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I want to define a custom crs valid for Mexico. The context is that older cartography in Mexico is based on the NAD27 datum. I wanted to test the following proj4 string

+proj=longlat +ellps=clrk66 +towgs84=-12,130,190,0,0,0,0 +no_defs

Nevertheless , when I test my string with 19N 99W (19,-99) I get the following values

enter image description here

testing the proj 4 definition included in Qgis gives the same results.

These are wrong since the resulting north should be around 19 and the resulting east around -99. I wonder if anyone can tell me what I am doing wrong. Thanks in advance

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1 Answer 1

up vote 2 down vote accepted

You are not doing wrong, I get the same strange result here. The testing box works well with projected CRS. I'm not sure if its a bug or a feature. If you want to make coordinate transformations, you could use cs2cs.

You have set up a string for a geographic (lat/lon) CRS. I guess that your old mexican maps are in some kind of projected CRS with units in metres or feet, so this custom CRS might not yet be that what you want to.

EDIT: I issued a bug report for it: http://hub.qgis.org/issues/7036.

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1  
the output values are in radians. Maybe you'll want to update the bug report? –  mkennedy Jan 23 '13 at 19:42
    
Thanks for computing. I also linked back from the bugtracker. –  Andre Joost Jan 23 '13 at 20:19
    
I made the conversion to degrees and now all make sense. Thanks –  Gerardo Jimenez Jan 24 '13 at 2:25

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