Support for Graticule Drawing for Grid Projections Other than EPSG4326

[dayanuyim]

Support for Graticule Drawing for Grid Projections Other than EPSG4326, with a additional option gridProjection

• modified: src/ol/geom/flat/geodesic.js

  • patch meridian() and parallel() to allow to pass the sourceProjection, instead of hardcoded EPSG4326

• modified: src/ol/layer/Graticule.js

  • add ctor options 'gridProjection', assign to property this.gridProjection_
  • use this.gridProjection_ to replace hardcoded EPSG4326
  • use gridProjection_.getExtent() to get the extent. (so users should define the extent for the gridProjection, if needed)
    (Originally, projection_.getWorldExtent() is used to do that, but it is only ok when gridProjection_ is EPSG4326)

• TODO: suggest to change the variables' name from lonlat to xy

Use Example:

import {addProjection, Projection} from 'ol/proj';
import {register} from 'ol/proj/proj4';
import proj4 from 'proj4';

// ref: https://epsg.io/<NUMBER>.js
// ref: http://mutolisp.logdown.com/posts/207563-taiwan-geodetic-coordinate-system-conversion
 proj4.defs([
   ["EPSG:3828", "+title=TWD67 TM2 Taiwan +proj=tmerc +lat_0=0 +lon_0=121 +k=0.9999 +x_0=250000 +y_0=0 +ellps=aust_SA +towgs84=-752,-358,-179,-0.0000011698,0.0000018398,0.0000009822,0.00002329 +units=m +no_defs"],
 ]);

// reigster for openlayers
register(proj4);

export const TWD67 = new Projection({
  code: 'EPSG:3828',
  //center: 252551.25 2611288.37
  extent: [ 145616.57, 2419514.81, 356704.34, 2803869.61 ],
  worldExtent: [119.99, 21.87, 122.06, 25.34 ],
  units: 'm',
});

addProjection(TWD67);


//-----------------------------------------------------

import {Stroke} from 'ol/style';
import Graticule from 'ol/layer/Graticule';

const tm2_label_formatter = n => {
  const s = Math.floor(n).toString();
  return s.slice(0, -3) + ' ' + s.slice(-3);
}

const layer = new Graticule({
  strokeStyle: new Stroke({
    color: 'rgba(64,64,64,1)',
    width: 2,
    lineDash: [0.5, 4]
  }),
  lonLabelPosition: 0,
  latLabelPosition: 0,
  lonLabelStyle: lonLabelStyle(),
  latLabelStyle: latLabelStyle(),
  showLabels: true,
  maxLines: 20,
  wrapX: true,
  intervals: [100000, 10000, 1000, 100, 10, 1],
  lonLabelFormatter: tm2_label_formatter,
  latLabelFormatter: tm2_label_formatter,
  targetSize: 80,
  gridProjection: 'EPSG:3828',  //TWD67
});