Bill,
I recommend you try the Geod software recommended by John Elliot first. If that fails
you might want to adapt the procedure I used for similar conversion from AGD84.
Apparently, there is a projection definition issue associated with MapInfo's version
of the AGD84 projections. This issue was resolved in the conversion process below, by
editing the mif file. You would have to determine whether this process works for your
specific projection.
PROCEDURE :
Convert tables with projection of
Category = ISG (AGD84), Member = ISG Zone56.1,
to projection of
Category = Map Grid of Australia 1994 (MGA94), Member = MGA Zone56 (GDA94)
- open table in mapinfo
- export to mid/mif format as "xxx"
- "close all" in mapinfo
- open xxx.mif in wordpad
- change "13" to "12"
- save and exit from wordpad
- import xxx back into mapinfo as "yyy"
- open yyy and check projection is:- Category: Australian State Grids, Member: NSW
Integrated Survey Grid (ISG) Zone 56/1 (Note that this projection is based on AGD66)
- save copy of table as "zzz", specifying a projection of GDA94, MGA Zone 56.
- "zzz" is the final product
Regards
Tom Colley
Sustainability Systems Analyst
Blue Mountains City Council
Tel: (61.2) 4780-5451
[EMAIL PROTECTED]
-------- Original Message ----------------------
Date: Thu, 18 Dec 2003 18:04:18 +1100
To: "Data Directions" <[EMAIL PROTECTED]>,
<[EMAIL PROTECTED]>
From: "John Elliot" <[EMAIL PROTECTED]>
Subject: Re: MI-L Australian GDA94 projection issues
Message-ID: <[EMAIL PROTECTED]>
Try the Geod software from NSW Dept Lands - it is free and was designed
precisely for the job you have in mind.
http://www.lpi.nsw.gov.au
John
----------------------------------
John Elliot
Anzeco Pty. Limited
mineral exploration consulting services
Bathurst, NSW 2795, AUSTRALIA
Email: [EMAIL PROTECTED]
----- Original Message -----
From: "Data Directions" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: 18 December, 2003 3:11 PM
Subject: MI-L Australian GDA94 projection issues
I have been having all sorts of problems with converting Australian
projections between AGD84 and GDA94, both as spherical and cartesian
coordinates.
I have MapInfo data in AGD84. I go through the conversion process to GDA94
using various methods (FME some time ago, and now via ESRI ArcTools) and end
up with a dataset projected in GDA94. However, when I overlay this data with
the original AGD84 data, there is only about a 3 metre offset, not the 200
metre offset that it should be.
But if during the conversion process, I set the coordinate system to GDA94
again, and then overlay the original GDA94 data with the converted data,
there is the 200 metre (or so offset).
In a nutshell, my processing steps are:
1.. From MapInfo, export the source AGD84 table as MID/MIF format.
2.. In ArcToolBox, convert the MIF to a Shapefile, assign the source
projection (AGD84) and then specify the projection going to (GDA94).
3.. Go back to MapInfo (v7.5) and import the Shapefile, selecting GDA94 as
the projection. This results in only a 3 metre offset. But at this stage, if
I import the Shapefile and select AGD84 (the original projection), the 200
metre offset is apparent.
Are there any ideas what is going on? Will sum.
Many thanks,
Bill
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