57161a94be
git-svn-id: http://svn.openlayers.org/trunk/openlayers@1383 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
134 lines
5.0 KiB
JavaScript
134 lines
5.0 KiB
JavaScript
/* Copyright (c) 2006 MetaCarta, Inc., published under the BSD license.
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* See http://svn.openlayers.org/trunk/openlayers/license.txt for the full
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* text of the license. */
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/**
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* Some Layers will already have established zoom levels (like google
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* or ve). Instead of trying to determine them and populate a resolutions[]
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* Array with those values, we will hijack the resolution functionality
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* here.
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*
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* When you subclass FixedZoomLevels:
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*
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* The initResolutions() call gets nullified, meaning no resolutions[] array
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* is set up. Which would be a big problem getResolution() in Layer, since
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* it merely takes map.zoom and indexes into resolutions[]... but....
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*
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* The getResolution() call is also overridden. Instead of using the
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* resolutions[] array, we simply calculate the current resolution based
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* on the current extent and the current map size. But how will we be able
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* to calculate the current extent without knowing the resolution...?
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*
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* The getExtent() function is also overridden. Instead of calculating extent
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* based on the center point and the current resolution, we instead
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* calculate the extent by getting the lonlats at the top-left and
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* bottom-right by using the getLonLatFromViewPortPx() translation function,
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* taken from the pixel locations (0,0) and the size of the map. But how
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* will we be able to do lonlat-px translation without resolution....?
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*
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* The getZoomForResolution() method is overridden. Instead of indexing into
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* the resolutions[] array, we call OpenLayers.Layer.getExent(), passing in
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* the desired resolution. With this extent, we then call getZoomForExtent()
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*
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*
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* Whenever you implement a layer using OpenLayers.Layer.FixedZoomLevels,
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* it is your responsibility to provide the following three functions:
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*
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* - getLonLatFromViewPortPx()
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* - getViewPortPxFromLonLat()
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* - getZoomForExtent()
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*
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* ...those three functions should generally be provided by any reasonable
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* API that you might be working from.
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*
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* @class
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*/
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OpenLayers.Layer.FixedZoomLevels = Class.create();
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OpenLayers.Layer.FixedZoomLevels.prototype = {
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/********************************************************/
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/* */
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/* Baselayer Functions */
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/* */
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/* The following functions must all be implemented */
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/* by all base layers */
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/* */
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/********************************************************/
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/**
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* @constructor
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*/
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initialize: function() {
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//this class is only just to add the following functions...
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// nothing to actually do here... but it is probably a good
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// idea to have layers that use these functions call this
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// inititalize() anyways, in case at some point we decide we
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// do want to put some functionality or state in here.
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},
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initResolutions: function() {
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// resolutions are set automatically in the black-box. this is the
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// definition of a fixed-zoom-levels layer
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},
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/**
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* @returns Degrees per Pixel
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* @type float
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*/
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getResolution: function() {
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var viewSize = this.map.getSize();
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var extent = this.getExtent();
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return Math.max( extent.getWidth() / viewSize.w,
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extent.getHeight() / viewSize.h );
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},
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/** Calculates using px-> lonlat translation functions on tl and br
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* corners of viewport
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*
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* @returns A Bounds object which represents the lon/lat bounds of the
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* current viewPort.
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* @type OpenLayers.Bounds
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*/
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getExtent: function () {
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var extent = null;
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var size = this.map.getSize();
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var tlPx = new OpenLayers.Pixel(0,0);
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var tlLL = this.getLonLatFromViewPortPx(tlPx);
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var brPx = new OpenLayers.Pixel(size.w, size.h);
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var brLL = this.getLonLatFromViewPortPx(brPx);
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if ((tlLL != null) && (brLL != null)) {
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extent = new OpenLayers.Bounds(tlLL.lon,
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brLL.lat,
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brLL.lon,
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tlLL.lat);
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}
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return extent;
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},
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/**
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* @param {float} resolution
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*
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* @returns A suitable zoom level for the specified resolution.
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* If no baselayer is set, returns null.
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* @type int
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*/
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getZoomForResolution: function(resolution) {
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var extent = OpenLayers.Layer.prototype.getExtent.apply(this,
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[resolution]);
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return this.getZoomForExtent(extent);
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},
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/** @final @type String */
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CLASS_NAME: "FixedZoomLevels.js"
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};
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