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node_modules/proj4/lib/projections/cea.js

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+import adjust_lon from '../common/adjust_lon';
+import qsfnz from '../common/qsfnz';
+import msfnz from '../common/msfnz';
+import iqsfnz from '../common/iqsfnz';
+
+/*
+  reference:
+    "Cartographic Projection Procedures for the UNIX Environment-
+    A User's Manual" by Gerald I. Evenden,
+    USGS Open File Report 90-284and Release 4 Interim Reports (2003)
+*/
+export function init() {
+  //no-op
+  if (!this.sphere) {
+    this.k0 = msfnz(this.e, Math.sin(this.lat_ts), Math.cos(this.lat_ts));
+  }
+}
+
+/* Cylindrical Equal Area forward equations--mapping lat,long to x,y
+    ------------------------------------------------------------*/
+export function forward(p) {
+  var lon = p.x;
+  var lat = p.y;
+  var x, y;
+  /* Forward equations
+      -----------------*/
+  var dlon = adjust_lon(lon - this.long0);
+  if (this.sphere) {
+    x = this.x0 + this.a * dlon * Math.cos(this.lat_ts);
+    y = this.y0 + this.a * Math.sin(lat) / Math.cos(this.lat_ts);
+  }
+  else {
+    var qs = qsfnz(this.e, Math.sin(lat));
+    x = this.x0 + this.a * this.k0 * dlon;
+    y = this.y0 + this.a * qs * 0.5 / this.k0;
+  }
+
+  p.x = x;
+  p.y = y;
+  return p;
+}
+
+/* Cylindrical Equal Area inverse equations--mapping x,y to lat/long
+    ------------------------------------------------------------*/
+export function inverse(p) {
+  p.x -= this.x0;
+  p.y -= this.y0;
+  var lon, lat;
+
+  if (this.sphere) {
+    lon = adjust_lon(this.long0 + (p.x / this.a) / Math.cos(this.lat_ts));
+    lat = Math.asin((p.y / this.a) * Math.cos(this.lat_ts));
+  }
+  else {
+    lat = iqsfnz(this.e, 2 * p.y * this.k0 / this.a);
+    lon = adjust_lon(this.long0 + p.x / (this.a * this.k0));
+  }
+
+  p.x = lon;
+  p.y = lat;
+  return p;
+}
+
+export var names = ["cea"];
+export default {
+  init: init,
+  forward: forward,
+  inverse: inverse,
+  names: names
+};