Le 07/09/2011 00:02, Curtis Jensen a écrit :
Below is a simpler example. Here, set2 is a polygon completely
encompassed by the set1 polygon. Yet the difference function produces
a single polygon that doesn't seem to be a difference in any sense
that I can understand. How are the verticies of a polygon suppose to
be interpreted?
Using these values, I see set1 as a square and set2 as a triangle which
overlaps set1 right boundary. that is to say it is partly inside set1
and partly outside set1 (for the part with x lying between -4.2 and -4.0).
So the resulting polygon with one simply connected boundary which look
like a dented square seems fine to me. The boundary vertices I get are:
-7.2 0.10000000000000002
-4.2 0.10000000000000002
-4.2 1.0705882352941176
-5.699999999999999 1.5999999999999996
-4.2 1.9529411764705877
-4.2 3.1
-7.199999999999999 3.1000000000000005
I also tried to truncate the triangle to the right by changing the
abscissas of the last to points from -4.0 to -4.3 so the triangle lies
completely inside the square also gives a result I would consider
correct: two loops defining a square with a triangular hole.
What result do you get ?
Luc
Thanks,
Curtis
public void testdifferenceWithHole() {
Vector2D[][] vertices1 = new Vector2D[][] {
new Vector2D[] {
new Vector2D(-7.2, 3.1),
new Vector2D(-7.2, 0.1),
new Vector2D(-4.2, 0.1),
new Vector2D(-4.2, 3.1)
}
};
PolygonsSet set1 = buildSet(vertices1);
Vector2D[][] vertices2 = new Vector2D[][] {
new Vector2D[] {
new Vector2D(-5.7, 1.6),
new Vector2D(-4.0, 1.0),
new Vector2D(-4.0, 2.0)
}
};
PolygonsSet set2 = buildSet(vertices2);
PolygonsSet setDiff = (PolygonsSet) new
RegionFactory<Euclidean2D>().difference(set1.copySelf(),
set2.copySelf());
Vector2D[][] diffVerts = setDiff.getVertices();
for (int i = 0; i< diffVerts.length; i++) {
System.out.println("Verts: " + i);
Vector2D[] set = diffVerts[i];
for (Vector2D vertex : set) {
System.out.println("\t" + vertex);
}
}
}
On Fri, Aug 26, 2011 at 11:41 AM, Curtis Jensen<[email protected]> wrote:
Using math 3.0, I have two polygons with many points. One is
completely contained within the other. When I do a difference on the
two, I expected to get a polygon with a hole in it. However, I get 86
polygons, that roughly make up a polygon with a hole in it. If I
scale the points by a factor of 0.1, I get 7 polygons, and if I scale
it differently in the two directions, I get a different number of
polygons. Sometimes the resultant polygons don't seem to make a shape
resembling a polygon with a hole in it.
How should I interpret the results of the difference method? i.e. How
do I process the 86 or 7 or however many polygons so that it resembles
1 polygon with 1 hole in it?
Thanks,
Curtis
Attached are two csv files with the points in CCW order. Also
attached is a plot of the points in the two files. Below is code I
added to the org.apache.commons.math.geometry.euclidean.twod.PolygonsSetTest
class to test with (It uses the Apache Common FileUtils too)
@Test
public void testDifferenceManyPoints() throws IOException {
PolygonsSet set1 = csv2set(new File("src_ccw.csv"));
PolygonsSet set2 = csv2set(new File("inner_ccw.csv"));
PolygonsSet set = (PolygonsSet) new
RegionFactory<Euclidean2D>().difference(set1.copySelf(),
set2.copySelf());
Vector2D[][] verts = set.getVertices();
System.out.println(verts.length);
}
private PolygonsSet csv2set(File file) throws IOException {
List linesObj = FileUtils.readLines(file);
Vector2D[][] verts = new Vector2D[1][linesObj.size()];
for (int i = 0; i< linesObj.size(); i++) {
String line = (String)linesObj.get(i);
String[] tokens = line.split(",");
double x = Double.valueOf(tokens[0]);
double y = Double.valueOf(tokens[1]);
verts[0][i] = new Vector2D(x, y);
}
return buildSet(verts);
}
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