IDINT

Description

Generates a raster image by interpolating image values between specified pixel locations using the Simple Inverse Distance or Weighted Inverse Distance algorithm.

Parameters

Name	Type	Length	Value range
Input: Data Values: Input vector segment *	Vector port	1 - 48
Output: Interpolation Image: Output image channel *	Raster port	1 - 1
Pixel X Size	Real	0 - 1024	0.0 - Default: 30.0
Pixel Y Size	Real	0 - 1024	0.0 - Default: 30.0
Field Name	String	0 - 1	ATTRIBUTE, ZCOORD Default: ATTRIBUTE
Power of Exponentiation	Integer	0 - 1	1 - 4 Default: 2
Minimum Number of Points	Integer	0 - 1	1 - 8 Default: 3
Starting Search Radius	Float	0 - 1	0.0 -
Maximum Search Radius	Float	0 - 1	0.0 - Default: 1500.0
Default Empty Value	Float	0 - 1
Method	String	0 - 1	SIMPLE | WEIGHT Default: SIMPLE

* Required parameter

Parameter descriptions

Input: Data Values: Input vector segment

Specifies the vector segment from which the attribute value or the z-coordinate will be used as the basis for interpolation.

Output: Interpolation Image: Output image channel

Specifies the output channels to receive the output interpolation image.

Pixel X Size

Specifies the X (horizontal) pixel size, in meters, of the output image. The specified X and Y pixel sizes determine the resolution of the output file. A smaller pixel size results in a larger output file and increases computation time. The default value is 30.0.

Pixel Y Size

Specifies the Y (vertical) pixel size, in meters, of the output image. The specified X and Y pixel sizes determine the resolution of the output file. A smaller pixel size results in a larger output file and increases computation time. The default value is 30.0.

Field Name

Specifies the name of the attribute field containing the elevation value.

If this parameter is not specified, it defaults to "ATTRIBUTE". If the value is specified as "ZCOORD", the actual z-coordinates of the vectors are used.

Values are not case-sensitive, and the entire name need not be specified. If more than one match is found, the first name is used.

Power of Exponentiation

Specifies a power of exponentiation. This value applies only for the Simple Inverse Distance interpolation algorithm. Valid Values are 1, 2, 3, and 4; the default value is 2.

Minimum Number of Points

Specifies the minimum number of points to search for in the given radius.

Starting Search Radius

Specifies a starting value for the search radius. The magnitude must be specified in vecunit coordinates. The dedault value is 0.125*MAXRD (Maximum Search Radius).

Maximum Search Radius

Specifies a maximum value for the search radius. The magnitude must be in vecunit coordinates.

Default Empty Value

Specifies a default empty value to assign to areas containing insufficient data to include in processing.

Method

Specifies the type of Inverse Distance algorithm to use.

Details

IDINT reads the gray-level values for an arbitrary number of pixel locations to generate a raster image based upon interpolation between the specified gray levels. It adopts the Simple Inverse Distance Simple or the Weighted Interpolation algorithm.

The gray-level values are read from a vector segment in the specified input file.

The STARTRD (Starting Search Radius) parameter specifies the size of the starting radius, which defines the beginning of the area to search for interpolation points around gridding points. The MAXRD (Maximum Search Radius) parameter specifies the maximum size of the search radius.

The MINPNT (Minimum Number of Points) parameter specifies the minimum number of interpolation points to satisfy the search requirement. If the requirement is not met and the minimum number of points are not found, the area contains insufficient data and the empty value (EMPTYVL) will be assigned to this area.

If the specified algorithm is Simple Inverse Distance, the power of exponentiation (EXPONEN) can be used. The default value is 2; higher powers of exponentiation may provide better results, but will considerably slow down processing time.

Algorithm

IDINT implements the Inverse Distance Interpolation algorithm using weighted average method. This is used primarily as a fast technique for interpolating scattered data. It produces a surface that drops inversely with the power of the distance to the next point. The tangent surface at the control points is a horizontal plane. This produces a surface which is similar to that of the tent pole being pushed up through a membrane.

Both methods are taken from the following paper:

Denis D. Weber and Evan J. Englund, 1994 Evaluation and Comparison of Spatial Interpolators II, Mathematical Geology, Vol. 26, No. 5

Simple Inverse Distance

This method is based on weights that are inversely proportional to the power of the distance from the center(Xe) of the search radius (Rs).

The general formula for simple inverse distance is:

For a point Xe = (xe,ye), the estimated value Ze is given by:

Ze = SUM[i=1,n] Z(i) * W(R(i))

The weight function W(i) at X(i) is given by:

 W(i) = TO_POWER_P (INVERSE_DISTANCE(R(i)))
        ___________________________________________
        SUM[i=1,n] TO_POWER_P (INVERSE_DISTANCE(Ri))

Weighted Inverse Distance

This method is based on weights that are proportional to the square of the distance from the center(Xe) of the search radius (Rs).

The general formula for weighted inverse distance is as follows.

For a point Xe = (xe,ye), estimated value Ze is given by:

Ze = SUM[i=1,n] Z(i) * W(R(i))

The weight function W(i) at X(i) is given by:

 W(i) = SQUARE (Norm(R(i))
        ____________________________
        SUM[i=1,n] SQUARE (Norm(R(i))

References

Denis D. Weber and Evan J. Englund, 1994 Evaluation and Comparison of Spatial Interpolators II, Mathematical Geology, Vol. 26, No. 5