[GRASS-user] (re)projection question

Ken Mankoff mankoff at gmail.com
Thu Jan 21 13:34:32 PST 2016


Hi Helmut,

Yes it seems that I needed to add the key=value pair of "datum=wgs84" to the proj4 string. That was the only issue. I had not included it at first because it was not on the maptools website for Oblique Stereographic.

I'm now trying r.proj between the two projections...

  -k.


On 2016-01-21 at 16:09, Helmut Kudrnovsky <hellik at web.de> wrote:
> Helmut Kudrnovsky wrote
>> 
>> Ken Mankoff wrote
>>> Hi Helmut,
>>> 
>>> On 2016-01-21 at 11:45, Helmut Kudrnovsky <
>
>>> hellik@
>
>>> > wrote:
>>>> a quick internet search finds, e.g. 
>>>> http://geotiff.maptools.org/proj_list/oblique_stereographic.html
>>>> maybe a starting point.
>>> 
>>> I'd found that before, but thank you for sending the link again. I made
>>> progress on re-reading it.
>>> 
>>>> for a correct Proj.4 string to create a location, it's best to ask in
>>>> the
>>>> Proj.4 ML.
>>> 
>>> The progress I made, unfortunately, makes me unsure if this is a proj4 or
>>> a grass question. But I'm not sure.
>>> 
>>> I don't want to split this thread too much, but decided to try posting on
>>> GIS.SE since both communities might see it there.
>>> https://gis.stackexchange.com/questions/177763/how-to-define-proj4-string-for-grass
>>> 
>>> I'll post a resolution on this thread if I get an answer there.
>> on GIS.SE you posted a link to your data; see there:
>> 
>> https://nsidc.org/data/docs/daac/nsidc0092_greenland_ice_thickness.gd.html
>> 
>> " Projection
>> 
>> All grids are in a polar stereographic projection with reference to the
>> WGS84 ellipsoid. The standard parallel is 71°N, and the projection
>> parallel (latitude of the center of the projection) is 90°N. The North
>> Pole is the origin of the projection. The central meridian is 39°W."
>
> quick test:
>
> locatio wizzard -> create location by proj4 string:
>
> +proj=sterea +datum=wgs84 +lat_0=70.5 +lon_0=40 
>
> g.proj -j                                                                       
> +proj=sterea
> +lat_0=70.5
> +lon_0=40
> +k=1
> +x_0=0
> +y_0=0
> +no_defs
> +a=6378137
> +rf=298.257223563
> +towgs84=0.000,0.000,0.000
> +to_meter=1
>
> the location is created without any error; just adapt it for your need.
>
>
>
>
> -----
> best regards
> Helmut



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