How to display a MGRS graticule?

[nboisteault]

Hi, I have seen this example : https://viglino.github.io/ol-ext/examples/canvas/map.control.graticule.html to display different graticule. I'd like to know how to display a graticule for MGRS (Military Grid Reference System).

[Viglino]

MGRS is derived from the Universal Transverse Mercator (UTM) grid system (see example). But an MGRS grid reference is a point reference system, much more than the DFCI grid (see https://viglino.github.io/ol-ext/examples/layer/map.dfci.html). There is no plans for adding something like this to the library. You can use the the mgrs library to convert lonlat to MGRS coordinates in an ol​/control​/MousePosition

[mike-000]

It could be done. You could create a custom projection in OpenLayers which combines all the UTM zones into a single projection, by adding 1000000 to the x coordinates for each zone number (the projections for the southern hemisphere zones are not needed as the northern projections work also there but with negative y values). Unfortunately the graticule https://codesandbox.io/s/mgrs-icewnm?file=/main.js is messy as lines are drawn at random multiples of step and rarely align with zone edges, and lines which should be curves are drawn straight.

Those problems could be fixed it the graticule had an intervals option similar to the OpenLayers graticule, and a precision option so lines can be calculated at a smaller interval than they are drawn https://codesandbox.io/s/mgrs-forked-q6q17i?file=/main.js

[Viglino]

@mike-000 great idea! Make a PR on the Graticule control file! I'll add your example to show how to use it.

[Viglino]

@mike-000 example is available et https://viglino.github.io/ol-ext/examples/canvas/map.control.graticule2.html

[nboisteault]

@mike-000 @Viglino how would you handle special cases like on Norway where grid is different? An example here : https://www.map.army/

[mike-000]

It would need special cases in the transforms, e.g. https://codesandbox.io/s/mgrs-forked-4km7cj?file=/main.js That is not quite correct as it should be based on latitude, not 1000 km UTM y coordinate edges

[nboisteault]

@mike-000 Maybe LLtoUTM and UTMtoLL functions from https://github.com/proj4js/mgrs/blob/c707a1e7f69c8f2564e65948da3ac295a87b547e/dist/mgrs.js could be used instead of ll2utm and utm2ll with some adaptations?