Newbie Polar stereographic question

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Newbie Polar stereographic question

john star

Hello!

I got image from a korean customer which is polar stereographic with center
Longitude=127, and center latitude = 35
The true latitude is 60. How do I use polar stereographic in this case ? Is
it possible to specify true lat other than
90 or -90 ?

Thanks!
    John
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Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Tuesday 11 July 2006 2:29 pm, starjohn wrote:
> Hello!
>
> I got image from a korean customer which is polar stereographic with center
> Longitude=127, and center latitude = 35
> The true latitude is 60. How do I use polar stereographic in this case ? Is
> it possible to specify true lat other than
> 90 or -90 ?

"Polar" Stereographic may be a bit of a misnomer.  I suspect simple
Steregraphic is  what is meant with the point of tangency at 127E? and 35N?.
In proj4 terms: +lat_0=127E +lat_0=35N.

I cannot imagine anyone using truly polar stereographic at a latitude of 35
degrees.

--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Newbie Polar stereographic question

john star
In reply to this post by john star

Hello Gerald!

Thanks a lot for the reply!

As far as I know, the projection plane is on latitude 60 and parallel to the
equator (this is the meaning of true latitude).

There is a ray from the center of earth to this plane. The center of the
projection
is the point on this plane where the ray from the center of earth goes
through the center
point and "meets" the plane.. this is the center of the projection. Makes a
sense ?

There is a drawing on mathworld to see this in better detail on
http://mathworld.wolfram.com/StereographicProjection.html

Thanks again and all the best
   John

> On Tuesday 11 July 2006 2:29 pm, starjohn wrote:
>> Hello!
>>
>> I got image from a korean customer which is polar stereographic with
>> center
>> Longitude=127, and center latitude = 35
>> The true latitude is 60. How do I use polar stereographic in this case ?
>> Is
>> it possible to specify true lat other than
>> 90 or -90 ?
>
> "Polar" Stereographic may be a bit of a misnomer.  I suspect simple
> Steregraphic is  what is meant with the point of tangency at 127E? and
> 35N?.
> In proj4 terms: +lat_0=127E +lat_0=35N.
>
> I cannot imagine anyone using truly polar stereographic at a latitude of
> 35
> degrees.
>
> --
> Jerry and the low-riders: Daisy Mae and Joshua
> "Cogito cogito ergo cogito sum"
>   Ambrose Bierce, The Devil's Dictionary
>
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Re: Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Wednesday 12 July 2006 2:22 pm, starjohn wrote:

> Hello Gerald!
>
> Thanks a lot for the reply!
>
> As far as I know, the projection plane is on latitude 60 and parallel to
> the equator (this is the meaning of true latitude).
>
> There is a ray from the center of earth to this plane. The center of the
> projection
> is the point on this plane where the ray from the center of earth goes
> through the center
> point and "meets" the plane.. this is the center of the projection. Makes a
> sense ?

Basically.  The source point of all the rays is the "antipod" of the point of
tangency of the projection plane.  That is at a point -lat_0,-lon_0.  Thus
the ray from the ray source to lat_0, lon_0 passes through the center of the
earth.  And the plane of the projection is orthogonal to this ray.

> There is a drawing on mathworld to see this in better detail on
> http://mathworld.wolfram.com/StereographicProjection.html
>
> Thanks again and all the best
>    John
>
> > On Tuesday 11 July 2006 2:29 pm, starjohn wrote:
> >> Hello!
> >>
> >> I got image from a korean customer which is polar stereographic with
> >> center
> >> Longitude=127, and center latitude = 35
> >> The true latitude is 60. How do I use polar stereographic in this case ?
> >> Is
> >> it possible to specify true lat other than
> >> 90 or -90 ?
> >
> > "Polar" Stereographic may be a bit of a misnomer.  I suspect simple
> > Steregraphic is  what is meant with the point of tangency at 127E? and
> > 35N?.
> > In proj4 terms: +lat_0=127E +lat_0=35N.
> >
> > I cannot imagine anyone using truly polar stereographic at a latitude of
> > 35
> > degrees.
> >
> > --
> > Jerry and the low-riders: Daisy Mae and Joshua
> > "Cogito cogito ergo cogito sum"
> >   Ambrose Bierce, The Devil's Dictionary
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj

