[Proj] latlon projection

Luí­s Moreira de Sousa luis.de.sousa at protonmail.ch
Sat Nov 17 17:51:58 EST 2018

Hi Pavel,

that equates to Marinus of Tyre's projection [0]. Even though PROJ itself takes it as a geodetical coordinate system, pretty much all other software (Qgis, GRASS, etc) treats it as cartographic. You should keep this in mind when computing distances or areas in this system.


[0] https://en.m.wikipedia.org/wiki/Plate_carr%C3%A9e_projection

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-------- Original Message --------
On 17 Nov 2018, 21:03, Pavel Hančar wrote:

>   Hello,
> I am trying to understand some basic concepts of map rendering, but I've got really confused by the fact, that "longlat" or "lonlat" are often mentioned as a name of a projection. For example:
> +proj=longlat +datum=WGS84 +no_defs
> AFAIK longitude and latitude stay for a coordination system, not for a map projection. Thus I thought it was a kind of simplification and the actual projection must have been the Equidistant Cylindrical. But I found the  Equidistant Cylindrical being determined by "eqc" not "longlat".  So what is the "longlat"? I ended up running `proj -lP`, but found just this:
> lonlat : Lat/long (Geodetic)
> latlon : Lat/long (Geodetic alias)
> The only explanation is, that it is geodetic. But to me it seems it is not any explanation, but a further specification saying it is not geocentric, but the angles are taken from normals of the ellipsoid.
> So, what projection is the "lonlat"? Or how are longitude and latitude projected to the flat map when nothing else is specified?
>  Thank you very much.
>   Best wishes,
>   Pavel Hančar
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