Shape complexity index

This tool provides a measure of overall polygon shape complexity, or irregularity, for both raster and vector features. Several shape indices have been created to compare a polygon's shape to simple Euclidean shapes (e.g. circles, squares, etc.). One of the problems with this approach is that it inherently convolves the characteristics of polygon complexity and elongation. The Shape Complexity Index (SCI) was developed as a parameter for assessing the complexity of a polygon that is independent of its elongation. In fact, the SCI has a different definition for vector polygons and raster polygons. For vector features, SCI relates a polygon's shape to that of an encompassing convex hull. It is defined as:

SCI = 1 - A / Ah

Where where A is the polygon's area and Ah is the area of the convex hull containing the polygon. Convex polygons, i.e. those that do not contain concavities, have a value of 0. As the shape of the polygon becomes more complex, the SCI approaches 1. Note that polygon shape complexity also increases with the greater number of holes (i.e. islands), since holes have the effect of reducing the lake area. The SCI values calculated for each vector polygon feature will be placed in the accompanying database file (.dbf) as a complexity field (COMPLEXITY). The resulting database file will be displayed automatically after the tool has completed.

For raster polygons, the SCI is the average number of line intersections with polygon boundaries averaged for the N-S, E-W, NW-SE, and NE-SW directions. Convex polygons will have a value of 2 and more irregular shaped polygons, including those containing holes, will have higher values. The input raster grid should contain polygons with unique identifiers greater than zero. The user must also specify the name of the output raster file (where the radius of gyration will be assigned to each feature in the input file) and the specified option of outputting text data.

See Also:


The following is an example of a Python script that uses this tool:

wd = pluginHost.getWorkingDirectory()
inputFile = wd + "polygons.shp" # vector input
outputFile = "" # ignored for vector input
textOutput = "false" # also ignored
args = [inputFile, outputFile, textOutput]
pluginHost.runPlugin("ShapeComplexityIndex", args, False)

This is a Groovy script also using this tool:

def wd = pluginHost.getWorkingDirectory()
def inputFile = wd + "polygons.dep" // raster input
def outputFile = wd + "output.dep"
def textOutput = "true"
String[] args = [inputFile, outputFile, textOutput]
pluginHost.runPlugin("ShapeComplexityIndex", args, False)