nad27 for mexico

[Oscar Guerra]

I need the NAD27 for mexico datum data to modify the mapinfow.prj
file.
Someone has it?
Please if posible tell me step by step how to modify the "prj" file in
order to use the datum.
Thanks a lot.
O- Guerra

[David R Sherrod]

This Mexico NAD27 query has been around for a while. It's always a surprise to see something go unanswered on MI-L

PART 1.  The projection lines needed
All the NAD27 datums use the Clarke ellipsoid (1866), I think.

My projection file MAPINFOW.prj has this line for Mexico in the basic Lat-Long scheme:
"Longitude / Latitude (NAD 27 for Mexico)", 1, 72

By the way, older versions (6.0 for example) had this mistyped as 69, which applies to Central American countries.

It gets more complex if you’re trying to add lines for UTM
Cindy Graubard posted these in a 2006 reply to Keith Fowlow.  You might contact Keith if you have problems, because other postings have suggested he has some experience trying to get maps projected correctly for Mexico. In the following lines, the negative value (longitude) varies depending on where the transverse cylinder slices through the globe.
"UTM Zone 11 (NAD 27 for MEXICO)", 8, 72, 7, -117, 0, 0.9996, 500000, 0
"UTM Zone 12 (NAD 27 for MEXICO)", 8, 72, 7, -111, 0, 0.9996, 500000, 0
"UTM Zone 13 (NAD 27 for MEXICO)", 8, 72, 7, -105, 0, 0.9996, 500000, 0
"UTM Zone 14 (NAD 27 for MEXICO)", 8, 72, 7, -99, 0, 0.9996, 500000, 0
"UTM Zone 15 (NAD 27 for MEXICO)", 8, 72, 7, -93, 0, 0.9996, 500000, 0
"UTM Zone 16 (NAD 27 for MEXICO)", 8, 72, 7, -87, 0, 0.9996, 500000, 0


PART 2.  How and where do you add it to your MAPINFOW.prj file?
Open the prj file in a text editor.  Copy and paste the lines of interest into the prj file.
Copy the line exactly as shown here.  The quotes in the front half bracket the title information, whereas the subsequent numeric entries frame the information for projection, datum, and other factors that MapInfo will use to project your data correctly.

If you're uncertain where to put the lines in the prj file, then first run a search (in the prj file) for Mexico.  See if your version is new enough to already have some Mexico lines embedded.
The first section of the prj file is Latitude / Longitude (that's the header, and it's in quotes in the file), and you could put the Lat/Long projection line in the appropriate place under that header.  (Alphabetical order is the existing scheme.)

For the other lines, run a search for UTM, and ultimately you'll find the header for UTM NAD 27.  Then poke around and decide where you'd choose to insert the projection lines.

--------------------------------------------
David R. Sherrod, Cascades Volcano Observatory
U.S. Geological Survey,
1300 SE Cardinal Court, Bldg. 10
Vancouver, WA  98683
voice 360-993-8915
fax     360-993-8980
dshe...@usgs.gov
-----------------------------------------

From:	Oscar Guerra <oguer...@gmail.com>
To:	MapInfo-L <mapi...@googlegroups.com>
Date:	09/08/2011 09:20 AM
Subject:	[MI-L] nad27 for mexico
Sent by:	mapi...@googlegroups.com

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[ssim...@baltometro.org]

I’m still trying to wrap my head around how there could be more than one NAD 27.   

 

Are these unofficial “tweaks” to NAD 27 that crept in to different national survey grids when maps didn’t line up?  Some sort of backtracking to interoperate with maps on later official datums?

 

Did Mexico and Canada officially redefine the point where the ellipsoid touches the Earth (In the US it’s Meades Ranch)? 

 

The most benign thing I can think of is that MapInfo simply needs different parameters to convert from other datums for different patches, to reduce the accumulation of calculation errors.

 

---

Spencer

[David R Sherrod]

Spencer,
I believe it is just as you suggest it.  Meades Ranch is still the point of reference, with geoid vertical height zero.  I am ignorant of the adjustments made to survey stations as the datum was applied more broadly across North America, but it must be something like that, and not simply a MapInfo-based correction.
Anecdotally, you'll find these distinctions for NAD27 Lat-long pop up as datum selections in handheld GPS receivers in play since the mid-1990s---like NAD 27 Cuba or NAD27 Greenland or NAD27 Mexico.

Dave Sherrod

-----------------------------------------

From:	<ssim...@baltometro.org>
To:	<mapi...@googlegroups.com>
Date:	09/12/2011 12:50 PM
Subject:	RE: [MI-L] nad27 for mexico
Sent by:	mapi...@googlegroups.com

---

[Oscar Guerra]

Thanks a lot to all specially to David.
Regards

Oscar G

On 12 sep, 13:41, David R Sherrod <dsher...@usgs.gov> wrote:
> This Mexico NAD27 query has been around for a while. It's always a
> surprise to see something go unanswered on MI-L
>
> PART 1.  The projection lines needed
> All the NAD27 datums use the Clarke ellipsoid (1866), I think.
>
> My projection file MAPINFOW.prj has this line for Mexico in the basic
> Lat-Long scheme:
> "Longitude / Latitude (NAD 27 for Mexico)", 1, 72
>
> By the way, older versions (6.0 for example) had this mistyped as 69,
> which applies to Central American countries.
>

> It gets more complex if you?re trying to add lines for UTM

> dsher...@usgs.gov
> -----------------------------------------

>
> From:
> Oscar Guerra <oguerra...@gmail.com>
> To:
> MapInfo-L <mapi...@googlegroups.com>
> Date:
> 09/08/2011 09:20 AM
> Subject:
> [MI-L] nad27 for mexico
> Sent by:
> mapi...@googlegroups.com
>