How to execute the Vector to Raster transformation

The Vector-Raster transformation creates a Thematic Image representation from the classes in the IL. An IL may have only a Thematic Image. If there is any change in the vectors and classes, the transformation has to be performed again.

This transformation generates an image in the raster format from data represented vectorially. There are two cases to be considered: the linear element and the polygon.

For a linear element the transformation can be performed joining the vector or linear element, to a raster matrix. This transformation identifies what raster elements are crossing a line and codes them with attributes or class values associated to the line.


Example:

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For polygonal elements, the area to be converted is initially defined (typically the rectangle involving the set of polygons) and the "pixel" size. These information define a grid which is placed over the original polygon map. A class has to be associated to each "pixel" (or an attribute value). There are several solutions for this problem. The most common consists in computing the "pixel" center and verifies inside what polygon is placed, associating to the "pixel " the class value defined for the polygon.

The figure below shows the vector-raster transformation procedure.

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The vector to raster transformation adds distortion in the data original geometry. These distortions increase with the "pixel " size and with the polygons boundary complexity. "Pixels" located at the boundary will be mapped to the closest polygon.

The smaller the cell size ("pixel "), the higher the transformed image fidelity, however, the thematic image requires more storage space.

Vector Raster Transformation:

  • activate the Database ( ) and the desired Project ( );
  • select using the "Control Panel" the IL of the Thematic category which will have its classes represented in the raster format;
  • click on Thematic - Vector -> Raster... in the main menu;
  • in the Active IL: it is informed whatever was selected in the "Control Panel";
  • in Output Image Resolution: type the Horizontal and Vertical resolution for the image that will be generated;
  • click on Apply to execute the transformation;


NOTE : An IL may have only one thematic image. If another resolution was desired, the transformation has to be executed again. The old thematic image will be changed. The image resolution has to be the best possible to represent the vector details present in the IL. This resolution is limited to the available storage space. It is suggested a maximum resolution compatible to the map precision limit, that is 0.5 mm times the map scale. For a given scale, say 1:100.000, the 50m resolution is adequate.

NOTE: Check in the "Control Panel" that the thematic information layer will have an image representation.


See about the vector and raster representation in the SPRING

See also:
Vector- Raster Transformation