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<div> <font size="2" color="black"><pre style="font-size: 9pt;"><tt>>The difference of distances should be modest between the two datums, with of
>course the NAD83 distances being the better of the two. </tt></pre></font>
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Why would NAD83 be the better of the two?<br>
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Regards,<br>
— daan Strebe<br>
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<div style="font-family: helvetica,arial; font-size: 10pt; color: black;">-----Original Message-----<br>
From: Frank Warmerdam <warmerdam@pobox.com><br>
To: PROJ.4 and general Projections Discussions <proj@lists.maptools.org><br>
Sent: Fri, Oct 1, 2010 9:28 am<br>
Subject: Re: [Proj] NAD 27 v 83 Distances<br>
<br>
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<pre style="font-size: 9pt;"><tt>Robert McFaul wrote:
> Hi,
>
> I'm concerned about whether ground surface distances are different between
> NAD27 and NAD83. I'm in California (southern) and thinking about a
> conversion
> of a project to NAD83. I have some cross section distances measured (1000 to
> 3000 feet in length) and suddenly am wondering what sort of differences
> might
> be involved by this change in systems.
Robert,
The difference of distances should be modest between the two datums, with of
course the NAD83 distances being the better of the two. I did a test for a
random point in southern california and the change is datum shift deltas over
one kilometer was about 1cm. You can do similar tests for any area of interest:
cs2cs -f '%.4f' +proj=utm +zone=11 +datum=NAD27 +to +proj=utm +zone=11
+datum=NAD83
440000 3750000
439919.4833 3750196.3019 0.0000
440000 3751000
439919.4784 3751196.3100 0.0000
Best regards,
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, <a href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a>
light and sound - activate the windows | <a href="http://pobox.com/%7Ewarmerdam" target="_blank">http://pobox.com/~warmerdam</a>
and watch the world go round - Rush | Geospatial Programmer for Rent
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</tt></pre>
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