[GIS] Using UTM in leaflet efficiently

leafletprojutm

Our server is using UTM internally. We then send a large number of UTM Coordinates to display them in a custom made leaflet layer.

First we transform (unproject) them into "normal" geographical coordinates using Proj4Leaflet . Then we use leaflets latLngToLayerPoint() function in order to project them for our custom layer.

The latLngToLayerPoint() function is projecting the geographic coordinates back into point coordinates.

Is there a way to transform our UTM coordinates directly into points without making the detour by geographical coordinates? I see that there is a transform() function which is used by Leaflet internally to project "normal" latlng coordinates.

How can I get the necessary parameters to perform a transformation from EPSG 32633 to the internal 3857 projection?

Best Answer

You can use the transform set up in proj4leaflet. I expect that you have already crated a CRS in your map.options.

var my_crs = map.options.crs; // get the CRS
var my_proj = my_crs.projection; // get the projection
// transform the lat lon Point to a utm point
var my_utm_point = my_proj.project(point_in_latlng);

If you want to set the internal coordinate system to UTM in leaflet I think you have to do a lot of recoding or use openLayers instead.

Related Solutions

[GIS] How to convert Lat/Long to UTM using Proj(4j) similar to JScience UTM.latLongToUTM

If you're using WGS84, for a northern hemisphere zone, concatenate 326 + zone number. For a southern hemisphere zone, concatenate 327 + zone number. The 326 comes from 4326, the code for a 2D WGS84.

So for zone 30N, 32630.

There are a few other drop-first-integer-and-concatenate-zone-number, but none as complete as WGS84. Others, like NAD83, the first zones added follow the same convention but later ones do not.

I should have made this a comment on simplexio's answer--vote for that answer!

[GIS] UTM Grid as a Layer with Leaflet

I can tell you the answer for the second question: How to show UTM-coordinates in the lower right corner.

In leaflet the internal coordinate system is always longitude/latitude as far as I know, and you have to transform every time you need to work with your data.

First make sure you have installed proj4.js and proj4leaflet.js. To show your coordinates you can use the plugin: https://github.com/ardhi/Leaflet.MousePosition .

Then define your coordinate system and use when you define your map object:

var crs = new L.Proj.CRS.TMS('EPSG:25832',
                              '+proj=utm +zone=32 +ellps=GRS80 +units=m +no_defs', 
                              [120000, 5900000, 1000000, 6500000], 
                              {resolutions: [1638.4, 819.2, 0.1]
});

var map = new L.Map('map', {
      crs: crs,
      continuousWorld: true,
      worldCopyJump: false
});

The function _onMouseMove() should be modified to something like this:

_onMouseMove: function (e) {
  var my_crs = map.options.crs; // get the coordinate system
  var my_proj = my_crs.projection; // get the projection, which makes the transform
  var my_point = my_proj.project(e.latlng); // Here we transform back to UTM
  var lng = my_point.x;
  var lat = my_point.y;
  var value = this.options.lngFirst ? lng + this.options.separator + lat : lat + this.options.separator + lng;
  var prefixAndValue = this.options.prefix + ' ' + value;
  this._container.innerHTML = prefixAndValue;
}

You will then get your mouse position in UTM. For more information see the documentation for proj4leaflet and leaflet.mouseposition.

Best Answer

Related Solutions

[GIS] How to convert Lat/Long to UTM using Proj(4j) similar to JScience UTM.latLongToUTM

[GIS] UTM Grid as a Layer with Leaflet

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