THSNPOLY

Description

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

Parameters

Name	Type	Caption	Length	Value range
FILI *	String	Input file name	1 - 192
FILO	String	Output file name	0 - 192
DBVS *	Integer	Input vector segment	1 - 1
USEGEO	String	Use Georeferencing	0 - 3	ON | OFF Default: OFF
SRCATTR	String	Source attributes	0 - 4	COPY | JOIN Default: COPY
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* 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.

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

• ON: Turns the monitor ON (default)
• OFF: Turns the monitor OFF (recommended if running in batch or background mode)

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".

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

EASI>RUN THSNPOLY