[OSRS-PROJ] proj4 parameter question regarding UTM

[peter]

Hello,

	O.K., Thanks for the info. I looked at my central coords and they
come out reasonably cloase to what is expected.
I'll have to modify my code to change the UTM zone at each
boundary I guess.
	I also need to check my original method for generating UTM since
one of the two methods gives me about 9 meters of error near the center of
the zone. Of course this may be due to a lack of ellipsoid in *my* original
model.

I did notice that mapping outside the UTM zone with proj has a greater
error to the east. I'm not sure whay that is. Perhaps the polynomial equation
that is being used iterates from west to east.

Thanks again for your input.

Peter



On Friday 06 February 2004 04:53 pm, Ed McNierney wrote:
> Peter -
>
> If that's what you're looking for, you got the right answer.
>
> You concluded that it was wrong because you compared it to the zone 7
> northing and easting, not the pseudo-zone 10 values.
>
> While you can mathematically do what you're intending, you will get
> severe distortion in your data.  Using "tmerc instead" won't help - UTM
> is simply a particular form of tmerc, and using tmerc for such a large
> extent will produce a comparable degree of distortion.
>
> Depending on your application, that distortion might be acceptable.  The
> reason UTM zones are 6 degrees wide is based on a desire to limit the
> extent of that distortion.
>
> 	- Ed
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com
> -----Original Message-----
> From: pw [mailto:p.willis at telus.net]
> Sent: Friday, February 06, 2004 7:17 PM
> To: osrs-proj at remotesensing.org
> Subject: Re: [OSRS-PROJ] proj4 parameter question regarding UTM
>
> Hello,
>
> Yes, I want pseudo values in UTM zone 10 projection.
> I guess I could make a table of meridians and use tmerc instead.
>
> Peter
>
> > That lat, long is in zone 7.  You are trying to get a psuedo-zone
> > value, 3
>
> zones away.
>
>
>
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