VECBUF -- Create Buffer Zone Around Vector Set

Creates a graphic mask defining a buffer zone which surrounds vector data, given a user specified buffer width.

See Also: PRX, VECSEL, MAP, GRDVEC

PARAMETERS

VECBUF is controlled by the following global parameters: 

Name     Prompt                                  Count     Type
FILE     Database File Name                      1-64      Char
DBVS     Database Vector Segment                 1         Int
DBOB     Database Output Bitmap                  0-1       Int
DBOW     Database Output Window                  0-4       Int
BUFDIST  Buffer Distance (geo units)             1         Real

FILE

Specifies the name of the PCIDSK file containing the input data and receiving the output results. 

 EASI>FILE="filespec"

BUFDIST

Specifies the buffering distance around vectors in the distance units of the georeferencing segment of the PCIDSK file. If the file is not georeferenced this would be PIXELS, otherwise it is meters, feet, or decimal degrees depending on the georeferencing system of the file. 

 EASI> BUFDIST = 200            | Select 200m region around vectors.

DBVS

Specifies the vector segment containing the the vectors for which a buffer zone is to be constructed. 

 EASI> DBVS=i

DBOB

Specifies the graphic bitmap into which the vector buffer results should be written. A value of 1 (on) will be written to all bitmap pixels that are within BUFDIST of a vector feature. All other pixels will be unchanged. If no output bitmap is provided a new segment will be created, and initialized to all zero. 

 EASI> DBOB = 9         | Write to existing segment 9
or 

 EASI> DBOB =           | Create a new bitmap segment

DBOW

Specifies the window out the output mask to be computed. All other regions on the mask will remain unaffected. 

 EASI>DBOW=Xoffset,Yoffset,Xsize,Ysize
 EASI>DBOW=                     | use full file area

DETAILS

The VECBUF program is used to generate masks for buffer regions around features stored as vector data. The programs acts to burn a value of 1 into the output bitmap segment for all pixels considered to be within the buffer area of one or more vectors.

The buffer area includes all pixels within BUFDIST units of any of the vector features in the given vector segment (VECBUF). Note that all vectors are treated as points, or polylines. Closed polylines are not treated as filled polygons.

The result of the VECBUF program is a bitmap segment marking pixels within the buffer distance of the vector segment lines. This result may be burned into an image channel using the THR program. The PRX (proximity analysis) program may be used to achieve somewhat similar results with raster source data. The GRDVEC program can be used to simply burn vector data into an image channel.

The algorithm used is quite simplistic, and will produced squared, rather than rounded masks at the ends of lines. Strictly speaking this means that the proximity test is inaccurate at the end points. This effect is particularly pronounced for point features for which the resulting buffer is always a square, not a circle.

EXAMPLE

Build a mask of all regions within 150m of the hydrography vectors in segment 26. 

 EASI> file = "irvine.pix"
 EASI> bufdist = 150
 EASI> dbvs = 26
 EASI> dbob =
 EASI> dbow =
 EASI> run vecbuf
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