THSNPOLY

Description

Creates a Thiessen polygon channel (Voronoi diagram) from an input point layer.

Parameters

thsnpoly(fili, filo, dbvs, usegeo, srcattr)

Name	Type	Caption	Length	Value range
FILI *	str	Input file name	1 -
FILO	str	Output file name	0 -
DBVS *	List[int]	Input vector segment	1 - 1
USEGEO	str	Use Georeferencing	0 - 3	ON | OFF Default: OFF
SRCATTR	str	Source attributes	0 - 4	COPY | JOIN Default: COPY

* Required parameter

Parameter descriptions

FILI

Specifies the input PCIDSK file that contains the point layer from which the Thiessen polygons will be constructed.

FILO

Specifies the name of the PCIDSK image file to receive the Thiessen polygons from the point segment. If the specified output file does not exist, THNSPOLY creates it.

DBVS

Specifies the vector segment that contains the point layer for which the Thiessen polygons will be constructed.

USEGEO

Specifies whether the use Georeferencing from the input file to calculate the projection and geographic extents of the resulting polygon layer.

SRCATTR

Specifies whether the attributes from the source layer are copied or joined to the point layer.

Details

THSNPOLY takes an input point layer and generates a Thiessen polygon layer. A Thiessen polygon, or Voronoi diagram, defines a polygon about a point such that all locations within the polygon are closer to that point than to any other point. In the THSNPOLY function, one polygon is generated for each input point.

The attributes for the polygon layer, which include area, perimeter, and the attributes from the original layer, are either copied to the new layer or joined (linked) to the original layer. If joined, an attribute named "SourceID" will be added as the join field.

The extents of the generated layer are determined from either the input point layer (+ 10%) or from an optional georeferencing input.

Raster Thiessen polygons can be generated using the GRDPIN function, although you must enter a parameter value of 1 for "Number of sample Points".

This function can be used to model zones of influence.

Example

The following example create a Thiessen polygon layer in the file "output.pix", based on point layer 32 in the file "irvine.pix".

from pci.thsnpoly import thsnpoly

fili	=	'irvine.pix'	# input file name
filo	=	'output.pix'	# will be created
dbvs	=	[32]	# vector segment containing point layer
usegeo	=	''	# default, "OFF"
srcattr	=	''	# default, "COPY"

thsnpoly( fili, filo, dbvs,usegeo, srcattr )