I received this response from MapInfo, which implies that the list of NADCON grid files used by MapInfo Pro is hardcoded. Not that it particularly matters to me, but I'd already put my two cents' worth into this discussion.
I'd gone by my experience with the original NADCON software and an earlier statement that NGS might have NADCON grid files for Mexico. However, a visit to the NGS website turned up no mention of them. Further research showed that Canada and some other Commonwealth countries use a different piece of software for grid-based datum conversions, including NAD27-NAD83. There's also something called MEXICO97 which calculates geoid heights, but whether that can be used for datum conversion is beyond my limited knowledge of geodesy. I've a feeling the original poster was more interested in using Mexico NAD 27 data than using the NADCON algorithm built into MapInfo for higher accuracy interoperability with NAD 83, so it probably doesn't matter to him either. Hope this helps Spencer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Thursday, August 24, 2006 3:28 PM To: Spencer Simpson Subject: RE: [MI-L] Mexico NAD27 Spencer: There's no NADCON datum shift\distortion grid file for Mexico or Canada in MI Pro. Outside of CONUS, Alaska, and a couple small island territory regions, MI Pro relies on Molodensky or Bursa-Wolfe methods for datum conversions when using NAD72\83 datums. Exceptions are for France which has an RGF93 grid, Japan which has a JGD2000 grid file, or Finland, which has a unique algorithm for doing Finnish - KKJ coordsys & datum conversions in MI Pro). The *.las and *.los files in your MI Pro program directory are the files we use for NADCON conversions in these areas. MI Pro already has the NAD27 datum for Mexico - #72. Typically users just substitute datum #72 into an existing mapinfow.PRJ file entry when working with data from Mexico based on this datum. Regards, -Bill Mail List:mapinfo-l-bounces From: "Spencer Simpson" <[EMAIL PROTECTED]> on 08/24/2006 01:04 PM AST To: <[email protected]> cc: <[email protected]> Subject: (Document link: MapInfo -L and Co.)RE: [MI-L] Mexico NAD27 I'm not sure that the list of NADCON datafiles used isn't hardcoded into MapInfo. I think someone from MapInfo will have to verify this. If you're working on a small area, the NGS website should also have a program called NADGRD, which lets you make extracts from the full NADCON datafile. A smaller grid file may speed up processing if it gets small enough to fit in the hard disk cache (and if MapInfo will let you use it). For example, I use an extract I made for Maryland in a specialized application. Hope this helps Spencer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Clifford J Mugnier Sent: Thursday, August 24, 2006 11:56 AM To: Keith Fowlow Cc: [email protected] Subject: Re: [MI-L] Mexico NAD27 Keith, The U.S. National Geodetic Survey (www.ngs.noaa.gov) has the software and data files to perform datum shifts (from NAD27 to NAD83) for the Republic of Mexico. I would guess that all you would need to do is to download the NADCON data files for Mexico into the appropriate subdirectory of your MapInfo package, and you'd be set up. Clifford J. Mugnier, C.P., C.M.S. National Director (2006-2008), Photogrammetric Applications Division American Society for Photogrammetry and Remote Sensing and Chief of Geodesy, CENTER FOR GEOINFORMATICS Department of Civil Engineering CEBA 3223A LOUISIANA STATE UNIVERSITY Baton Rouge, LA 70803 Voice and Facsimile: (225) 578-8536 [Academic] Voice and Facsimile: (225) 578-4474 [Research] Honorary Life Member of the Louisiana Society of Professional Surveyors ====================================================== http://www.asprs.org/resources/GRIDS/ http://appl003.lsu.edu/eng/ceeweb.nsf/$Content/Mugnier ====================================================== Fellow Users, I'm just getting into a project in Mexico. Got some SID pictures of the countryside and would like to register them correctly. The coordinate system is NAD27 Zone 15 for Mexico. Looking under the coordinate systems in MapInfo, there isn't a NAD27 for Mexico. Just for Canada and the US. Is there another system I should be using or will the NAD27 ConUS be good. Thanks, Keith Fowlow _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l