--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Wednesday 12 July 2006 5:07 pm, Gerald I. Evenden wrote:

> On Wednesday 12 July 2006 2:22 pm, starjohn wrote:
> > Hello Gerald!
> >
> > Thanks a lot for the reply!
> >
> > As far as I know, the projection plane is on latitude 60 and parallel to
> > the equator (this is the meaning of true latitude).
> >
> > There is a ray from the center of earth to this plane. The center of the
> > projection
> > is the point on this plane where the ray from the center of earth goes
> > through the center
> > point and "meets" the plane.. this is the center of the projection. Makes
> > a sense ?
>
> Basically.  The source point of all the rays is the "antipod" of the point
> of tangency of the projection plane.  That is at a point -lat_0,-lon_0.
I should say lon_0+180

> Thus the ray from the ray source to lat_0, lon_0 passes through the center
> of the earth.  And the plane of the projection is orthogonal to this ray.
>
> > There is a drawing on mathworld to see this in better detail on
> > http://mathworld.wolfram.com/StereographicProjection.html
> >
> > Thanks again and all the best
> >    John
> >
> > > On Tuesday 11 July 2006 2:29 pm, starjohn wrote:
> > >> Hello!
> > >>
> > >> I got image from a korean customer which is polar stereographic with
> > >> center
> > >> Longitude=127, and center latitude = 35
> > >> The true latitude is 60. How do I use polar stereographic in this case
> > >> ? Is
> > >> it possible to specify true lat other than
> > >> 90 or -90 ?
> > >
> > > "Polar" Stereographic may be a bit of a misnomer.  I suspect simple
> > > Steregraphic is  what is meant with the point of tangency at 127E? and
> > > 35N?.
> > > In proj4 terms: +lat_0=127E +lat_0=35N.
> > >
> > > I cannot imagine anyone using truly polar stereographic at a latitude
> > > of 35
> > > degrees.
> > >
> > > --
> > > Jerry and the low-riders: Daisy Mae and Joshua
> > > "Cogito cogito ergo cogito sum"
> > >   Ambrose Bierce, The Devil's Dictionary
> >
> > _______________________________________________
> > Proj mailing list
> > [hidden email]
> > http://lists.maptools.org/mailman/listinfo/proj

--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Newbie Polar stereographic question

john star
In reply to this post by john star

Hi Gerald!

Thanks, I understand now that in libproj, the plane MUST be orthogonal
to the earth, and there is no support for this plane to be "inside" the
earth..

Is there a way to use the library for this case ? by playing with parameters
(btw,
what are the rest of parameters like lat_ts and k?), or it is just not
supported ?

Best Regards
   John

>Basically.  The source point of all the rays is the "antipod" of the point
>of tangency of the projection plane.  That is at a point -lat_0,-lon_0.
I should say lon_0+180
>Thus the ray from the ray source to lat_0, lon_0 passes through the center
>of the earth.  And the plane of the projection is orthogonal to this ray.
>


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Re: Newbie Polar stereographic question

john star
In reply to this post by john star

Hi Gerald!

Thanks, I understand now that in libproj, the plane MUST be orthogonal
to the earth, and there is no support for this plane to be "inside" the
earth..

Is there a way to use the library for this case ? by playing with parameters
(btw,
what are the rest of parameters like lat_ts and k?), or it is just not
supported ?

Best Regards
   John

>Basically.  The source point of all the rays is the "antipod" of the point
>of tangency of the projection plane.  That is at a point -lat_0,-lon_0.
I should say lon_0+180
>Thus the ray from the ray source to lat_0, lon_0 passes through the center
>of the earth.  And the plane of the projection is orthogonal to this ray.
>


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Re: Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Thursday 13 July 2006 2:13 am, john star wrote:
> Hi Gerald!
>
> Thanks, I understand now that in libproj, the plane MUST be orthogonal
> to the earth, and there is no support for this plane to be "inside" the
> earth..

In a sense, yes.  Using a scaling factor (k or k_0) of less than 1 turns the
projection plane into a secant plane.

> Is there a way to use the library for this case ? by playing with
> parameters (btw,
> what are the rest of parameters like lat_ts and k?), or it is just not
> supported ?

+lat_ts is used for the polar aspects and denotes the latitude at which the
scale is 1 (the place where the secant plane intersects the surface).

> Best Regards
>    John
>
> >Basically.  The source point of all the rays is the "antipod" of the point
> >of tangency of the projection plane.  That is at a point -lat_0,-lon_0.
>
> I should say lon_0+180
>
> >Thus the ray from the ray source to lat_0, lon_0 passes through the center
> >of the earth.  And the plane of the projection is orthogonal to this ray.
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj

--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Re: Newbie Polar stereographic question

OvV_HN
I wonder, can all 3 variants of the EPSG (OGP) stereographic projections be
calculated with (lib)proj's stere?

EPSG coordinate operation method 9810:
Polar Stereographic (variant A)
For Projected Coordinate Reference System: WGS 84 / UPS North

EPSG coordinate operation method 9829:
Polar Stereographic (variant B)
For Projected Coordinate Reference System: WGS 84 / Australian Antarctic
Polar Stereographic

EPSG coordinate operation method 9830:
Polar Stereographic (variant C)
For Projected Coordinate Reference System: Petrels 1972 / Terre Adelie Polar
Stereographic

Especially variants B and C still puzzle me a bit - in the sense of how to
do it with PROJ?

Probably not possible; the PROJ file "epsg" tells me for instance:
# Petrels 1972 / Terre Adelie Polar Stereographic
# Unable to translate coordinate system into PROJ.4 format.

Formulae and numerical examples can be found in the EPSG/OGP Guidance Note
7-2.


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Re: Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Thursday 13 July 2006 11:23 am, Oscar van Vlijmen wrote:
> I wonder, can all 3 variants of the EPSG (OGP) stereographic projections be
> calculated with (lib)proj's stere?

+proj=stere is probably OK for most polar aspects.  However, most non-US
oblique stereographic projections probably use +proj=sterea.  I am not sure
about equitorial needs as the problem does not seem to come up very often.

BTW, my previous statement about the projection ray trace is not true for the
oblique, elliptical stereographic because the normal to the projection plane
at the point of tangency to the *ellipse* does *not* pass through the center
of the earth.  It only passes through the center for all cases of the sphere
and only the polar and equitorial cases of the ellipsoid.

> EPSG coordinate operation method 9810:
> Polar Stereographic (variant A)
> For Projected Coordinate Reference System: WGS 84 / UPS North
>
> EPSG coordinate operation method 9829:
> Polar Stereographic (variant B)
> For Projected Coordinate Reference System: WGS 84 / Australian Antarctic
> Polar Stereographic
>
> EPSG coordinate operation method 9830:
> Polar Stereographic (variant C)
> For Projected Coordinate Reference System: Petrels 1972 / Terre Adelie
> Polar Stereographic
>
> Especially variants B and C still puzzle me a bit - in the sense of how to
> do it with PROJ?
>
> Probably not possible; the PROJ file "epsg" tells me for instance:
> # Petrels 1972 / Terre Adelie Polar Stereographic
> # Unable to translate coordinate system into PROJ.4 format.
>
> Formulae and numerical examples can be found in the EPSG/OGP Guidance Note
> 7-2.

