Civil 3D not supporting OSTN15 & OSGM15

[Anonymous]

Civil 3D is one of the leading survey & construction software and is feature packed and priced accordingly. However how come this pricey market leading software doesn’t support a three year old transformation & geoid models?

How do UK civil engineers cope with this, or is it a case of the UK surveyors who utilise Civil 3D having to remain on OSTN02/OSGM02 & is this acceptable?

Please let me know as I’m concerned over the accuracy that I’m producing, using an out of date model when surveying.

Thanks

[Pointdump]

Ian,

OSTN15 was discussed >>>Here<<< in the Map3D Forum. You can add it yourself to MAPCSLIBRARY, but the biggest challenge is understanding exactly what OSTN15 is. I read everything from OS about it, but the more I read the more confused I got. Finally had to give up.
OS has posted the necessary NTv2 files >>>Here<<<.
Dave

[Anonymous]

Thanks Dave, I've reviewed the links you kindly included..

It appears that not that many users are really concerned that Civil3D doesn't have the OSTN15/OsGM15 template. So maybe I'm worrying over something that I shouldn't be, with the accuracy of my topos taken with the OSTN02 settings?

I'm not comfortable manipulating setting myself in case I do introduce an issue.

If the civil engineering surveyors who work in the transport / rail industry (where mm accuracy is required) are not that worried, then I shouldn't be either... I guess! 

Cheers

Ian  

[Pointdump · Accepted solution]

Ian,
I'm re-reading OS's Guide to Coordinate Systems in Great Britain, which I've attached. It starts off with a really good explanation of Geodetic Terms. Put on a pot of coffee, or tea, and dig in.
I kinda grasp the OSTN15 Concepts, but I don't know how to apply them to C3D's MAPCSLIBRARY. I thought if I looked at how C3D dealt with OSTN02 I could figure things out. I puzzled until my puzzler was sore.
Anyway, I came across this on Page 29:
"In 2002 the definition of OSGB36 underwent a fundamental change with the release of the
Definitive Transformation OSTN02™. OSTN02 was updated in August 2016 to OSTN15. OSTN15, in
combination with the ETRS89 coordinates of the OS Net stations, rather than the fixed
triangulation network, now define the National Grid. This is a subtle change in definition only and
does not mean that existing OSGB36 coordinates need to be changed in any way."
Dave

[Anonymous]

Dave, you are a superstar!

Thanks for taking the 'pain' for me and reading the detail. I bet it's nice and sunny where you are, it's raining 'Cats & Dogs' in the UK at the moment.
You're been very generous with your time, and I can sleep better now.

Cheers

Ian

[Pointdump]

Ian,
OK, I dug in HARD and re-read everything I could find on OSTN15. From OS:
"OSTN15...provides a fit between the GNSS coordinate system European Terrestrial Reference System 1989 (ETRS89) and the OSGB36 National Grid."
OSTN15 is not a Coordinate System. It is a Geodetic Transformation between the Datums used by ETRS89(GRS80 Ellipsoid) and OSGB36(Airy30 Ellipsoid). The only time you might need this is if you want to use high-accuracy GNSS Survey Data in conjuction with the OS Net Base Stations, which use ETRS89.

To add the OSGBtoETRS and ETRStoOSGB Geodetic Transformations to MAPCSLIBRARY, watch >>>This<<<. However, that's not the end of the story. OS provides 4 point lists, input and output, to test. I was off almost a Meter. I found that some of Map3D's Coordinate System definitions were wrong, like their ETRS89 Datum was actually ETRF89, a realization and not a Datum. So I re-defined the Coordinate Systems and Datums of both ETRS89 and OSGB36. Then after adding the GSB files everything worked fine. Whew!
So I think this is the reason why Autodesk hasn't yet included OSTN15 to MAPCSLIBRARY in 2018. (I don't have 2019 to check.)
Dave

[Pointdump]

Ian,

I just learned from @JanineW over in the >>>Map 3D Forum<<< that Autodesk added the OSTN15 transformation in 2019.

Dave

[Anonymous]

Thanks Dave, I'll take a look.

Cheers