POLY2RAS

Description

POLY2RAS converts, or rasterizes, polygons in a vector layer to a raster layer.

Parameters

Name	Type	Length	Value range
Input: Input polygon layer *	Vector port	1 - 1
InputArea: Bounding area	GEO port	0 - 1
OutputRaster: Output raster layer	Raster port	0 - 1
Output type	String	0 - 1	Raster | Thematic Raster Default: Raster
Field Name	String	0 -	Default: ATTRIBUTE
Pixel X Size	Real	0 - 1	0.0 -
Pixel Y Size	Real	0 - 1	0.0 -
Use current selection (Focus only)	Boolean	0 - 1	TRUE | FALSE Default: FALSE

* Required parameter

Parameter descriptions

Input: Input polygon layer

Specifies the vector segment containing the polygons to be converted to rasters. The input vector layer can either be whole polygons or topological polygons.

InputArea: Bounding area

Specifies a georeferencing segment to be used to set the projection, geographic extents, and the size (pixels/lines) of the output raster layer. If this port is not set, the projection of the raster layer will be the same as the polygon layer. The geographic extents of the raster layer is then determined based on the extents of the polygon layer and the pixel size parameters (see Pixel X Size and Pixel Y Size).

OutputRaster: Output raster layer

Specifies the output file name to be created.

The ouptut channel's bit depth is automatically determined, depending on the values to be written to the raster.

Output type

Specifies the output raster channel or layer type.

Field Name

Specifies the name of the attribute field whose value is to be used to grid the polygons. If this parameter is specified as (z-coord), the z-coordinate of the first vertex of each vector shape is used. If the specified attribute does not exist and it is not (z-coord), the ShapeID of the vector shapes are used for gridding. This parameter is ignored when the output is a thematic raster.

The only time the field can be of type text (string) is if it is a classification field created by Object Analyst. In such a case, POLY2RAS can be used to rasterize the Object Analyst classification.

Pixel X Size

Specifies the horizontal pixel size for the raster layer. This parameter is disabled if the georeferencing is specified by the InputArea port.

Pixel Y Size

Specifies the vertical pixel size for the raster layer. This parameter is disabled if the georeferencing is specified by the InputArea port.

Use current selection (Focus only)

Allows you to restrict processing to only the selected shapes from the current view in CATALYST Professional Focus. The default value is FALSE so all shapes are processed.

Details

POLY2RAS converts polygons in a vector layer to a raster layer.

First, if the complete boundary of each polygon is specified in a single vector, the polygon scanline conversion algorithm is applied to directly grid the polygons. In order to use this algorithm, each vector in the specified vector layers must be a closed curve (or several closed rings) with at least four vertices (including a pair of duplicated vertices). The scanline conversion algorithm can process polygons with holes or even with islands within holes, as long as the entire boundaries (exterior and interior) of each polygon are given in one shape.

The output channel type is automatically determined, depending on the values to be written to raster.

POLY2RAS accepts whole polygons or topological polygons as input. The output pixel value for a polygon is derived from the vector attribute value whose name is given by the FLDNME (Field Name) parameter unless you're outputting a thematic raster. When creating thematic rasters the pixel values are determined automatically.

• If this parameter is set to (z-coord), the z-coordinate of the first vertex is used.
• If the FLDNME (Field Name) parameter is unspecified, the internal ShapeID of the vector is used for gridding.

Any raster area not covered by a polygon is filled with a background value. This background value (typically chosen as zero, if available) should be different from all other polygon gray levels.