[OSRS-PROJ] Error when forward projection with a polar stereo graphic projecti on.. Please help.

Frank Warmerdam warmerdam at pobox.com
Fri Dec 6 12:54:48 EST 2002

Ray Bryan E 2Lt 314 OSS/OSW wrote:
> Frank,
> Thanks for your help.  Everything seems to work now.  As for the false
> easting and northing numbers...  I was just using these as a test to input.
> Let me see if I'm straight on this.  False easting and northing is nothing
> more than an adjustment on the x,y plain?  So, if I'm going to make
> adjustments to fit screen x,y I will use this method?


I assume you could leave the x_0 and y_0 as zero.  For you the stereographic
coordiantes don't have any intrinsic significance, right?   You just convert
to stereographic and then stretch the result to your view window?  The
false easting and northing are used by convention in some predefined
coordinate systems primarily to keep the coordinates positive for easier
human use.

> Sorry for all of the questions, I'm new to GIS/Projection type stuff.  I
> have a steep learning curve.  I'm trying to draw a Polar Stereographic map
> of the US by reading a map file that contains lat/lon coastal data. I'm
> running input lat/lon data from the file through Proj4 and trying to get
> screen x,y to draw my coastal lines etc...  I have done this with a mercator
> projection and it was fairly simple.  I hope for the same by using Proj4.

No sweat.  To be truthful, I come at projections from a GIS perspective where
I have little understanding of the math. I am just reasonably good at plugging
parameters from various metadata formats into the projection functions.  I put
numbers in, I get numbers out, they match expectations and I am happy.  Note
that I didn't write PROJ.4, I am just the maintainer.

Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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