[PROJ] [Proj] latlon projection

Pavel Hančar pavel.hancar at gmail.com
Sun Nov 18 17:24:49 EST 2018

```  Hi Luí­s,
<https://en.m.wikipedia.org/wiki/Equirectangular_projection> says the
Marinus of Tyre's projection is also called the equidistant cylindrical
projection. It implies, that the 'lonlat' and 'latlong' are just aliases
for 'eqc'. Right?  In that case I would expect to get this information
after I enter
\$ proj -l=lonlat
IMHO the output
lonlat : Lat/long (Geodetic)
does not say much.

I am just a beginner, so I might be wrong, but a note saying it's an alias
for 'eqc' could improve the description listing.

Best wishes,
Pavel

so 17. 11. 2018 v 23:52 odesílatel Luí­s Moreira de Sousa <
luis.de.sousa at protonmail.ch> napsal:

> 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.
>
> Regards.
>
> [0] https://en.m.wikipedia.org/wiki/Plate_carr%C3%A9e_projection
>
>
> Sent from ProtonMail mobile
>
>
>
> -------- Original Message --------
> On 17 Nov 2018, 21:03, Pavel Hančar < pavel.hancar at gmail.com> 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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