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Frank Warmerdam | 3 Apr 2003 19:38
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[GRASSLIST:5954] Re: Krovak / PROJ4 (+axis option?)

Radim Blazek wrote:
> Hi Frank,
> 
> as you probably know, Krovak defines X=-y, Y=-x, i.e. X is vertical axis, 
> oriented down and Y is horizontal oriented to the left. But all
> GIS/GPS/... systems must use usual coordinate system where 
> coordinates are in 3. quadrant.
> For example:
> 14.39862613611E 50.465671925N  LL
> X=1001120.05 Y=738666.75       Krovak
> x=-738666.75 y=-1001120.05     In usual coor system and all GIS
> 
> Because:
> 1) Evenden's implementation of Krovak (PJ_kocc.c) returns by default
>    values in 3. quadrant (-738666.75 -1001120.05) and Krovak X,Y
>    is returned only with +czech option
> 2) All GIS applications require coor in 3. quadrant and there 
>    is no reasonable way to switch axis outside PROJ4 only for Krovak
>    (For GRASS for example, I used code PJ_krovak.c from PROJ4
>     but modified the code to get negative signs.)
> 3) Current behaviour in PROJ4 is wrong anyway in my opinion, because
>    returns 738666.76,1001120.13 (switched signs but not axis)
> 
> I suggest to change PJ_krovak.c in PROJ.4 as you can see below.
> That means to get values that most of applications require.
> 
> Radim
> 
> 136,137c139,140
> <       xy.y = ro * cos(eps) / a;
(Continue reading)

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Karl Swartz | 3 Apr 2003 20:35
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Re: Proj.4 vs Geotrans

Peter,

> See "Principle of Least Damage" in
> 
>  http://www.unicom.com/pw/reply-to-harmful.html

That is an excellent writeup!  Thank you for sending the URL.

 -- Karl
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Gerald I. Evenden | 4 Apr 2003 00:01
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Re: Re: Krovak / PROJ4 (+axis option?)

I'm probably missing something but if you want positive x-y in
the first quadrant why not specify a false easting/northing to
push everthing up and right.  No 'czech' option though.

The mathematical origin is at the shifted pole, up near Helsinki
and the area of interest is south and west of there, thus the
negative values in the natural solution.

That's too simple so I guess I missing something.  :-(

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Alexander Weidauer | 9 Apr 2003 13:47
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Inverse function of a quadrant is wrong?

Hi Folks,

I have a probleem with inverse projection.
To test my API in terms of NAN results
use following code:

     Writeln;

Writeln('-------------------------------------------------------------------');
     Writeln(' Numeric vaidation test');

Writeln('-------------------------------------------------------------------');
     Writeln('..open "+ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0"');
     Proj.Open('+ellps=WGS72  +proj=stere +lon_0=0 +lat_0=0');

Writeln('-------------------------------------------------------------------');
     Writeln('srcX [deg] srcY [deg]: destX [m] destY[m] , backX [deg] 
backY [deg]');

Writeln('-------------------------------------------------------------------');

     Calc(-180,-180);
     Calc(-135, -135);
     Calc( -90, -90);
     Calc( -45, -45);
     Calc(   0,   0);
     Calc(  45,  45);
     Calc(  90,  90);
     Calc( 135, 135);
     Calc( 180, 180);
(Continue reading)

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Alexander Weidauer | 9 Apr 2003 15:24
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ANN: update OpenSource Proj API to version 4.4.7/4.4.6

Hi folks,

Sorry, a little bit late because since 31 March the version 4.4.7
of geographic projection toolkit proj is out.

Ok here is the new OpenSource Delphi API version
of this toolkit with delphi and cbuilder api's and
the libraries proj447.lib and proj447.dll a new demo
witch containes a simple proj coordinate wrapper
for delphi (in cbuilder it is done). A binary distribution
of the proj.exe, geod.exe, cs2cs, nad2nad, nadgrid for
Windows NT compiled with BCC55 is also available

You can download the stuff freely with source from

http://www.triplexware.huckfinn.de/geogfix.html#proj.

Have fun Alex Weidauer

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Gerald I. Evenden | 9 Apr 2003 22:36
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Re: Inverse function of a quadrant is wrong?

The ellipsoid inverse for PROJ.4 stereographic does seem to have
a problem in the equitorial and oblique modes.  I will look into
it and hopefully have a corrected version in a couple of days.

One note however, some of the example numbers used exceeded
90d latitude which should induce an error condition.  Also
the antipodal value should also yield an error for stereographic.

(Antipodal: coordinate in the opposite of the earth from
from the lat_0, lon_0 coordinate.)

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Alexander Weidauer | 9 Apr 2003 22:56
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Re: Inverse function of a quadrant is wrong?

