----- Original Message -----
From: "Berk Charlton" <[EMAIL PROTECTED]>
To: "mapinfo-l" <[EMAIL PROTECTED]>
Sent: Friday, September 08, 2000 3:28 PM
Subject: Need to change datum - was [RE: MI nad 27 to nad 83]
>
> Thanks for the many responses I received on this issue. [To summarize:
Use the
> "File-Save Copy As" command, and specify a new projection within that
dialog.]
>
> I should have clarified the problem a little better: I need to be able to
> change the DATUM of the .tab files from NAD 27 to NAD 83. For example,
when a
> file is converted using the above method, the datum apparently stays the
same.
> I have some NAD 27 county boundaries that need to be overlaid against 1988
Tiger
> county boundaries, and they're anywhere from 1/20th of a mile to 1/10th of
a
> mile off depending upon what part of the US I'm looking at.
>
> In Arcview 3.2, there is a projection conversion utility which allows the
datum
> of a projection to be changed. I don't believe Mapinfo has the ability to
> change a datum using the "Save Copy As" command.
>
> Berk Charlton
Pardon me if I go off on a little rant as I answer your question, because
there is a way to do it, but there is a less complicated way that *should*
work but didn't, the last time I tried it.
The surefire way to do this is
- Use table/export to create a MIF/MID file pair of your table
- Use a text editor to change the datum number of the Coordsys clause
in the MIF file
- re-import the edited MIF file.
The way that *I wished* worked would simply be
- use File -> Save As to save your NAD 83 map into a temporary
table, changing the NAD 83 projection to a "Non-Earth" projection.
- Open that table in MapInfo.
- Use "File -> Save as" on the "non-earth" table to save it into the final
table, changing the "non-earth" projection to your NAD 27 projection.
This method presents fewer opportunities for making mistakes, and doesn't
require an outside text editor. If only it worked.
Hope this helps,
Spencer
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