New OSGB co-ordinate system

[JanineW]

The OSGB has developed a new co-ordinate system and I would like to have it working in AutoCAD Map 3D 2012, 2014 and 2016 (several users).  The new code is OSTN15 (to replace OSTN02).  Is there a way I can import a new co-ordinate system into these versions of Map 3D?  I tried the MAPCSLIBRARYIMPORT command, but it just said 'unknown command'.  I've downloaded the files from the OS and I was hoping somewhere I could just run a command that would do it for me, so I don't have to define a co-ordinate system manually.

The downloaded OS files include 4 pdfs, a .GEM, a .csc and a .DAT

Apparently the change will only make about 11-15mm difference, but I'd like to keep everyone up to date if I can.

Any ideas anyone?

Thanks

Janine

[Pointdump]

Janine,

I heard about this and wondered myself:
http://www.osi.ie/wp-content/uploads/2016/08/OSGM15-and-OSTN15-Updated-transformations-for-UK-and-Ir...

"The downloaded OS files include 4 pdfs, a .GEM, a .csc and a .DAT"

Can you post these, or a link to them? You'll probably need to make a copy of the OSTN02 and re-define and re-name it to OSTN15.

Dave

[JanineW]

Dave,

I've attached the files as a zip file.  I've not re-defined a co-ordinate system before.  Would I just use their files, or would I have to change the data manually?  Apparently the files for Ireland and Northern Ireland have not changed, but the OS have issued new files (I've attached them though I don't need them myself).

Any advice would be gratefully received.

Janine

[Pointdump]

Janine,

This is a little over my head. I think it's not a Coordinate System re-definition, but rather a transformation re-definition involving GSB files. Kinda like the Canadians, Japanese, and Danes went through a couple of years ago. I'm not sure how to proceed. I'll research this. Thanks for posting those files.

Dave

[JanineW]

Dave

Me neither.  I've emailed the OS to try and get a bit of clarification on what (if anything) needs to be done from an AutoCAD perspective.  If it is just the surveying equipment that will be changed, it's not my issue. If it is more than that, I may start to panic.  I'll let you know if I hear anything.

Thanks for your help

Janine

[JanineW]

Dave

What I heard back from the OS regarding OSTN15 is below.  Seems like it is well beyond me and I would need an expert to guide me through it, or someone in Autodesk to release an update including OSTN15, if that is even possible.  I'm still slightly baffled though as it isn't a co-ordinate system.  My head hurts just thinking about it. 

Janine

Two changes were implemented to OS coordinate systems on Friday.

Our technical document “A guide to coordinate systems in Great Britain” has also been updated - https://www.ordnancesurvey.co.uk/docs/support/guide-coordinate-systems-great-britain.pdf.

The two changes were:

1. The coordinates of all the stations in the OS Net network (that supplies RINEX data) were updated to an improved realisation of the ETRS89 coordinate frame.  The change between the old (“v2001”) OS Net coordinates and new (“v2009”) is generally small (about 15mm RMS). 
2. OSTN02/OSGM02 was updated to OSTN15/OSGM15.  The changes in OSTN02/15 (the horizontal transformation) are small.  The changes in OSGM02/15 (the height transformation) are larger due to improvements in the underlying gravity model and also improvements in its fit to the mean sea level datums.

To gain the best accuracy from OS Net RINEX data used from now on it would be best to employ OSTN15 in your survey equipment and AutoCAD.  Regarding survey kit the antenna phase centre offsets that go with OS Net station RINEX data have also been updated. Details of the offsets to now use with OS Net RINEX are here - https://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-n...

OSTN15 and OSGM15 are not really coordinate systems that can be described by a few parameters but complex transformations between systems.  OSTN15 links ETRS89/WGS84 with the legacy OSGB36 mapping system and OSGM15 links heights from ETRS89/WGS84 with legacy heights related to mean sea level Ordnance Datum Newlyn (ODN) and other datums used on e.g. Scottish Islands.  Both OSTN15 and OSGM15 (and the 02 version) are grids of transformation parameters at 1km density and 700km x 1250km size so that’s over 2.6 million parameters (dE, dN, dH).

I know nothing about setting up AutoCAD I am afraid but I assume that if you had OSTN02/OSGM02 in it you need to replicate the use of the OSTN02/OSGM02 parameter file with that for OSTN15/OSGM15.  The OSTN15/OSGM15 parameter file is exactly the same format as that for OSTN02/OSGM02 and is available here - https://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-n....  All other parameters such as the defining constants for ETRS89 and OSGB36 are unchanged and the transformation algorithm is unchanged also.  Technical details of how the transformation is implemented are in the guide contained in the developer’s pack.

