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On the field, quickly know where you are wrt to a grid or a path (eg : I am in grid B4, or I am at kilometer 2,3)
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When using a gridded printed map on the field, this quick app tells you the grid square or the location in kilometers on a parcours where you are currently standing.

Demo :



  • D7b is the grid square of the map where you are currently standing
  • 1.5 km is the kilometric index where you are currently standing

Usage :

  • to create the grid / parcours :

    • go to [url]
    • use 'Créer grille : créer', 'Créer parcours' ou 'Importer parcours'
    • draw the grid or the parcours
    • click on 'Partager' to show the url & QR-code
  • to know your current location :

    • enable geolocation
    • open the url, eg. [url]?scr,0,bea,del,LAT,LNG,Nx,Ny,invxy,revy


  • scr is the reference coordinate system (available options : 31370 : Lambert 72), or 0 for local TMercator
  • 0 is currently not used
  • del is the grid square length in meters
  • bea is the map azimuth in degrees
  • LAT,LNG are the WGS84 coordinates of the origin of the local TMercator coordinates system
  • Nx is the number of squares in X direction (horizontal)
  • Ny is the number of squares in Y direction (vertical)
  • invxy : if 0, use letters in x and figures in y. if 1, use figures in x and letters in y
  • revy : if 0, y coordinates is from top to bottom, if 0 from bottom to top
  • bm : the basemap to use (among the available basemaps)

The graphical user interface only allow to produces a grid in TMercator, with letters in x and figures in y (from top to bottom). But you may tweak the link afterwards.

Full example :,0,100,0,50.45019,5.95576,18,27,0,0

To use it operationnally

  • the x0, y0,delta,bearing should correspond to your printed map

  • x0,y0,delta,bearing,X0,Y0,Nx,Ny are generated by drawing a rectangle using [url]

  • you could send the link to your personnel by SMS/Whatsapp/...

  • or display it as a QR code

  • ideally, they can store the link on their smartphone home screen to use it when they need it

Enjoy !

Credits :

  • font-awesome-4.7.0
  • Leaflet.EasyButton-1.1.1
  • leaflet-1.3.1 (fork from va2ron1 2018-04-06)
  • Leaflet.Omnivore-0.3.3
  • Proj4Leaflet-0.7.0
  • hammer-2.0.8.js
  • jquery-2.1.1
  • tokml.js
  • download2.js


Presented @ FOSS4G-FR 15-17/5/2018 @ ENSG Paris

in Leaflet, modification of the toGeoJSON function, to also export the names of the elements :

LH.toGeoJSON = function (precision) {
    this.eachLayer(function (layer) {
        if (layer.toGeoJSON) {
            var json = layer.toGeoJSON(precision);        
            /*THIS SHOULD BE ADDED ->*/ if ( != null) if ( != '') =

to patch the minified code :

var o=i.toGeoJSON(t);

should be replaced by

var o=i.toGeoJSON(t); if(!=null) if(!='');
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