C3D-XREF COORDINATE TRANSFORMATION

[CADEngr2014]

Hello,

I am using C3D 2014.

I have an xref file at one coordinate system and xrefed into a file with another coordinate system.  Does the xref perform a coordinate transformation thru its referencing functionality..

[Jay_B · Accepted solution]

For a true transformation, the files need to be transformed separately.

There are a couple of other options such as attaching the xref as is & rotating, scaling etc. (but will only be so close and common control points are needed etc.)

There's also the "Locate Using Geographic Data" option within the External reference dialog which requires the GEOMARKERVISIBILITY sys. variable to be set to 1 AFAIK.

I highly recommend verifying the results if using this method.

[darreng_oa]

i just had a real bad experience with using the option of "Locate Using Geographic Data" as i tried to attach a dwg in a different coordinate system.  C3D help came up with this from the very clear warning it gave me as i hit OK: 

"If the GIS coordinate systems are not the same, only the geographic marker transforms correctly to the host drawing’s GIS coordinate system. The other points may not transform correctly and may indicate incorrect geographic locations. Hence, the system warns you if it detects a coordinate system mismatch when you attach or insert the drawing. It however does not prevent you from attaching or inserting it."

the reference i wish to convert is in a state plane system - meters, and my desired units are the same state plane zone, but in feet.  really not sure what C3D did, and it got close - only about 4.5' off, but i am glad i am old school enough that i have always converted coordinates using NADCON (corpscon 6) and noticed the difference.

i obviously do not understand transformations well enough, but is it not suprising that attaching a reference using geographic data would really be this far off from NADCON?

any ideas?

thanks!  Darren

[Pointdump]

Darren,

4.5 Feet? That sounds suspiciously like a US Survey Foot/International Foot thing.

Dave

[darreng_oa]

thank you for the quick reply

(ive included a screen shot)

the linework i received is very simple, consisting of 6 closed polylines each outlining different small areas in a marsh each approximately 500' x 200' over an area of a mile or so. the Units and Zone for the dwg with the linework were set to the correct state plane zone (as well as projection and datum),  in meters, and the Imperial to Metric conversion set to International Foot.  The Transformation tab is also populated with a reference point.

to veryify my xref attachment, i simply extracted the XY for the vertices of all these polylines in meters, converted the points separately in NADCON, then inserted the newly generated points list, and as i described, this is where i noticed a static offset.  Actually, under closer inspection the distance is a constant 13.73 feet shift at 200deg (sorry, i screwed up my distance tool in the ealier post!)

i used to think that the intl/US foot only applied a great distances? Do you still feel this a unit issue?

regards, darren

[Pointdump]

Darren,

The difference between Survey Feet and International Feet is 2PPM. Take one of your point coordinates and multiply both the Northing and Easting by 0.000002. If the distance from the multiplied point to the original is 13.73 feet, then you know what the problem is.

Dave

[darreng_oa]

A+

that was exactly the problem.  i recomputed the points to using intl foot, and voila

thank you for time and patience

[darreng_oa]

if i may ask a follow up question and review of procedure:

i am not sure where in the process the translation bw intl foot and US foot is getting applied. For example, the dwg i recieved with the linework, was in a local state plane - meters, so when i attach that file using geo location data to a dwg that set in feet, its the Imperial to Metric Conversion setting of my NATIVE drawing that controls the transformation or is the settings of the xref dwg?

thanks!

[Pointdump]

Darren,

Like Jay said up above:

"For a true transformation, the files need to be transformed separately."

I'm still trying myself to figure out how to transform an Xref with a different coordinate system into a drawing with the desired coordinate system. I've had mixed results. Check this out:
https://www.youtube.com/watch?v=cKv7wYW7-Fc

Dave

[Pointdump]

Darren,

OK, I think I've got it sorted out.

A key concept in transformations between drawings is to Assign a Coordinate System, to each drawing, in Planning and Analysis (Map Workspace), even if you have already assigned a coordinate system in the Units and Zone Tab of Drawing Settings in the Civil 3D Workspace. You can then Query in AutoCAD stuff like Linework. You cannot Query in COGO Points or Civil 3D Objects.

If you want to Xref in a drawing from another coordinate system, you'll first have to transform one or the other so that both drawings match. When you bring the Xref in, you'll be able to see the C3D Objects, but the Objects won't be in the Prospector Tab. You'll have to Import or XML any Points or C3D Objects.

Dave

[Anonymous]

Dave, This is an old thread. Is it still accurate with respect to Civil3D objects such as alignments and surfaces, that they basically can't be directly shared across differing coordinate systems?

Kev