[Proj] NAD 27 v 83 Distances

Frank Warmerdam warmerdam at pobox.com
Fri Oct 1 11:28:25 EST 2010

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.


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, warmerdam at pobox.com
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