What to do with multiple alternatives geodetic transformation?

[claudio.ruschel]

In Brazil, we have lots of legacy data that uses South American 1969 datum (SAD69).

The brazilian official agency for geographic issues (IBGE) had been defined some transformation methods to SIRGAS 2000 (equivalent to WGS 84).

The parameters that comes with Autodesk software (even in 2015 version) are deprecated.

So, I had to define new coordinate systems, datum, ellipsoid and geodetic transformation.

I made some tests and noticed that using DWG transformation through "Attach Drawing" and "Define Query", if I have more than one geodetic transformation alternative (ex: analytical formula-IBGE2005 vs grid interpolation-IBGE2010), the software takes one of these, but don´t ask the user and even do not report the user which one had been used to perform the transformation.

1 - Is there a detailed log file that documents the transformation performed? The only log that is shown is when a feature error is found, but it is useless, since it don´t explain the trouble found.

2 - Since the user cannot choose a specific transformation, which is the criteria used by the software to choose the transformation?

3 - How could I contribute with Autodesk to include these brazilian official definitions in the next software patch?

[diane.cloutier]

Hello Claudio,

One of our Brazillian Application Engineers recommended the following video, which offers a solution to the error with the SIRGAS 2000 Coordinate system definition in AutoCAD Map 3D and Civil 3D:

https://www.youtube.com/watch?v=pDA5zrAfPAw

Please let us know if this helps.

Thanks,

[diane.cloutier]

Hi again,

I wanted to let you know that I just logged the issue with our development team and it is now being tracked under DE20059.  Also, if you would like to submit any feedback of your own to the Product Manager, you may do so through the following link:

http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=1109794

Thanks,

[claudio.ruschel]

This solutions consider the default SAD69 AutoCAD Map definition.

This definition is not the same that IBGE defined to use, since IBGE defines the "EPSG 7050 - GRS 1967 Modified".

So, to implement it, like Resolution RPR 01/05, it is needed to define 4 new elements:

- Elipsoid

- Datum

- Coordinate System

- Geodetic Transformation

The attached file contains a sample of such files using UTM 22 S

So, you must assign a user defined coordinate system in order to perform the adequate transformation.

I tested this definitions and got the same results that ArcGIS produced with this transformation:

Source: SAD_1969_UTM_Zone_22S (WKID: 29192 Authority: EPSG)

Target: SIRGAS_2000_UTM_Zone_22S (WKID: 31982 Authority: EPSG)

Transformation: SAD_1969_To_SIRGAS_2000_1 (Geocentric Translation – dx=-67,35  dy=3,88  dz=-38,22)

This file must be unzipped and installed at:

( http://knowledge.autodesk.com/support/autocad-map-3d/troubleshooting/caas/sfdcarticles/sfdcarticles/... )

• Source folder (pre-2014 release) - copy all *.CSD files in %PROGRAMDATA%\Autodesk\Geospatial Coordinate Systems
• Target folder (post-2014 release) - paste files into "%LOCALAPPDATA%\Autodesk\User Geospatial Coordinate Systems

[claudio.ruschel]

I noticed an error when trying to assign the user coordinate system that I created to a drawing:

"Cannot save projection code to the drawing."

That´s why I did not included a Geodetic Transformation Path to WGS84, as required:

http://knowledge.autodesk.com/support/autocad-civil-3d/troubleshooting/caas/sfdcarticles/sfdcarticle...

In the attached file, I included this required "geodetic transformation path".