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Index |
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| Raster Files | A-Z | Attribute Value Files |
primarily IDRISI is raster-based, but vectors can be used to get data from other sources into IDRISI. Further they serve as overlays for better visual orientation. We can digitize vector-polygons onscreen during the process of supervised image classification to define our training areas, and we will tell IDRISI where to put texts in our maps through vector-points.
See how IDRISI vector-files are structured:
Id n x1 y1 x2 y2 x3 y3 ...... xn yn Id n x1 y1 x2 y2 ...... ...... 0 0
2 columns, 1st line holds an identifier (integer or real) plus the number of
coordinates following (in case of point-files = 1). As many lines as specified
before define the vertex-coordinates. Each vector-file has to end with
0 0 (zero zero).
Polygon-vectors are cycled in that the last X/Y-pair equals the first one for each
single polygon.
Let us take height-data (eg. from a GPS) as an example for a point-vector file:
1211 1 212328.0 424876.0 1250 1 212400.0 425090.0 1283 1 213222.5 426112.5 ...... 1423 1 215089.2 428987.6 1423 1 215234.0 429876.7 0 0
See? Identifiers need not be unequivocal. In this case they mean the heights of the points.
Vector Documentation Files
The vector-file too is a 'dumb thing', that has to be told about its nature, so
every IDRISI vector-file (*.VEC) comes with a vector documentation file (*.DVC).
The module DOCUMENT again helps to input the metadata:
You'll find one additional field - Object type - which can be Point, Line, Polygon or Text. Of course you can not automatically calculate the vectors resolution. It is your responsibility to put in a value if known. The remaining fields have same meanings as with raster documentation.
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Index |
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| Raster Files | A-Z | Attribute Value Files |