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Exploit known sense of rings to simplify area calculation

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This commit is contained in:
Tom Payne
2013-12-02 12:15:07 +01:00
parent 8852e3198c
commit 01c185ef57
2 changed files with 4 additions and 10 deletions
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12
src/ol/geom/flatgeom.js
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@@ -271,11 +271,11 @@ ol.geom.flat.linearRingArea = function(flatCoordinates, offset, end, stride) {
for (; offset < end; offset += stride) {
var x2 = flatCoordinates[offset];
var y2 = flatCoordinates[offset + 1];
twiceArea += x1 * y2 - y1 * x2;
twiceArea += y1 * x2 - x1 * y2;
x1 = x2;
y1 = y2;
}
return Math.abs(twiceArea / 2);
return twiceArea / 2;
};
@@ -383,13 +383,7 @@ ol.geom.flat.linearRingsArea = function(flatCoordinates, offset, ends, stride) {
var i, ii;
for (i = 0, ii = ends.length; i < ii; ++i) {
var end = ends[i];
var linearRingArea =
ol.geom.flat.linearRingArea(flatCoordinates, offset, end, stride);
if (i === 0) {
area += linearRingArea;
} else {
area -= linearRingArea;
}
area += ol.geom.flat.linearRingArea(flatCoordinates, offset, end, stride);
offset = end;
}
return area;

2
test/spec/ol/geom/flatgeom.test.js
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@@ -163,7 +163,7 @@ describe('ol.geom.flat', function() {
it('calculates the area with holes', function() {
var area = ol.geom.flat.linearRingsArea(
[0, 0, 0, 3, 3, 3, 3, 0, 1, 1, 1, 2, 2, 2, 2, 1], 0, [8, 16], 2);
[0, 0, 0, 3, 3, 3, 3, 0, 1, 1, 2, 1, 2, 2, 1, 2], 0, [8, 16], 2);
expect(area).to.be(8);
});