Which coordinate system to choose?

[sarthak0415]

boost.geomtery have various coordinate system here, which one to choose for osm data and do user have to be given an option to choose coordinate system .
If the user wants to choose which coordinate system he wants what do we need?

this is the cartisian model followed by osm.

[cvvergara]

@sarthak-0415
this is related to #43 what would be an appropiate flag for this?

[sarthak0415]

yes we should and name is csystem

[cvvergara]

csystem what is that?

[cvvergara]

oh, c for coordinate, c for conf

[sarthak0415]

yes and defalut value should the coordinate system we are using currently

[cvvergara]

yes is c for conf? I think the name should be more meaninful,

• coord (short for coordinate)

[cvvergara]

and can you tell me what is the coordinate system osm uses?

[cvvergara]

nd also what are the valid coordinate systems that we can accept?

[sarthak0415]

we use longitudes and lattitudes from the osm file
geographic coordinate system

[sarthak0415]

that I dont know but boost.geomtery supports these coordinate systems

• cartesian
• spherical
• spherical_equatorial
• geographic

[cvvergara]

@sarthak-0415
please find out what osm use, because that should be the default.
maybe @woodbri knows?

[sarthak0415]

OSM uses WGS84
http://wiki.openstreetmap.org/wiki/Converting_to_WGS84

[woodbri]

I would use a term the is common to postgis to refer to projections, what you are calling coordinate system. postgis uses "srid", GDAL/OGR uses "srs, ESRI uses a file extension "prj", there is not need to define yet another term and because the data is getting loaded into a postgis database we should be consistent with that.

OSM data generally can be found in WGS84 (aka: srid=4326) or Sperical Mercator (aka: srid=900913 or 3857). I think we should leave the provenance of reprojecting the data to postgis and focus on loading the the data.

[woodbri]

I'm for using WGS84, like I said users can use postgis to transform the data later to another coordinate system if they need that.

[cvvergara]

@sarthak-0415
can you ask to boost.geometry what coordinates system is convenient when the data is WGS84?

[dkastl]

I'm also for using WGS84 (EPSG:4326).
It's easy enough later to reproject if a user wants to have a different one.

osm2pgsql seems to use Spherical Mercator by default, so it can be used right away for rendering: https://help.openstreetmap.org/questions/6256/why-do-osm2pgsql-and-mapnik-use-spherical-projection-900913

It seems it also supports an -E 4326 flag, but i think we don't do this now. Someone can add this later.