POTMAPSUR

Description

POTMAPSUR converts a vector point segment to a raster representative of a selected attribute, referred to as a z-value, of the points. The surface derivative models are the weighted average of z-values, slope, aspect, x and y derivatives, angle of incidence, and sum. Because it uses an averaging technique, this function does not create any new values greater than the maximum value of the input data or less than the minimum value of the input z-value.

Parameters

Name	Type	Length	Value range
InputPoints: Input vector segment*	Vector port	1 - 1
Bitmap: Input bitmap segment	Bitmap port	0 - 1
InputArea: Georeferencing segment	GEO port	0 - 1
Output: Output raster channel	Raster port	0 - 1
Attribute	String	0 - 1
Function	String	0 - 1	Default: Weighted Average
Azimuth Angle of Light Source	Float	0 - 2	0 - 359 Default: 90
Zenith Angle of Light Source	Float	0 - 2	0 - 90 Default: 45
Inner Radius	Float	0 - 1	0 - Default: 0
Outer Radius*	Float	1 - 1	0 -
Decay Rate	Float	0 - 1	0 - 1 Default: 0.5
Maximum neighbors	Integer	0 - 1	1 - Default: 10
Pixel X Size	Float	0 - 1
Pixel Y Size	Float	0 - 1
Data Type	String	0 - 1	8U | 16U | 16S | 32R Default: 32R
No Data Value	Float	0 - 1	Default: 0.0
Report	String	0 - 192	See parameter description

* Required parameter

Parameter descriptions

InputPoints: Input vector segment

Specifies the vector segment that contains the points to convert.

Bitmap: Input bitmap segment

Specifies the bitmap segment that restricts the region to process when generating the weighted average. The results will be generated inside the bitmap segment (value 1); any pixels falling outside the bitmap (value 0) will be assigned a "No Data" value.

InputArea: Georeferencing segment

Specifies the georeferencing of the output raster channel, including the projection, geographic extents, and resolution of the resulting output channel.

If this parameter is not set, the projection of the output channel will be the same as that of the input point segment. The geographic extents of the raster channel will be based on the extents of the point segment and the pixel X and Y size parameters.

Output: Output raster channel

Specifies the output raster channel to receive converted points.

If the output file already exists, this parameter must be specified and must exist. If the output file does not exist, this parameter is ignored.

Attribute

Specifies the attribute field name to use to generate the raster; for example, PixelValue.

Function

Specifies the function to use to generate the output raster.

See the Details section for more information.

Azimuth Angle of Light Source

If the selected surface model is "Incidence Angle", the solar zenith and solar azimuth angles are used to determine the direction of the light source.

The azimuth is the direction measured in degrees clockwise from North. North has an azimuth of 0 degrees; East has an azimuth of 90 degrees; South has an azimuth of 180 degrees; and West has an azimuth of 270 degrees. Enter a value from 0 to 359.

Zenith Angle of Light Source

If the selected surface model is "Incidence Angle", the solar zenith and solar azimuth angles are used to determine the direction of the light source.

The zenith is the angle, in degrees, of the ray of light with respect to the vertical. A zenith angle of 0 degrees is in line with the vertical; an angle of 90 degrees indicates dawn or dusk. Enter a value from 0 to 90.

Inner Radius

Specifies the inner radius value, in meters.

The Inner Radius plus the Outer Radius equal the total sampling radius. The total sampling radius is centered on each point in the data layer. Pixels within the distance of the inner radius will be given a weight of 1.

The Decay Rate is not applied to the area encompassed by the inner radius. Either the Inner Radius or the Outer Radius, but not both, may be zero.

Outer Radius

Specifies the outer radius value, in meters.

The Inner Radius plus the Outer Radius equal the total sampling radius. The outer radius is measured from the outer edge of the inner radius. The total sampling radius is centered on each point in the data layer.

The Decay Rate is applied only to the area encompassed by the outer radius. Either the Inner Radius or the Outer Radius, but not both, may be zero.

Decay Rate

Specifies the Decay Rate applied to the area encompassed by the outer radius.

Maximum neighbors

Specifies the maximum number of points closest to the center of the pixel and whose radii overlap the center of the pixel to be considered in calculating an output value.

When points represent statistical data values such as population or income, the number of neighboring points should be greater than when the point data represents a non-statistical and continuous nature, such as elevation.

Pixel X Size

Specifies the horizontal (X) pixel size, in meters, for the output raster layer projection.

If a georeferencing segment (InputArea) is specified, this parameter ignored.

Pixel Y Size

Specifies the vertical (Y) pixel size, in meters, for the output raster layer projection.

If a georeferencing segment (InputArea) is specified, this parameter ignored.

Data Type

Specifies the data type for the output image channel.

No Data Value

Specifies the No Data (background) value. Any output pixels that did not receive a calculated value are assigned a No Data value and are excluded from processing. This value should fall within the allowable range for the output raster type.

If this parameter is not specified, the No Data value for each channel defaults to "0.0"

Report

Specifies where to direct the generated report.

Available options are:

• LOG: generates a report on the terminal (default)
• <modulename.RPT>: appends a report to the module's RPT file
• DISK: generates a report on file "IMPRPT.LST"

Details

The weighted averaging technique used by POTMAPSUR generates a surface by applying a sampling radius to each point in the data layer. No output values are calculated for areas lying outside the sampling radius; these will be assigned a NoData value, as specified in the NODATAVAL parameter. The value of each raster pixel is calculated based on the value of each point whose sampling radius overlaps the center of the pixel. The greater the distance the pixel is from the point, the less influence the point has in determining the output pixel value. You can control the effect distance has in determining the output pixel value by changing the size of the sampling radius and the distance decay rate. You can also specify a limit for the number of points closest to the raster pixel through the Maximum Neighbors (MAXNEIGH) parameter, to reduce the number of points influencing the calculation.

Calculating the distance weighting

The potential mapping surface module calculates the effect of the distance-related weighting based on the size of the sampling radius applied to each point in the data layer and on the rate of decay applied to the sampling radius. The greater the distance from the center of the pixel to the point at the center of the sampling radius and the greater the rate of decay, the less of an influence that point has on determining the output value. You can control the effect of the distance-related weighting by specifying the size of the sampling radius and the rate of decay. Depending on the size of the inner and outer radii and on the decay rate specified, very different surfaces can be generated.

The calculation for the distance related weighting is:

If distance to data point > o, Distance Weighting = 0;
Else if distance to data point < i, Distance Weighting = 1
Else Distance Weighting = (2 x (1-b')) (-d/(b' x o)) x ((o-d)/o)

The sampling radius

You specify the size of the sampling radius for all of the points in the data layer using the Inner Radius and the Outer Radius parameters. The inner radius plus the outer radius equal the total sampling radius. The larger the sampling radius, the greater the effect of the smoothing, which reduces variations in the data. Where points are dense, a small decay rate and a low number of neighbors can still create an acceptable local sampling. Processing time increases with the size of the sampling radius and the number of neighbors to be considered.