How to Transform Raster into Vector
The transformation from raster representation to vector representation is a
more complex process than the other way around (that is vector to raster),
because, besides extracting the objects contour, it is also required to create
the spatial relations among them, such as neighborhood relationship, and
pertinence between polygons, and connectivity between arcs.
The transformation process raster-vector described here is adequate only for
data from models where the objects present has an area, that is polygons.
Starting from the original image, the algorithm generates a binary image that
has only the boundaries among the objects present, as shown in the example
below:
-
The boundaries are constructed using the pixels: if the original image has (n x
n) format, where n is the number of lines and also the number of columns, the
binary image will have (2n + 1) x (2n + 1) format.
-
When transforming the image into the binary format, the nodes are also
detected.
-
Next, the object contours are extracted (vectorized) from the binary image and
smoothed to attenuate the "step effect", which is a raster representation
characteristic.
-
Finally, the polygons are built and the spatial relations (neighborhood,
polygons pertinence and arc connectivity).
Before using this function, it is required to observe the thematic image
aspect. The aspect is directly related to its homogeneity. The more homogeneous
the image, the larger the probability of a successful vectorization.
Transforming from raster to vector:
-
activate the Database (
) and the desired Project (
);
-
select, using the "Control Panel"
the IL from the Thematic
category of raster representation (image) that will have its classes
represented in the vector format;
-
click on Thematic - Raster -> Vector...
in the main menu;
-
in Current Infolayer: it is informed whatever was selected in the
"Control Panel";
-
click on Yes in the Arc Smoothing button so the smoothing
process will be executed, or click on No
if the raster borders should be considered in the vector format;
-
select the Conversion Type (Total or Only Arcs). If Total
is selected a topology will be created (line adjustment and polygonalization),
and if Only Arcs
is selected only the lines file will be created;
-
click on Apply to execute the
transformation.
NOTE: Check, using the "Control Panel"
, that the information layer will have a vector representation (points, lines
and polygon classes).
See
about vector representations and raster in the SPRING
See also:
Vector-Raster Transformation
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