Lat Long Conversion in Civil 3D Not Correct

[musasalemi]

Hi All!

I was tried to convert a point from UTM-39N to Lat/Long using geodetic calculator; but when I checked the converted coordinates by another applications (like GeoLab); they were a little different (about two seconds) & I'm sure GeoLab is right. Any Help?

My settings and other information is attached.

Sorry for poor English

Thank you.

[antoniovinci]

Try another way: first _MAPEXPORT it to a point shapefile in LL84, then _MAPIMPORT it back to check the precision.

[musasalemi]

thanks, but unfortunately it doesn't work.
my question is why this had happened?

[antoniovinci]

Please attach that UTM-39N point in DWG format, and paste here the expected LL84 coords, thanks.

[musasalemi]

Expected latitude and longitude is:

 Lat: N27° 29' 53.196774"

 Long: E52° 38' 17.028054"

and what Civil3D give me is:

 Lat: N27° 29' 51.8162"
 Long: : E52° 38' 16.7578"

and the drawing that have the point is attached (Civil 3D 2012).

 thanks.

[antoniovinci]

Well, I tried to convert your EPSG:2059 point (X = 661811.296 , Y = 3042675.664) to EPSG:4326 (i.e. Lat-Long datum WGS84) with two different softwares, and here are my results.

1] Quantum Gis yields
LONG = 52.63811871
LAT = 27.49647281

2] Autocad Map2006 yields
LONG = 52.63815850 
LAT = 27.49648261

then I calculated the HH'MM'SS' format here: http://www.earthpoint.us/Convert.aspx 

The Qgis coords are: 27°29'47.3021", 052°38'17.2274"

The Autocad coords are: 27°29'47.3374", 052°38'17.3706"

As you can see, there's a LONG difference of 0.1432" and a LAT of 0.0353, yielding a 4 meters shift in LONG, and 1 meter in LAT.

Since two dfferent tools gave an almost identical result, I guess your expected coords Lat: N27° 29' 53.196774" Long: E52° 38' 17.028054" are simply wrong, sir.

[musasalemi]

I work in an oil and gas company and I almost always have to convert Bench marks coords to lat/long or from lat/long coords. because of my job, the converted coords must have high accuracy (often 3mm) and when I use Geolab, I get this precision. I used to check Geolab with a high accuracy routine in MATLAB; so I trust Geolab.

Any Idea?

Thanks.

[Sinc]

A pipeline must be within 3mm of accuracy horizontally...?  Wow.  Seems like major overkill to me.

[musasalemi]

Yes! I think pipe supports and their bolts, pipe equipments like boilers and etc. need that precision.
However I said I want that accuracy for the Bench marks!

[907Trekker · Accepted solution]

Everybody is correct!

The problem is we are using different horizontal datums, in your autocad image you used the European Datum, but in the GeoLab you used WGS84.  I'm not sure what other people are using.  To check AutoCAD against GeoLab I used WGS84, the same that you used in GeoLab and the resultant coordinates matched, see below:

I STRONGLY suggest that you confirm what datum you are using.  People not understanding horizontal (and vertical) datums can lead to very costly mistakes. 

As a PLS this is always something I fear, when people start converting coordinates I start getting phone calls at 2 in the morning.  I suggest you talk to your surveyor about your projects coordinate system, I'm sure they will tell you the same.

Thanks,
Mark

[musasalemi]

This is it! Thank you very much.

[antoniovinci]

I beg your pardon, mr.Musasalemi.

I was misled by your TEST.DWG which contains an incorrect _ADESETCRDSYS value, referring to the wrong datum...

[musasalemi]

Oh! that's OK. Never mind.