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Improve reprojection performance

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Utilize the numerical shifting during reprojection to easily reduce
complexity of the linear system that needs to be solved.
This commit is contained in:
Petr Sloup
2015-07-09 18:19:10 +02:00
parent 8ab197eba6
commit 30cd0aa584
1 changed files with 8 additions and 11 deletions
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19
src/ol/reproj/reproj.js
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@@ -161,9 +161,8 @@ ol.reproj.renderTriangles = function(context,
}
// Shift all the source points to improve numerical stability
// of all the subsequent calculations.
// The [x0, y0] is used here, because it should achieve reasonable results
// but any values could actually be chosen.
// of all the subsequent calculations. The [x0, y0] is used here.
// This is also used to simplify the linear system.
var srcNumericalShiftX = x0, srcNumericalShiftY = y0;
x0 = 0;
y0 = 0;
@@ -173,20 +172,18 @@ ol.reproj.renderTriangles = function(context,
y2 -= srcNumericalShiftY;
var augmentedMatrix = [
[x0, y0, 1, 0, 0, 0, u0 / targetResolution],
[x1, y1, 1, 0, 0, 0, u1 / targetResolution],
[x2, y2, 1, 0, 0, 0, u2 / targetResolution],
[0, 0, 0, x0, y0, 1, v0 / targetResolution],
[0, 0, 0, x1, y1, 1, v1 / targetResolution],
[0, 0, 0, x2, y2, 1, v2 / targetResolution]
[x1, y1, 0, 0, (u1 - u0) / targetResolution],
[x2, y2, 0, 0, (u2 - u0) / targetResolution],
[0, 0, x1, y1, (v1 - v0) / targetResolution],
[0, 0, x2, y2, (v2 - v0) / targetResolution]
];
var coefs = ol.math.solveLinearSystem(augmentedMatrix);
if (goog.isNull(coefs)) {
return;
}
context.setTransform(coefs[0], coefs[3], coefs[1],
coefs[4], coefs[2], coefs[5]);
context.setTransform(coefs[0], coefs[2], coefs[1], coefs[3],
u0 / targetResolution, v0 / targetResolution);
var pixelSize = sourceResolution;
var centroid = [(x0 + x1 + x2) / 3, (y0 + y1 + y2) / 3];