[Proj] Lat/long to utm easting error

[Jérôme Cuinet]

Or you use a direct cylindric projection such as Cylindric Lambert, Behrman,
Peters... :)


Jérôme

2011/1/6 Noel Zinn (cc) <ndzinn at comcast.net>

> Adam,
>
> What you're expecting works only on the Central Meridian (CM) and not
> elsewhere due to convergence of the meridians.
>
> Google "convergence of the meridians" for a fuller explanation.
>
> Noel
>
> Noel Zinn, Principal, Hydrometronics LLC
> +1-832-539-1472 (office), +1-281-221-0051 (cell)
> noel.zinn at hydrometronics.com (email)
> http://www.hydrometronics.com (website)
>
> -----Original Message-----
> From: Adam Dershowitz
> Sent: Wednesday, January 05, 2011 6:18 PM
> To: proj at lists.maptools.org
> Subject: [Proj] Lat/long to utm easting error
>
> I have run into something that I don't understand, and I hope someone can
> help explain.
> I was doing some conversions of points, and ran into a problem.  I finally
> narrowed it down to the following:
>
> If I take two points, at the identical longitude, with a small change in
> latitude, and convert them each to UTM, I would expect nearly identical
> easting values.  But I am not seeing that.  For example:
>
> cs2cs +proj=latlong +datum=WGS84 +to +proj=utm +datum=WGS84 +zone=17 -r
>
> 42d37'3.77503"N 83d59'35"W
> 254524.57 4722707.58 0.00
> 42d37'0.02186"N 83d59'35"W
> 254520.47 4722591.80 0.00
>
>
> Above there is  ~4 m easting difference, with just a small (~120m) change
> in
> latitude.  Since these points are exactly North-south of each other,
> shouldn't they have the same easting, at least when they are this close to
> each other in latitude?
>
> Thanks much for any explanations,
>
> --Adam
>
>
>
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