp:153
@ movingPlanes
moving (tilted) plane interpolation
opalsImport is the executable file of Module Import
Definition: ModuleExecutables.hpp:113
@ kernelSize
output grid size equals entire kernel size
opalsGrid is the executable file of Module Grid
Definition: ModuleExecutables.hpp:93
@ nClasses
number of different classes (e.g. opalsZColor)
@ feature
Use a statistic feature of the boundary gap points for filling.
@ negative
negative openness
@ palFile
palette file (opalsZcolor)