[Vis5d-users] Re: Lambert Conformal Projection

Hello again,

just want to say that the problem has been
solved. Latitude of origin is either 90 or
-90 degrees. PoleRow/PoleColumn has to
be multiplied by columnIncrement and
we get the origin of the 3D-Box in
projected coords. I suggest more meaningful
names for those variables :-)

Thank you for reading,

	Antonio Bleile

P.S.: Have written some C++ code for transforming
lambda/phi <-> Lambert Conformal. If anybody is
interested.... Go and get it from me.

Antonio Bleile wrote:

> Hi List,
> 
> I have a problem with the Lambert Conformal projection.
> I have a textbook which contains all the
> formulas for the forward and inverse Lambert
> Conformal projection. The formulas work pretty
> well, but they are parameterized in a different
> manner than in Vis5D.
> 
> A Lambert Conformal projection is generally defined by:
> 
> 1. The two standard parallels
> 2. Latitude and longitude for
> the origin of the projected coordinates
> 
> A Vis5d Lambert Conformal projection is definded by:
> 
> Lambert Conformal projection:
>         Standard Latitude 1: 25.010000
>         Standard Latitude 2: 25.000000
>         North/South Pole Row: -126.380463
>         North/South Pole Column: 40.000000
>         Central Longitude: 95.000000
>         Column Increment: 81.269997 km
> 
> 
> OK, i got the standard parallels and the central
> longitude. The thing I'm missing is the latitude
> of the origin.....
> 
> It must be calculated somehow with PoleRow/Column.
> But I don't get it. I tried to calculate the latidude
> like this: Walk ColumnIncrement*PoleRow km from the
> north pole along the central logitude southwards and
> calculate the longitude. But this doesn't work. (My
> projected data is too much south or too much north...
> but the east/west alignment seems to work....)
> 
> Please can somebody explain in some more detail the
> meaning of PoleRow and PoleColumn?
> 
> 
> The only documentation I found is this:
> " PoleRow, PoleCol:  These parameters indicate the position of the north 
> or south pole with respect to the 3-D grid coordinate system. These 
> values may be outside the 3-D grid. If Lat1 and Lat2 are positive, the 
> north pole is assumed, else, the south pole is assumed."
> 
> So what is the 3-D grid coordinate system?
> 
> I would greatly appreciate your help.
> 
> Thanks and best regards,
> 
>     Antonio Bleile
> 
> 
> 
>