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Estimate point resolution for Proj4js projections

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This commit is contained in:
Tom Payne
2013-03-03 17:19:18 +01:00
parent 343768df6a
commit a8760108d4
2 changed files with 70 additions and 0 deletions
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40
src/ol/projection.js
View File

@@ -8,6 +8,7 @@ goog.require('goog.object');
goog.require('ol.Coordinate');
goog.require('ol.Extent');
goog.require('ol.TransformFunction');
goog.require('ol.sphere.NORMAL');
/**
@@ -129,10 +130,49 @@ ol.Proj4jsProjection_ = function(code, proj4jsProj) {
*/
this.proj4jsProj_ = proj4jsProj;
/**
* @private
* @type {?ol.TransformFunction}
*/
this.toEPSG4326_ = null;
};
goog.inherits(ol.Proj4jsProjection_, ol.Projection);
/**
* @inheritDoc
*/
ol.Proj4jsProjection_.prototype.getPointResolution =
function(resolution, point) {
if (this.getUnits() == ol.ProjectionUnits.DEGREES) {
return resolution;
} else {
// Estimate point resolution by transforming the center pixel to EPSG:4326,
// measuring its width and height on the normal sphere, and taking the
// average of the width and height.
if (goog.isNull(this.toEPSG4326_)) {
this.toEPSG4326_ = ol.projection.getTransform(
this, ol.projection.getProj4jsProjectionFromCode_('EPSG:4326'));
}
var vertices = [
point.x - resolution / 2, point.y,
point.x + resolution / 2, point.y,
point.x, point.y - resolution / 2,
point.x, point.y + resolution / 2
];
vertices = this.toEPSG4326_(vertices, vertices, 2);
var width = ol.sphere.NORMAL.haversineDistance(
new ol.Coordinate(vertices[0], vertices[1]),
new ol.Coordinate(vertices[2], vertices[3]));
var height = ol.sphere.NORMAL.haversineDistance(
new ol.Coordinate(vertices[4], vertices[5]),
new ol.Coordinate(vertices[6], vertices[7]));
return (width + height) / 2;
}
};
/**
* @return {Proj4js.Proj} Proj4js projection.
*/

30
test/spec/ol/projection.test.js
View File

@@ -144,6 +144,36 @@ describe('ol.projection', function() {
expect(point.y).toRoughlyEqual(200146.976, 1);
});
it('numerically estimates point scale at the equator', function() {
var googleProjection = ol.projection.getFromCode('GOOGLE');
expect(googleProjection.getPointResolution(1, new ol.Coordinate(0, 0))).
toRoughlyEqual(1, 1e-1);
});
it('numerically estimates point scale at various latitudes', function() {
var epsg3857Projection = ol.projection.getFromCode('EPSG:3857');
var googleProjection = ol.projection.getFromCode('GOOGLE');
var point, y;
for (y = -20; y <= 20; ++y) {
point = new ol.Coordinate(0, 1000000 * y);
expect(googleProjection.getPointResolution(1, point)).toRoughlyEqual(
epsg3857Projection.getPointResolution(1, point), 1e-1);
}
});
it('numerically estimates point scale at various points', function() {
var epsg3857Projection = ol.projection.getFromCode('EPSG:3857');
var googleProjection = ol.projection.getFromCode('GOOGLE');
var point, x, y;
for (x = -20; x <= 20; ++x) {
for (y = -20; y <= 20; ++y) {
point = new ol.Coordinate(1000000 * x, 1000000 * y);
expect(googleProjection.getPointResolution(1, point)).toRoughlyEqual(
epsg3857Projection.getPointResolution(1, point), 1e-1);
}
}
});
});
describe('ol.projection.getTransform()', function() {