15 Apr 2012 22:19

## EPSG:3994 problem

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16 Apr 2012 11:27

### Re: EPSG:3994 problem

Hello Brent,

I don’t know why gdalinfo misinterprets the ESRI binary grid, or why spatialreference.org doesn’t help.

But EPSG:3994 uses Mercator variant B (see http://www.epsg.org/guides/docs/G7-2.pdf), which is a

somewhat unusual variant.

On the other hand, the epsg file of Proj version 4.8.0 has the same definition that you tried:

# WGS 84 / Mercator 41

<3994> +proj=merc +lon_0=100 +lat_ts=-41 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs  <>

which I believe is correct (lat_ts means latitude of true scale). Based on that, I can compute:

>proj +init=epsg:3994

100 0

0.00    0.00

101 41

84135.19        3767131.99

101 41.000009

84135.19        3767132.99

The first test point shows that the grid origin (zero easting, zero northing) is at

the equator at longitude 100 d E, which is what I would expect.

The other two test points shows that a difference of 0.000009 degrees in latitude,

near the latitude 41 N, gives a difference of about 1 meter in northing. This is also

what I would expect, since 41 N (and 41 S) are standard parallels, where the scale

should be true.  (Because 0.000009 degrees of latitude is about 1 meter.)

For your test point, I reproduce your results:

>proj -I +init=epsg:3994 -f "%.5f"

6200000.000 -3710000.000

173.69093       -40.48353

You say you didn’t expect these results:

> I expected values around 174.66  -41.41

but I don’t know if what you expected is correct or not. I have used Proj 4.8.0 that came with OSGeo4W.

On the other hand, in Proj 4.7.0 the epsg file had the entry

# WGS 84 / Mercator 41

<3994> +proj=merc +lon_0=100 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs  <>

which I think is very wrong.

The EPSG definition of WGS 84 / Mercator 41 used to have the code 3752, but

this was deprecated in 2008 and replaced with 3994 (EPSG change request 2008.088).

I am not sure if the bad definition in Proj 4.7.0 had anything to do with that, though.

Best regards,

Mikael Rittri

Carmenta

Sweden

http://www.carmenta.com

From: proj-bounces <at> lists.maptools.org [mailto:proj-bounces <at> lists.maptools.org] On Behalf Of pcreso <at> pcreso.com
Sent: den 15 april 2012 22:19
To: proj <at> lists.maptools.org
Subject: [Proj] EPSG:3994 problem

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