Changes between Version 8 and Version 9 of oid/WorkLog/08-09-22

Timestamp:

Sep 22, 2008, 10:27:33 PM (16 years ago)

Author:

jazz

Comment:

--

oid/WorkLog/08-09-22

@@ -125 +125 @@
 // - zoomlevels 型態為數字, 代表有幾種比例尺, 像這裡的比例尺是 0-9 總共 10 種
                                           new GMercatorProjection(10), "Visible" );
+}}}
+ * 繼續解析 [http://alderaan.arc.nasa.gov/maps/nasamaps.js nasamaps.js] (PART 2)
+ * 從這一個範例，我們可以學習到 JavaScript 的多型繼承該怎麼作!!
+{{{
+#!java
+// 首先定義自訂投影座標函數 PolarStereographicProjection 有兩個參數 zoomelevels 跟 type
+// 其中 zoomlevels 跟 GMercatorProjection 一樣，代表分幾種比例尺
+function PolarStereographicProjection( zoomlevels, type ) {
+  var me = this;
+  me.zoomlevels = zoomlevels;
+  me.zvector = type;
+}
 
+// 宣告 PolarStereographicProjection 實作 interface GProjection 回傳 GPoint
+PolarStereographicProjection.prototype = new GProjection();
+
+// 重新實作 interface GProjection 的 fromLatLngToPixel(latlng,  zoom)
+PolarStereographicProjection.prototype.fromLatLngToPixel = function(latlng, zoom) {
+  var lat = Math.PI/180 * latlng.lat();
+  var lon = Math.PI/180 * latlng.lng();
+  var s1 = Math.cos(lat)/(1.0 + this.zvector * Math.sin(lat));
+  var s2 = 256 / 2 * Math.pow(2,zoom);
+  var x = ( Math.sin(lon) * s1 + 1 ) * s2;
+  var y = ( this.zvector * Math.cos(lon) * s1 + 1 ) * s2;
+  return new GPoint(x,y);
+};
+
+// 重新實作 interface GProjection 的 fromPixelToLatLng(pixel,  zoom,  unbounded?) 回傳 GLatLng
+PolarStereographicProjection.prototype.fromPixelToLatLng = function(pixel, zoom, unbounded) {
+  var s2 = 256 / 2 * Math.pow(2,zoom);
+  var x = pixel.x / s2 - 1;
+  var y = pixel.y / s2 - 1;
+  if ( x == 0 && y == 0 ) return new GLatLng(90,0);
+  var z = this.zvector * Math.min( 2.0 / ( x*x + y*y + 1 ) - 1.0, 1.0 );
+  var lon = 180/Math.PI * Math.atan2( x, this.zvector * y );
+  var lat = 180/Math.PI * Math.asin( z );
+  return new GLatLng(lat,lon);
+};
+
+// 重新實作 interface GProjection 的 tileCheckRange(tile,  zoom,  tilesize) 回傳 Boolean
+PolarStereographicProjection.prototype.tileCheckRange = function(tile, zoom, tilesize) {
+  if( zoom > this.zoomlevels ) return false;
+  else return true;
+};
+
+// 重新實作 interface GProjection 的 getWrapWidth(zoom) 回傳 Number (比例尺的數字)
+PolarStereographicProjection.prototype.getWrapWidth = function(zoom) {
+  // Is there a better cross-platform way to represent Infinity here?
+  return 1E+100 * Math.pow(2,zoom);
+};
 }}}