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	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
DBIB	Integer	Input bitmap segment	0 - 1
DBOC	Integer	Output raster channel	0 - 1
FLDNME	String	Attribute field name	0 - 64
SURMODEL	String	Surface model	0 - 25	Default: Weighted Average
SAZANGL	Float	Solar zenith and azimuth angles (deg)	0 - 2	Default: 45,90
IRADIUS	Float	Inner radius (m)	0 - 1	0 - Default: 0
ORADIUS *	Float	Outer radius (m)	1 - 1	0 -
DECAYRATE	Float	Decay rate	0 - 1	0 - 1 Default: 0.5
MAXNEIGH	Integer	Maximum number of neighbors	0 - 1	1 - Default: 10
PIXRES	Float	Output pixel resolution (m)	0 - 2
DATATYPE	String	Output raster data type	0 - 3	8U \| 16U \| 16S \| 32R Default: 32R
NODATVAL	Float	No Data value	0 - 1	Default: 0.0
REPORT	String	Report mode	0 - 192	Quick links
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILI

Specifies the PCIDSK file that contains the input point segment.

If the projection of the point segment is different from the projection of the output raster, each point will be reprojected to the raster projection before the calculation is performed.

FILO

Specifies the name of the PCIDSK image file to receive the raster channel from the point segment. If the output file is not specified, it will be assumed to be the same as the input file. If the specified output file exists, its projection must be the same as that of the input file.

If FILO is specified but does not already exist, a new PCIDSK file will be created. By default, the georeferencing information from FILI will be copied to the new FILO. If a specified pixel X/Y resolution is given that is different from FILI, the extents of FILO will be different.

DBVS

Specifies the vector segment that contains the points to convert.

DBIB

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.

The bitmap also defines the georeferencing of the output raster channel, including the projection, geographic extents, and resolution of the resulting output channel.

DBOC

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.

FLDNME

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

SURMODEL

Specifies the function to use to generate the output raster.

POTMAPSUR generates the following seven surface models:

Weighted Average (default)
Slope %
Slope (deg)
Aspect (deg)
X-Derivative
Y-Derivative
Incidence Angle
Sum

See the Details section for more information.

SAZANGL

If the selected surface model (SURMODEL) 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.

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.

IRADIUS

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.

ORADIUS

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.

DECAYRATE

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

This parameter can be specified as follows:

a value of 1 represents equal distance weighting, meaning that a decay rate is not applied to the distance weighting.
a value of 0.5 represents a linear decay
a value greater than 0 and less than 0.5 represents an exponential decay which amplifies local variations
a value greater than 0.5 and less than 1 represents an inverse exponential decay

MAXNEIGH

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.

PIXRES

This parameter applies only when a new output file is created; it allows you to specify a pixel resolution or size (in meters) for the output file. By default, the pixel size is taken from the georeferencing segment of the input file. The pixel size determines the number of pixels and lines in the output file. Decreasing the pixel size results in a larger output file and increased computation time.

DATATYPE

Specifies the data type for the output image channel.

Valid data types are:

8U: pixels are stored as 8-bit unsigned integer integer values
16S: pixels are stored as 16-bit signed integer values
16U: pixels are stored as 16-bit unsigned integer values
32R: pixels are stored as 32-bit real values; this is the default value

Note: If the specified output channel already exists, the data type from that output channel will be used instead of the one specified here.

NODATVAL

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:

TERM: generates a report on the terminal (default)
DISK: generates a report on file "IMPRPT.LST"
OFF: turns off report generation
<filename>: appends a report to the specified file

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

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)

where:

i = inner radius
o = outer radius
s = sampling radius
b = decay rate
b'= b if b <= 0.5, else b' = 1 - b

If Decay Rate > 0.5, then b' = 1 - Decay Rate

Else b' = Decay Rate

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.

Example

The point layer in segment 32 from "irvine.pix" is converted to a raster layer in a new file named "oirvine.pix". The output raster type is of type 32R, and the total sampling radius used is 150m, with a pixel resolution of 30. The surface model used in the calculation is the Weighted Average and the raster is generated with the field name PixelValue.

EASI>fili	=	"irvine.pix"
EASI>filo	=	"oirvine.pix"	! will be created if it does not exist
EASI>dbvs	=	32	! vector segment containing points
EASI>dbib	=	
EASI>dboc	=	1	! output raster channel 
EASI>fldnme	=	"PixelValue"	! use field name PixelValue to generate raster
EASI>surmodel	=		! default, 'Weighted Average'
EASI>sazangl	=		! default, 45,90
EASI>iradius	=		! default, 0
EASI>oradius	=	150	! outer radius length 150
EASI>decayrate	=		! default, 0.5
EASI>maxneigh	=		! default, 10
EASI>pixres	=	30,30	! output pixel resolution 30x30
EASI>datatype	= "32R"	! output channel type
EASI>nodatval	=		! default, 0.0

EASI>RUN POTMAPSUR

Environments	PYTHON :: EASI :: MODELER
Quick links	Description :: Parameters :: Parameter descriptions :: Details :: Example