AREAPROB

Description

AREAPROB converts a point data layer to a raster representative of an index of attractiveness asserted by a user-specified point.

Parameters

areaprob(fili, filo, dbvs, dbgeo, dbib, dboc, shape, fldnme, exponen, pixres)

Name	Type	Caption	Length	Value range
FILI *	str	Input file name	1 -
FILO	str	Output file name	0 -
DBVS *	List[int]	Input point layer	1 - 1
DBGEO	List[int]	Georeference segment or layer	0 - 1
DBIB	List[int]	Input bitmap segment or layer	0 - 1
DBOC	List[int]	Output raster channel or layer	0 - 1
SHAPE *	List[int]	Shape ID	1 - 1	1 -
FLDNME	str	Attribute field name	0 - 64	Default: ATTRIBUTE
EXPONEN	List[float]	Exponent	0 - 1	0 - Default: 2.0
PIXRES	List[float]	Pixel Resolution	0 - 2	0.0 -

* Required parameter

Parameter descriptions

FILI

Specifies the name of the file that contains the input point layer, georeference segment, and bitmap mask segment.

FILO

Specifies the name of the image file that receives the raster layer derived from the point layer. If a file name is not specified, the file name will be the same as FILI. If the file name specified for FILO exists, its projection must be the same as FILI.

If the file name specified for FILO does not exist, a new file is created. By default, the georeferencing information from FILI is copied to the new FILO. If a specified pixel x/y resolution is given and is different from that of FILI, the extents of FILO will be different.

DBVS

Specifies the input vector segment that contains the point layer to be converted to a raster layer.

DBGEO

Specifies the georeference segments that apply to the projection.

DBGEO contains the geoereferencing of the resulting raster layer and specifies the projection, geographic extents, and size (pixels/lines) of the resulting raster layer. The georeferencing can also be set from the bitmap input layer if it is specified. If this parameter and the bitmap layer are not used, the projection of the raster layer will be the same as that of the point layer. The geographic extents of the raster layer are determined by the extents of point layer and the pixel size parameters.

DBIB

Specifies the bitmap segment to sample data from the input image data.

A bitmap layer restricts the region when generating the weighted average. The results are gerenated inside the bitmap layer (value 1), and pixels falling outside the bitmap (value 0) are given a "No Data" value. The bitmap layer, if used, also defines the georeferencing of the output raster.

DBOC

Specifies the output raster channel that receives the raster layer derived from the point layer.

The georeferencing will either be determined from the georeferencing information, the bitmap layer, or calculated using the point layer extents and the pixel X/Y size.

If FILO is an existing file, DBOC must be specified.

SHAPE

Specifies the Shape ID of the point used in the calculation.

FLDNME

The input point data layer must contain a column that assigns a value to each point as an indication of its importance or its intended contribution to the final output. This is referred to as a weight. The higher the weight value, the greater the influence exerted. The following values are supported:

ATTRIBUTE (default): Uses the field called ATTRIBUTE. If ATTRIBUTE does not exist, uses the Shape ID.
Z-COORD: Uses the z-coordinate of vertices
Other numeric data fields

EXPONEN

Controls the effect of the distance decay. The higher the value, the greater the effect of the distance decay. If this parameter is not specified, this parameter is set to 2.0.

PIXRES

This parameter must be specified when DBGEO and DBIB are not specified. You can specify a pixel resolution or size (in meters) for the output file. By default, the pixel size is the same as the input file. The pixel size determines the number of pixels and lines in the output file; therefore, decreasing the pixel size results in a larger output file and increased computation time.

Valid values: x > 0.0, y > 0.0

For example:

PIXRES=400.0, 400.0 | Use a pixel size of 400m x 400m

Details

The attractiveness of a point in a gravity model is inversely proportional to distance and is directly related to the perceived attractiveness of the point itself. The point data must include weight values representing the attractiveness of each point. A weight is a numeric value assigned to each point as an indication of its importance or its intended contribution to the final output. You must also specify a distance-decay factor that calculates the diminishing attractiveness with the increasing distance. The greater the distance to the point, the less attractive the point becomes.

Using this information, AREAPROB generates areas that indicate the probability of any location within that area being attracted to the specified point. The output values are expressed as a percentage, with 0 indicating no attractiveness and 100 indicating maximum attractiveness.

The probability function is based on Reilly's improvements on the Huff model.

Example

The following example demonstrates the use of AREAPROB in generating a raster channel that is converted from a point layer.

from pci.areaprob import areaprob

fili = "irvine.pix" # set the input file
filo = "output.pix" # the name of the created output file
dbvs = [30] # point layer segment
dbgeo = [1] # geoereference segment
dbib = [10] # bitmap mask segment
dboc = [] 
shape = [3] # Shape Id
fldnme = "ATTRIBUTE" # field name
exponen = [1.0] # exponent value
pixres = [] 
areaprob( fili, filo, dbvs, dbgeo, dbib, dboc, shape, fldnme, exponen, pixres )

References

Ken Jones and Jim Simmons, Location, Location, Location: Analyzing the Retail Environment (Methuen, Toronto, 1987), pp 114-116, 263-269.

Avijit Ghosh and Sara L. McLafferty, Location Strategies for Retail and Service Firms (Lexington Books, Toronto, 1987)

Environments	PYTHON :: EASI :: MODELER
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