VIMAGE

Name	Type	Length	Value range
Input: Input raster channel *	Raster port	1 - 1
Mask: Area mask	Bitmap port	0 - 1
InputVec: *	Vector port	1 - 1
Output: Output vector segment *	Vector port	1 - 1
Output Column Names	String	0 -
Sampling Method	String	0 -	POINT \| MEAN \| MODE \| MEDIAN \| MIN \| MAX \| SUM \| HIST \| COUNT \| STDEV \| VAR Default: POINT
Value for Undefined Operations	Float	0 - 1024	Default: 0.0

Parameter descriptions

Input: Input raster channel

Specifies the raster image channel to be sampled.

Mask: Area mask

Optionally specifies the bitmap that defines the area to be processed within the input raster.

Only the area under the mask is written to the output. If this parameter is not specified, the entire channel is processed.

InputVec:

Specifies the vector segment that contains the points or polygons to use for sampling purposes.

Polygons may be expressed as simple closed polygons, polygons with multiple rings, or polygons stored as a topology.

Output: Output vector segment

Specifies the vector segment to receive the new column of image statistics.

Output Column Names

Specifies the names of the new columns to be added to the table in the output vector segment.

If the specified column already exists, that column's contents will be replaced, instead of adding a new field to the table.

If this parameter is not specified, a default column names will be added, based on the "Sampling Method" operation and the channel being operated on.

If this value is set and there are more than one "Sampling Method" set, one column name per "Sampling Method" must be set. Each name is delimited by a comma.

Sampling Method

Specifies the sampling methods used to compute the value of the new column, based on the input image.

Multiple sampling methods can be specified using commas.

Supported methods are:

POINT (default)
MEAN
MODE
MEDIAN
MIN
MAX
SUM
HIST
COUNT
STDEV
VAR

The sampling methods are described in the Details section.

Value for Undefined Operations

Specifies the values assigned to the output field for which an output value cannot be computed. This value will be used for vectors that fall outside the available image region, as well as to non-point structures when the sampling method is POINT, and to non-polygon structures when a polygon-based sample type is selected.

If this value is set, one value per "Sampling Method" must be specified.

Details

VIMAGE reads a single image channel (DBIC) from an input raster file. It then samples all the pixels associated with the polygon and/or point structures in an input vector segment (DBVS) in the input vector file (FILV). These pixels are then used to compute an image statistic related to that point or polygon, and the statistic is written to a new attribute field (OCOLUMN) for that vector structure.

The SAMPTYP (Sampling Method) parameter is used to define the type of statistic generated. Supported sampling methods are:

POINT: Only computes a value for point vectors (one vertex); the computed value will be the value of the image pixel in which this point falls.
MEAN: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be the arithmetic mean of the image values of all pixels inside the polygon.
MODE: Only computes a value for polygon structures. The computed value will be the mode (value with the highest occurrence count) of image values in the polygon. Floating point images are binned as if they were integers in the range of -32768 to 65536, potentially invalidating the results.
MEDIAN: Only computes a value for polygon structures. The computed value will be the median (value with half the pixels greater, and half lower) of image values in the polygon. Floating point images are binned as if they were integers in the range of -32768 to 65536, potentially invalidating the results.
MIN: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be minimum image value of all pixels inside the polygon.
MAX: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be the maximum image value of all pixels inside the polygon.
SUM: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be sum of image values in the polygon.
HISTnnn: Only computes a value for polygon structures. The computed value will be the count of pixels within the polygon that had the value "nnn", where nnn is the number appearing immediately after the keyword HIST. This is useful for getting counts of classification results within a polygon.
COUNT: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be the number of pixels falling inside the polygon.
STDEV: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be the standard deviation value of all pixels inside the polygon.
VAR: Only computes a value for polygon structures (more than two vertices, and the last vertex is the same as the first vertex). The computed value will be the variance value of all pixels inside the polygon.

Vector structures that do not match the criteria for the sampling method (must be a single vertex for POINT, or a closed polygon for the others) have a default undefined operation value (UNDEFVAL) assigned to the output attribute (OCOLUMN). This also occurs if the vector does not overlay the image, or in the case of polygons with no pixels (based on the center of the pixels) within the polygon.

Vector polygons may be expressed as simple whole polygons (closed polylines), as multi-ring polygons (via RingStart field), or as topological polygons.

The statistics for polygons are based on all pixels for which the center of the pixel falls within, or on the boundary of, the pixel. Pixel contributions are not weighted according to the amount of the pixel within the polygon.

The HIST, MODE, and MEDIAN statistics are computed based on building an in-memory histogram for floating point channels, but the histogram bins the values to integers in the range -32768 to 65536. In many cases, this means the HIST, MODE and MEDIAN results for floating point channels will be inaccurate, or even meaningless.

The VIMAGE program computes statistics by looping over all vectors and, for each appropriate vector, reads the image rectangle containing the vector for sampling purposes. This means that if several large vector polygons are being processed, the overall processing time can be very slow.

Environments	PYTHON :: EASI :: MODELER
Batch Mode	Yes
Quick links	Description :: Parameters :: Parameter descriptions :: Details :: Related

VIMAGE

Collect image point/polygon statistics

Description

Parameters

Parameter descriptions

Details