Looking at your screen grabs I ASSUME that OSTN02 was introduced to AutoCAD using the raw data file because of the ‘Source’ reference in the first screen grab – “Transformations and OSGM02 User Guide”.  So, my GUESS is that you will need the OSTN15 developers pack referenced above (and the new guide contained therein).  I would hope that some in Autodesk could help with this since it’s clearly been done before for OSTN02.

[Pointdump]

Janine,

This is definitely a support issue. Are you on subsciption?

In Windows Explorer, search for "Geospatial Coordinate Systems". You should see at least one folder with a number like 14.00. (That number represents year/version)

Open that folder and you'll see OSTN97 and OSTN02 files.

I'm thinking that all you need to do is drag-n-drop the new OSTN15 files in here and you're golden. But I really think some guidance from Autodesk would be prudent.

Dave

[JanineW]

Dave,

We don't have a subscription unfortunately.  I'm going to have to rely on the goodwill of other users on the forum 🙂

Thanks very much for your help

Janine

[Pointdump]

Janine,

Oh, and the OSGM15 won't be used because AutoCAD cares nothing for Vertical Datums. So just OSTN15 needs to be dealt with.

Dave

[JanineW]

Dave,

I tried drag and drop, but that hasn't worked.  It looks like they might be the wrong filetype.  I've got .asc and .gsb, but the Geospatial Coordinate Systems folder contains .csd,  .gdc and .mrt

Wish my boss had bought a subscription with support.

Janine

[Pointdump]

Janine,

"...might be the wrong filetype. I've got .asc and .gsb, but the Geospatial Coordinate Systems folder contains .csd, .gdc and .mrt"

Yes, I wondered about that too. Here's how the Canadians dealt with their new version of NAD83:
http://blogs.rand.com/civil/2013/10/imaginit-utilities-for-civil-3d-coordinate-systems.html

I'm going to head over to the ESRI Forum (I think ESRI has a forum) and see how they're dealing with this.

Dave

[JanineW]

Dave,

I've tried the method you just sent, but it is a different set of menus for OSTN02.  I made a duplicate hoping I could edit it from there, but there is no menu option to add the .gsb file.

Surely someone somewhere knows how to do this, it can't just be us trying to work it out?

Thanks for all your help with this.

Janine

[Pointdump]

Janine,

"Surely someone somewhere knows how to do this, it can't just be us trying to work it out?"

Doesn't it just seem that way sometimes? And you would think that Autodesk would be all over this, offering hotfixes or step-by-step instructions. Instead, crickets........

I wasn't able to find an ESRI Forum. I can't believe they don't have one!

Dave

[JanineW]

Dave

For now I'm just going to have to leave things as they are and hope there are no serious issues.  I'll keep checking and hope that someone figures it out.  When my boss gets back tomorrow I'll check if we have support for any of the newer versions of Map 3D and see if I can get any help that way. If I find anything out, I'll post back and share the 'knowledge' 🙂

Good luck

Janine

[neilyj666]

I'm in the UK and have a subscription so will be affected by this so I'll raise a support ticket and see what happens.....!!!

EDIT: Ticket raised 08:41 01/09/16

[JanineW]

Neilyj

That would be fantastic. Thanks.

I'm really surprised that this hasn't been picked up by more people.  Maybe we're concerned about nothing, but it would be nice to know.

Cheers

Janine

[neilyj666]

No problem - although I wouldn't hold my breath waiting for a solution from Autodesk.....:)

[Pointdump]

Thank you Neil. Yes, it's best to keep breathing while we wait.

The more I read about OSTN15 the more I'm just not grasping the key concepts. Is it a Datum Realization or a Projection?

If it's just a new projection, we should be able to edit a copy of the OSGB-GPS-2002 Projection and voila. But I can't figure out what to edit.

Dave

[neilyj666]

All this coordinate transformation stuff is a bit of a Black Art IMHO.....

[Pointdump]

Neil,

"Bit of a Black Art" indeed! My head hurts from trying to understand this.

OK, so from <<<This website>>> I found a potential nugget of information:

"Back in the 1930’s, the UK Ordnance Survey defined ‘OSGB-36’ as the datum for the UK, based on the ‘Airy 1830’ ellipsoid. In 2014, they deprecated OSGB-36 in favour of WGS-84 for latitude/longitude coordinates, but OSGB-36 is still the basis for OS grid references. The Greenwich Observatory – historically the ‘prime meridian’ – is around 000°00′05″W on the WGS-84 datum (a difference of a bit over 100 metres): and moving every year. (I find the history of cartography facinating: I will put together a reading list sometime).

So to convert a (WGS84) latitude/longitude point to an OS grid reference, it must first be converted from the WGS84 datum to the OSGB36 datum, then have the transverse Mercator projection applied to transform it from a curved surface to a flat one."

If that is true, then is OSTN15 the transformation between the WGS84 Datum and the OSGB36 Datum? That makes sense, and would explain why things changed from 1997 to 2002 to 2015, but I still don't know what to do with it.

Dave