Hi Gerald,

Ok I've tested it with other proj oringins but was confused by the
results. So I went back to lat_0=0, lon_0=0. I can test it for other 
origins. The aim of my application is to show the usage of proj api
in an animation so I start to calculate NAN conditions for stere
initial origins. I want to create a animation over a moving origin
with a world map and a grid and render the image set.

Thanks Alex

Gerald I. Evenden schrieb:
> The ellipsoid inverse for PROJ.4 stereographic does seem to have
> a problem in the equitorial and oblique modes.  I will look into
> it and hopefully have a corrected version in a couple of days.
> 
> One note however, some of the example numbers used exceeded
> 90d latitude which should induce an error condition.  Also
> the antipodal value should also yield an error for stereographic.
> 
> (Antipodal: coordinate in the opposite of the earth from
> from the lat_0, lon_0 coordinate.)
> 
> ----------------------------------------
> PROJ.4 Discussion List
> See http://www.remotesensing.org/proj for subscription, unsubscription
> and other information.
> 

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(Continue reading)

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Gerald I. Evenden | 10 Apr 2003 18:39
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Re: Inverse function of a quadrant is wrong?

You lost me.  I can understand an animation of shifting origin but
I do not understand the need for the inverse.  Secondly, if the
animation is more-or-less global in extent the spherical form
would seem more appropriate.

None of this excuses the apparent failure of PROJ.4 to do a
proper inverse.

This all brings me back to my recent nemesis: the Gaussian Sphere:
I still have not resolved the differences between Snyder, Thomas,
Pearson, Swiss Projection, Krovak and alternate stereographic.
Some of these folk have elided the constants of integration
and I can't figure out why and what justification was used.
Are there any good mathematical cartographers out there who
have been through this material?

Snyder seems to use the conformal sphere as an intermediate
step in the stereographic but I can' simply match the procedures
with what I have done with the other examples.  AARRRRGGGHHHH!

On Wed, 2003-04-09 at 16:56, Alexander Weidauer wrote:
> Hi Gerald,
> 
> Ok I've tested it with other proj oringins but was confused by the
> results. So I went back to lat_0=0, lon_0=0. I can test it for other 
> origins. The aim of my application is to show the usage of proj api
> in an animation so I start to calculate NAN conditions for stere
> initial origins. I want to create a animation over a moving origin
> with a world map and a grid and render the image set.
>
(Continue reading)

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Clifford J Mugnier | 10 Apr 2003 20:57
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Re: Inverse function of a quadrant is wrong?


Gerald,

If you're looking at Equivalent Spheres, an extra bit of heartburn can be
garnered from a perusal of General Jean Laborde's Oblique Mercator of
Madagascar.  The dear general did, in fact, use a constant of integration.
It only took me a week or so (MANY years ago) to duplicate that one with an
HP calculator ...

Cliff Mugnier
LOUISIANA STATE UNIVERSITY

You lost me.  I can understand an animation of shifting origin but
I do not understand the need for the inverse.  Secondly, if the
animation is more-or-less global in extent the spherical form
would seem more appropriate.

None of this excuses the apparent failure of PROJ.4 to do a
proper inverse.

This all brings me back to my recent nemesis: the Gaussian Sphere:
I still have not resolved the differences between Snyder, Thomas,
Pearson, Swiss Projection, Krovak and alternate stereographic.
Some of these folk have elided the constants of integration
and I can't figure out why and what justification was used.
Are there any good mathematical cartographers out there who
have been through this material?

Snyder seems to use the conformal sphere as an intermediate
step in the stereographic but I can' simply match the procedures
(Continue reading)

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Alexander Weidauer | 10 Apr 2003 23:03
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Re: Inverse function of a quadrant is wrong?

Hi Gerald,

Sorry to arge you about this theme, but I hoped that I got propper
exceptions or overflow remarks will ocour, if the coodinates leaves the 
space of correct or possible  solution. For the stere it is quite simple 
to determin the range of propper coordinate solutions. But if somebody 
use the API  whith no idea of projections, the programmer (in this case 
I) has to prevent the errors by the API.

The inverse is not so mutch relevant for the animation but more for 
other demos or applications, witch have a  cursor over the map image 
that shows both (plain coordinates and longitude latitude coordinates) 
in a status panel and this will fail.

Never than less, thank you for your help.
Regards Alex Weidauer.

Gerald I. Evenden schrieb:
> You lost me.  I can understand an animation of shifting origin but
> I do not understand the need for the inverse.  Secondly, if the
> animation is more-or-less global in extent the spherical form
> would seem more appropriate.
> 
> None of this excuses the apparent failure of PROJ.4 to do a
> proper inverse.
> 
> This all brings me back to my recent nemesis: the Gaussian Sphere:
> I still have not resolved the differences between Snyder, Thomas,
> Pearson, Swiss Projection, Krovak and alternate stereographic.
> Some of these folk have elided the constants of integration
(Continue reading)

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Gmane