--
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"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Re: Newbie Polar stereographic question

OvV_HN
> From: "Gerald I. Evenden"

>> I wonder, can all 3 variants of the EPSG (OGP) stereographic projections be
>> calculated with (lib)proj's stere?
> +proj=stere is probably OK for most polar aspects.  However, most non-US
> oblique stereographic projections probably use +proj=sterea.

I am afraid this is no useful answer for
>> EPSG coordinate operation method 9830:
>> Polar Stereographic (variant C)
>> For Projected Coordinate Reference System: Petrels 1972 / Terre Adelie
>> Polar Stereographic

Test case, from the EPSG/OGP guidance note 7.2:
International 1924 ellipsoid
lat=-66d36m8.820s; lon=140d4m17.040s;
latF=-67; lon0=140; x0=3e5; y0=2e5;
Result: x,y = 303169.521856971, 244055.720500674

The ESRI ArcGIS parameters try to 'fool' us with a false northing of
-2299363.487823496 instead of 2e5.
The parameters for (lib)proj stere are then:
International 1924 ellipsoid
lat=-66d36m8.820s; lon=140d4m17.040s;
lat_ts=-67; lon0=140; x0=3e5; y0=-2299363.487823496;
lat0=-90; k0=1;
This gives x,y: 303169.521856971, 244055.720507772

The northing is very close and an even better value of the false northing
would be -2299363.48783059.

I would suggest:

(a) Can someone give an exact formula producing a corrected false easting
for the general case, so that EPSG Polar Stereographic Variant C can be
calculated with (lib)proj.
(b) Or, add EPSG Variant C as an option to (lib)proj stere.
(c) Or simply state 'officially' that EPSG Variant C is not interesting
enough to devote any attention to it.







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Re: Re: Newbie Polar stereographic question

Gerald I. Evenden-2
On Friday 14 July 2006 8:12 am, Oscar van Vlijmen wrote:

> > From: "Gerald I. Evenden"
> >
> >> I wonder, can all 3 variants of the EPSG (OGP) stereographic projections
> >> be calculated with (lib)proj's stere?
> >
> > +proj=stere is probably OK for most polar aspects.  However, most non-US
> > oblique stereographic projections probably use +proj=sterea.
>
> I am afraid this is no useful answer for
>
> >> EPSG coordinate operation method 9830:
> >> Polar Stereographic (variant C)
> >> For Projected Coordinate Reference System: Petrels 1972 / Terre Adelie
> >> Polar Stereographic
>
> Test case, from the EPSG/OGP guidance note 7.2:
> International 1924 ellipsoid
> lat=-66d36m8.820s; lon=140d4m17.040s;
> latF=-67; lon0=140; x0=3e5; y0=2e5;
> Result: x,y = 303169.521856971, 244055.720500674
>
> The ESRI ArcGIS parameters try to 'fool' us with a false northing of
> -2299363.487823496 instead of 2e5.
> The parameters for (lib)proj stere are then:
> International 1924 ellipsoid
> lat=-66d36m8.820s; lon=140d4m17.040s;
> lat_ts=-67; lon0=140; x0=3e5; y0=-2299363.487823496;
> lat0=-90; k0=1;
> This gives x,y: 303169.521856971, 244055.720507772
>
> The northing is very close and an even better value of the false northing
> would be -2299363.48783059.
>
> I would suggest:
>
> (a) Can someone give an exact formula producing a corrected false easting
> for the general case, so that EPSG Polar Stereographic Variant C can be
> calculated with (lib)proj.
> (b) Or, add EPSG Variant C as an option to (lib)proj stere.
> (c) Or simply state 'officially' that EPSG Variant C is not interesting
> enough to devote any attention to it.

I an going to make a single comment: worrying about differences in the 1
micron range are pointless.  As long as the results compare to .1mm, call it
a match.  And even that may be a bit of overkill.

