Tool Polygon Shape Indices
The tool calculates various indices describing the shape of polygons, mostly based on area, perimeter and maximum diameter. If the optional output 'Shape Indices' is not created, the tool attaches the attributes to the input dataset. Otherwise a new dataset is created and attributes existing in the input dataset are dropped.
- A area
- P perimeter
- P/A interior edge ratio
- P/sqrt(A)
- Deqpc equivalent projected circle diameter (=2*sqrt(A/pi))
- Sphericity the ratio of the perimeter of the equivalent circle to the real perimeter (=(2*sqrt(A*pi))/P)
- Shape Index the inverse of the sphericity (=P/(2*sqrt(A*pi)))
- Dmax maximum diameter calculated as maximum distance between two polygon part's vertices
- DmaxDir direction of maximum diameter
- Dmax/A
- Dmax/sqrt(A)
- Dgyros diameter of gyration, calculated as twice the maximum vertex distance to its polygon part's centroid
- Fmax maximum Feret diameter
- FmaxDir direction of the maximum Feret diameter
- Fmin minimum Feret diameter
- FminDir direction of the minimum Feret diameter
- Fmean mean Feret diameter
- Fmax90 the Feret diameter measured at an angle of 90 degrees to that of the Fmax direction
- Fmin90 the Feret diameter measured at an angle of 90 degrees to that of the Fmin direction
- Fvol the diameter of a sphere having the same volume as the cylinder constructed by Fmin as the cylinder diameter and Fmax as its length
References
- Forman, R.T.T. & Godron, M. (1986): Landscape Ecology. Cambridge.
- Lang, S. & Blaschke, T. (2007): Landschaftsanalyse mit GIS. Stuttgart.
- Merkus, H.G. (2009): Particle Size Measurements: Fundamentals, Practice, Quality. Springer. https://link.springer.com/book/10.1007/978-1-4020-9016-5.
- Author: O.Conrad (c) 2008
- Menu: Shapes|Polygons
Parameters
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Shapes | Shapes, input | SHAPES | - | - |
| Output | Shape Indices (*) | Shapes, output, optional | INDEX | Polygon shapefile with the calculated indices. | - |
| Maximum Diameter (*) | Shapes, output, optional | DMAX | Line shapefile showing the maximum diameter. | - |
| Options | Diameter of Gyration | Boolean | GYROS | - | Default: 0 |
| Feret Diameters | Boolean | FERET | - | Default: 0 |
| Number of Directions | Integer | FERET_DIRS | Number of directions (0-90) to be analyzed. | Minimum: 2
Default: 18 |
| (*) optional |
Command-line
Usage: saga_cmd shapes_polygons 7 [-SHAPES <str>] [-INDEX <str>] [-DMAX <str>] [-GYROS <str>] [-FERET <str>] [-FERET_DIRS <num>]
-SHAPES:<str> Shapes
Shapes, input
-INDEX:<str> Shape Indices
Shapes, output, optional
-DMAX:<str> Maximum Diameter
Shapes, output, optional
-GYROS:<str> Diameter of Gyration
Boolean
Default: 0
-FERET:<str> Feret Diameters
Boolean
Default: 0
-FERET_DIRS:<num> Number of Directions
Integer
Minimum: 2
Default: 18