[Proj] Proj4js EPSG:4326 to EPSG:26786 (SP NAD27) 100+ feet Off
Mikael.Rittri at carmenta.com
Sat Oct 15 12:50:36 EST 2011
I think Proj4js supports a +towgs84 argument.
If so, you can replace +datum=NAD27 by an appropiate +towgs84, the problem is just that the published 3- or 7-parameter datum shifts for NAD27 give poor accuracy.
The best one in EPSG is +towgs84=-9,161,179 intended for CONUS east of Mississippi river,
but its accuracy is 11 m (one sigma).
On your test point, it is wrong by 38.3 ft (11.7 m).
So, I tried to construct a better 3-parameter datum shift for Massachussets.
Based on one point in Worcester, I got the result +towgs84=-5.16,143.64,208.44.
When I then tried your example, I got
which is just 5.3 feet wrong.
Of course, my three parameters are not the optimal +towgs84 values for Massachussets NAD27,
and I don't know their accuracy in general, but I hope they can be of some use.
15 okt 2011 kl. 14:48 skrev "Scott DeHainaut" <scottdehainaut at comcast.net>:
> Frank - Thanks for the quick reply! I was afraid of something like that...
> -Scott DeHainaut
> View this message in context: http://osgeo-org.1803224.n2.nabble.com/Proj4js-EPSG-4326-to-EPSG-26786-SP-NAD27-100-feet-Off-tp6894605p6895453.html
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