VLM

Description

Calculates the volume between the surface of an elevation image and a specified elevation base, under a user-specified bitmap mask.

Parameters

Name	Type	Length	Value range
Input: Input raster channel *	Raster port	1 - 1
Mask: Input bitmap mask segment *	Bitmap port	1 - 1
Elevation Base for Volume Calculation	Float	0 - 1	Default: 0.0
Pixel X Size	Float	0 - 1
Pixel Y Size	Float	0 - 1
Elevation Step Size	Float	0 - 1	Default: 1.0
Sum of Abs. Vol. under Bitmap Mask *	Float	4 - 4
Sum of Net Vol. under Bitmap Mask *	Float	4 - 4
Sum of + Vol. under Bitmap Mask *	Float	4 - 4
Sum of - Vol. under Bitmap Mask *	Float	4 - 4
Report	String	0 - 192	See parameter description

* Required parameter

Parameter descriptions

Input: Input raster channel

Specifies the input channel that contains the elevation data.

Mask: Input bitmap mask segment

Specifies the bitmap segment (Type 101) that defines the area for which the volume will be calculated.

Elevation Base for Volume Calculation

Specifies the base elevation for volume measurements. Volume is calculated between the surface of the elevation image and this elevation level.

Pixel X Size

Specifies, in meters, the X (horizontal) dimension of one pixel on the ground.

Correct calculation of the volume depends on proper specification of this value.

Pixel Y Size

Specifies, in meters, the Y (vertical) dimension of one pixel on the ground.

Correct calculation of the volume depends on proper specification of this value.

Elevation Step Size

Specifies, in meters, the elevation corresponding to one gray level.

A change of one gray level in the elevation image corresponds to a change in elevation of ELSZ (Elevation step) meters. Correct calculation of the real and projected areas depends on proper specification of this value.

Sum of Abs. Vol. under Bitmap Mask

Sum of Net Vol. under Bitmap Mask

Sum of + Vol. under Bitmap Mask

Sum of - Vol. under Bitmap Mask

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

VLM uses an elevation channel stored on the database file to calculate the volume between the surface of a bitmap-defined region and a user-specified base elevation.

The volume between the surface defined by the elevation data and the specified elevation base is calculated under the bitmap mask. Note that volume can either be positive (elevation is above base elevation) or negative (elevation is below base elevation).

The total absolute volume (sum of absolute values of positive and negative volumes), in cubic kilometers, is written to the first IMSTAT array element (Sum of Abs. Vol.). The total net volume (difference between positive and negative volumes), in cubic kilometers, is written to the second IMSTAT array element (Sum of Net Vol.). The positive volume is written to the third IMSTAT array element (Sum of + Vol.), and the absolute value of the negative volume is written to the fourth IMSTAT array element (Sum of - Vol.). The calculation results are also written to the report device.

Correct calculation of the volume is dependent on the proper specification of the elevation step size and the ground pixel size. If defaulted, the elevation step size is set equal to 1.