How to :: manage projections¶
What are projections ?¶
On a map, coordinates are generally expressed not as x
and y
as
in a plan.
Instead, a latitude
and a longitude
are provided to denote that
a location is a place on a sphere, rather than a plan.
Still, to represent this on a screen, which is a plan, we need to
convert these into regular planar coordinates. That’s where a
`projection
<https://en.wikipedia.org/wiki/Map_projection>`__ comes
in: a method to translate spherical coordinates into planar ones.
Many different projections exists, this part will
explain how to configure them, under the key projection
.
Default projection¶
By default, the Mercator projection (WGS 84) is assumed.
Warning
Tiles providers usually use this coordinate system. Changing to another would probably means breaking the tiles.
Planar coordinates¶
If geographical coordinates in your data are already projected on a
plan, set projection
to the value "plan"
.
This will use a simple cartesian projection.
Main use case for this is indoor maps.
Custom projection¶
Other projections are not supported for the moment, mainly because they would break tiles.
If your geographical data has been exported using another projection, please convert these the standard WGS 84 / EPSG 3857.
When importing a mesh file (BASEMAPS
section in the
etl_config.cson
file), if the input projection is precised
(mesh_projection
), we handle this conversion automatically.