[Proj] NAD conversion test points?

Eric Miller EMiller at dfg.ca.gov
Tue Mar 9 17:50:02 EST 2010


Your confusion might be cleared up by knowing that the "proj" program does not perform any datum conversion.  If your ellipsoid/datum is different between inputs and outputs you should use the "cs2cs" program.  Additionally, with "cs2cs" there is a "nadgrids" argument to specify a specific correction grid.

Furthermore, I assume your nadgrids files were processed with nad2bin on an OSX machine of the same kind (32 or 64 bit).  This is important because cs2cs depends on machine specific binary files.  Probably you'd get a segment violation if that wasn't the case.  It'd be nice if someone wanted to convert it to use the "new" las/los files from the NGS.  But, until then...

Eric G. Miller
Staff Programmer
CA Dept. of Fish & Game

>>> On 3/9/2010 at 11:53 AM, William Kyngesburye <woklist at kyngchaos.com> wrote:
> I'm trying to figure out a 32/64bit problem on OSX with the NAD files, and 
> need some test points.
> I found the example in the cs2cs man page, but it doesn't seem to agree with 
> what I got with NADCON (http://www.ngs.noaa.gov/cgi-bin/nadcon.prl).  From 
> NADCON, for the cs2cs example point -111.5 45.25919444444, I get a NAD83 to 
> NAD27 latlong of 111d29'57.12835"w 45d15'33.35792"n.
> I plug this into proj to get the UTM coordinate (this shouldn't be affected 
> by NAD conversion in proj):
> proj +proj=utm +zone=10 +ellps=GRS80
> 111d29'57.12835"w 45d15'33.35792"n
> 1402259.10	5076507.88
> Not the same as the UTM coord from the cs2cs example:
> cs2cs +proj=latlong +datum=NAD83 +to +proj=utm +zone=10 +datum=NAD27
> -111.5 45.25919444444
> 1402285.99	5076292.42 -0.0
> But, if I use NAD27 in proj on the NADCON latlong, I do get the UTM coord 
> from the example, but this doesn't seem right - like I'm doing the datum 
> conversion twice, once in NADCON latlong NAD83 to latlong NAD27, and once in 
> proj latlong NAD?? to UTM NAD27:
> proj +proj=utm +zone=10 +datum=NAD27
> 111d29'57.12835"w 45d15'33.35792"n
> 1402285.99	5076292.42
> Is this right? does the output datum in proj also set the input latlong 
> datum?
> My own test with cs2cs (which I'm trying to figure out if it's wrong) gives:
> 1402224.58	5076275.42
> Is maybe the cs2cs example wrong for the output?  I did figure out that the 
> lat/long in the example should be switched (x,y order), so maybe something 
> else is missing?
> -----
> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
> http://www.kyngchaos.com/ 
> Earth: "Mostly harmless"
> - revised entry in the HitchHiker's Guide to the Galaxy
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