[PROJ] [Proj] latlon projection

Luí­s Moreira de Sousa luis.de.sousa at protonmail.ch
Mon Nov 19 02:35:27 EST 2018

Hi again Pavel,

the information provided by PROJ is correct, you just need to be aware that most software interpret it in a different way. In fact a cartographic programme like QGis should not portray datasets defined in a geodetical system, and always request an explicit projection. Depending on your goal, it is possibly wiser to use a cartographic system.


Luís Moreira de Sousa
Email: luis.de.sousa at protonmail.ch
RingID: ring:7ca91d83f4f9dec82fec9f1144b8e5c1ef2a110c
URL: https://ldesousa.github.io

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Sunday, 18 November 2018 23:24, Pavel Hančar <pavel.hancar at gmail.com> wrote:

>   Hi Luí­s,
>   Thank you for your answer. The [linked article](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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