# [OSRS-PROJ] Pseudo X/Y values, forward and reverse

William Hersman Willy.Hersman at conocophillips.com
Wed Jan 29 20:19:11 EST 2003

```Input    -175.1234589    59.7654305  DD
Return   -4054878.4814   2990301.082 ASP 4 FEET
Input    -4054878.4814   2990301.082 ASP 4 FEET
Return   -175.1487387    59.7638269  DD

"Ed McNierney" <ed at topozone.com>
Sent by: owner-osrs-proj at remotesensing.org

01/29/2003 03:13 PM
Any replies will be addressed to: osrs-proj

To:   <osrs-proj at remotesensing.org>
cc:
Subject:    RE: [OSRS-PROJ] Pseudo X/Y values, forward and reverse

Willy -

Can you provide us with the numbers you're using in your sample?

Are you correctly interpreting and re-entering the lat/lon values?  It
sounds like you could be getting (for example) output lat/lon in degrees
and decimal minutes which is being input as degrees/minutes/seconds.

- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242   Fax: (978) 251-1396
ed at topozone.com

-----Original Message-----
From: William Hersman [mailto:Willy.Hersman at conocophillips.com]
Sent: Wednesday, January 29, 2003 6:07 PM
To: osrs-proj at remotesensing.org
Subject: [OSRS-PROJ] Pseudo X/Y values, forward and reverse

We are struggling with the following problem.  Perhaps someone could
comment.

Alaska has 10 Stateplane zones.  Let's say a point exists in zone 10 and
we
want the pseudo x/y for zone 4.  On forward projection the given
lat/long
returns x/y values calculated for zone 4. When one then re-inputs the
x/y
values into the algorithm to get a lat/long, the inverse does not return
to
the same point.  In fact, in terms of feet, it is nearly a mile off !
What
might be going wrong here, and should one expect to be able to
"round-trip"
a point when junmping across zones?

Thanks,

Willy Hersman

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