--
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"Cogito cogito ergo cogito sum"
   Ambrose Bierce, The Devil's Dictionary
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Re: Re: Newbie Polar stereographic question

OvV_HN
> From: "Gerald I. Evenden"
>>>> I wonder, can all 3 variants of the EPSG (OGP) stereographic projections
>>>> be calculated with (lib)proj's stere?
>>> +proj=stere is probably OK for most polar aspects.  However, most non-US
>>> oblique stereographic projections probably use +proj=sterea.
>> I am afraid this is no useful answer for
>>>> EPSG coordinate operation method 9830:
>>>> Polar Stereographic (variant C)
...
> I an going to make a single comment: worrying about differences in the 1
> micron range are pointless.

Probably a point is missed here.
(lib)proj is NOT capable of computing said projection.
I found out that a trick is needed: use an adapted false northing.
I asked for an equation, I got a micron :-)

Don't bother, in the mean time I've derived such an equation myself.
Anyone interested can mail me or post a reply here.
Variant B poses no difficulty if you know how to do it.

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Re: Re: Newbie Polar stereographic question

Clifford J Mugnier
In reply to this post by john star




Regarding the general philosopy of transformation accuracy alluded to
below, Mr. Evenden is correct in his statement.  The old classical
formulae, oftentimes being a "double" projection to the Equivalent Sphere
first, had an expected computational accuracy of 0.1 meter.

The new inertial datums referenced with GPS/GLONASS tools have projections
typically defined with an accuracy criterion of 0.1mm.

Expecting 0.1mm accuracy to "match" a 19th century projection math model is
as Mr. Evenden states, pointless.  It may be satisfying, but really has not
any realistic need.

Furthermore, most transforms and parameters offered by the EPSG have the
standard "oil patch" level of necessary computational accuracy, which is
0.1 meters.  Doing better than that does not do any better in finding where
to drill for oil and gas.  It's nice to have, but it's not necessary.

Clifford J. Mugnier C.P.,C.M.S.
National Director (2006-2008)
Photogrammetric Applications Division
AMERICAN SOCIETY FOR PHOTOGRAMMETRY AND REMOTE SENSING
and
Chief of Geodesy
Center for GeoInformatics
LOUISIANA STATE UNIVERSITY
Dept. of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70810
Voice:              (225) 578-8536
Facsimile:          (225) 578-8652
Corps of Engineers: (504) 862-1094 [Summertime]
-----------------------------------------------------------
http://www.ASPRS.org/resources/GRIDS
http://www.cee.lsu.edu/facultyStaff/mugnier/index.html
-----------------------------------------------------------


> From: "Gerald I. Evenden"
>>>> I wonder, can all 3 variants of the EPSG (OGP) stereographic
projections
>>>> be calculated with (lib)proj's stere?
>>> +proj=stere is probably OK for most polar aspects.  However, most
non-US
>>> oblique stereographic projections probably use +proj=sterea.
>> I am afraid this is no useful answer for
>>>> EPSG coordinate operation method 9830:
>>>> Polar Stereographic (variant C)
...
> I an going to make a single comment: worrying about differences in the 1
> micron range are pointless.

Probably a point is missed here.
(lib)proj is NOT capable of computing said projection.
I found out that a trick is needed: use an adapted false northing.
I asked for an equation, I got a micron :-)

Don't bother, in the mean time I've derived such an equation myself.
Anyone interested can mail me or post a reply here.
Variant B poses no difficulty if you know how to do it.

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Re: Re: Newbie Polar stereographic question

OvV_HN
In reply to this post by OvV_HN
>>>>> EPSG coordinate operation method 9830:
>>>>> Polar Stereographic (variant C)

> (lib)proj is NOT capable of computing said projection.
> I found out that a trick is needed: use an adapted false northing.

I know, virtually nobody is using it, so who cares?
But the one person that does need this projection in the general sense, can
do absolutely nothing with the ArcGIS fudge factor of -2299363.487823496 if
he wants to project from another ellipsoid or with another latitude of true
scale.
This needs another fudge factor or more sensibly, an equation.

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