# Newbie Polar stereographic question

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## Newbie Polar stereographic question

 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 _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Newbie Polar stereographic question

 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
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## Re: Newbie Polar stereographic question

 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.htmlThanks 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
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## Re: Re: Newbie Polar stereographic question

 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 _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Re: Newbie Polar stereographic question

 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 _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Newbie Polar stereographic question

 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. > _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Newbie Polar stereographic question

 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. > _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Re: Newbie Polar stereographic question

 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 _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Re: Newbie Polar stereographic question

 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. _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Re: Newbie Polar stereographic question

 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. -- 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
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## Re: Re: Newbie Polar stereographic question

 > 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. _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: Re: Newbie Polar stereographic question

 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. -- 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
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## Re: Re: Newbie Polar stereographic question

 > 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. _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj