GRDPNT

Description

Given a set of points stored in a vector layer, generates a raster image where each gray level corresponds to the attribute value of the closest point.

Parameters

Name	Type	Length	Value range
Input: Input vector segment *	Vector port	1 - 1
Output: Output raster channel *	Raster port	1 - 1
Field Name	String	0 - 1	Default: ATTRIBUTE
Output Raster Type	Text	0 - 1024	8U | 16S | 16U | 32R Default: 32R

* Required parameter

Parameter descriptions

Input: Input vector segment

Specifies the vector segment that contains point data. The vector segment may contain both point and line information; however, for the purposes of this function, only the point data and its associated attribute values are used.

Output: Output raster channel

Specifies the output image channel to receive the rasterized image.

Field Name

Specifies the field name that contains the elevation values.

If this parameter is specified as ZCOORD, the actual z-coordinates of the vectors are used. Field names are not case-sensitive, and they do not need to be specified in complete form. If more than one match exists, the first name is used.

The Field Name (FLDNME) parameter is required only for vector layers that contain 3-D points or contours. For 3-D lines, the z-coordinates are automatically used. For 2-D layers, the elevation values are not specified.

The same name applies to all contour and 3-D point segments specified in the input vectors (DBVS) parameter. The segments that do not satisfy this requirement can be converted to the required format using ZVALTRNS.

If a field name other than ZCOORD is specified but is not found, VDEMINT attempts to use the z-coordinates of each vertex or point; this may, however, lead to unexpected results.

Output Raster Type

Specifies the image data type of the output raster channel.

Details

GRDPNT uses as input the point data structures within the specified vector segment (DBVS) of the input file. An output channel (DBOC) is created in which the area of any given region represents all pixels that are closer to the attribute location defining the region than to any other attribute location specified by DBVS.

If an attribute value is out of range for the output channel data type, its value is truncated to the minimum or maximum allowable value. GRDPNT tallies the number of attributes requiring truncation measures and reports this information. If all attributes were truncated, it is likely that the wrong output channel was specified. Run CDL to check the data type for the output channel (8-bit, 16-bit signed or unsigned, or 32-bit real) and run VECREP to verify that the attribute values are within the range for the output channel data type. If only a few attributes were truncated, they too can be checked as outlined; however, these are more likely to be the result of digitizing errors or special cases.

If the units for storing vector data are not "PIXEL", but are "UTM" or any other type, the image file must be georeferenced using GEOSET prior to running GRDPNT. The georeferencing units must be the same as were used in collecting the vector data.

Vector segments can be created using RAS2PNT, with the polygon information option set to "POINT" or "BOTH", using a thematic image as input.

Each vector may contain more than one attribute field. The FLDNME (Field Name) parameter is used to select the attribute field to use.