[gdal-dev] stere

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[gdal-dev] stere

Patrick L. Francis

Hello! I have been banging my head against the wall trying to use the polar stereographic projection, and am hoping one of you that is smarter than me, which would likely be all of you can help! :-) lol

this projection:

when applied via gdal_translate and converted to mercator, results in.. how to describe? well here is a screenshot if you are interested

and here is what the original looks like before the projection is assigned and warped (I know the merc warp is good, because I use it on many other things.. I've just never tried polar stereographic before):

so clearly i'm doing something wrong... I've tried varations of lat_ts like this:
#cs2cs +proj=latlong +datum=WGS84 +to +proj=stere +lat_ts=37 +ellps=WGS84 +lat_0=90 +lon_0=-105 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
#cs2cs +proj=latlong +datum=WGS84 +to +proj=stere +lat_ts=7.838 +ellps=WGS84 +lat_0=90 +lon_0=-105 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs

because i'm not sure what "La1 7.838N" and such mean on that projection above...

Anyway, I hope someone can help lead me away from the dark side and into the light... this is driving me bonkers!  *ALIEN*

cheers,

--BlindLeper




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Re: stere

mccorb
I work with NWS grids a lot for nexrad data. They are in a 1/40 lfm grid. Your data looks like it might be an a 1/1 LFM grid. Here is the WKT I would use for a 1/1 LFM grid. Each cell is 190.5 km. 

PROJCS["1/1.0 LFM",GEOGCS["NOT SPECIFIED",DATUM["SPHERE",SPHEROID["SPHERE",6371200.0,0.0]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Stereographic_North_Pole"],PARAMETER["False_Easting",11.0],PARAMETER["False_Northing",41.0],PARAMETER["Central_Meridian",-105.0],PARAMETER["Standard_Parallel_1",60.0],PARAMETER["Scale_Factor",1],UNIT["190500.0 meters",190500.0]]

A 1/40 lfm grid projection that the NWS uses for the radar looks like so. The other one above is a wild guess based on the fact that it has a grid size of 190.5km I am thinking it is their LFM.

PROJCS["1/40.0 LFM",GEOGCS["NOT SPECIFIED",DATUM["SPHERE",SPHEROID["SPHERE",6371200.0,0.0]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Stereographic_North_Pole"],PARAMETER["False_Easting",401.0],PARAMETER["False_Northing",1601.0],PARAMETER["Central_Meridian",-105.0],PARAMETER["Standard_Parallel_1",60.0],PARAMETER["Scale_Factor",1],UNIT["4762.5 meters",4762.5]]

Good luck!

On Fri, Jul 14, 2017 at 8:56 AM, Patrick L. Francis <[hidden email]> wrote:

Hello! I have been banging my head against the wall trying to use the polar stereographic projection, and am hoping one of you that is smarter than me, which would likely be all of you can help! :-) lol

this projection:

when applied via gdal_translate and converted to mercator, results in.. how to describe? well here is a screenshot if you are interested

and here is what the original looks like before the projection is assigned and warped (I know the merc warp is good, because I use it on many other things.. I've just never tried polar stereographic before):

so clearly i'm doing something wrong... I've tried varations of lat_ts like this:
#cs2cs +proj=latlong +datum=WGS84 +to +proj=stere +lat_ts=37 +ellps=WGS84 +lat_0=90 +lon_0=-105 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
#cs2cs +proj=latlong +datum=WGS84 +to +proj=stere +lat_ts=7.838 +ellps=WGS84 +lat_0=90 +lon_0=-105 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs

because i'm not sure what "La1 7.838N" and such mean on that projection above...

Anyway, I hope someone can help lead me away from the dark side and into the light... this is driving me bonkers!  *ALIEN*

cheers,

--BlindLeper




..


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Re: stere

Patrick L. Francis

I work with NWS grids a lot for nexrad data. They are in a 1/40 lfm grid. Your data looks like it might be an a 1/1 LFM grid. Here is the WKT I would use for a 1/1 LFM grid. Each cell is 190.5 km. 

thank you for replying brian.... :-) the output using those specs ended up looking like:

from: +proj=stere +lat_0=90 +lat_ts=60 +lon_0=-105 +k=1 +x_0=0 +y_0=0 +a=190500.0  +b=190500.0 +units=m +no_defs

it's really amazing how changes look similar.. you can see where florida is on the image compared to google earth... there's got to be something really obvious i'm missing... wish I understood this stuff better.. *ALIEN*

thanks for trying *SPOCK*


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Re: stere

Andre Joost
Am 14.07.2017 um 19:06 schrieb Patrick L. Francis:

>
>> I work with NWS grids a lot for nexrad data. They are in a 1/40 lfm
>> grid. Your data looks like it might be an a 1/1 LFM grid. Here is the
>> WKT I would use for a 1/1 LFM grid. Each cell is 190.5 km.
>
> thank you for replying brian....  the output using those specs ended up
> looking like:
> http://www.blindleper.com/files/gdal/brian_mccormick_try.jpg
>
> from: +proj=stere +lat_0=90 +lat_ts=60 +lon_0=-105 +k=1 +x_0=0 +y_0=0
> +a=190500.0  +b=190500.0 +units=m +no_defs
>

a and b are the parameters for the ellipsoid, which seem totally wrong
now. Brian suggested a scale factor, which would be +to_meter instead of
+units=m.

If you run gdalsrsinfo on a text file with brian's WKT, it reports:

PROJ.4 : '+proj=stere +lat_0=90 +lat_ts=60 +lon_0=-105 +k=1 +x_0=2095500
+y_0=7810500 +a=6371200 +b=6371200 +to_meter=190500 +no_defs '

HTH,
André Joost


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