This example uses a custom projection (EPSG:27700) to display mapping from the free OpenSpace service from Ordnance Survey.

The OS OpenSpace layer is a WMS and has a tile size which changes with resolution (zoom).

See the os-graticule.js source to see how this is done using the OpenSpace OL3 class in openspace-ol3.js and an upgraded ol3 Graticule in graticule.js and an upgraded file here geodesicflatgeom.js