Inaccuracy of ACAD linked import

Problems, issues, and concerns... Oh my!
Not for "I don't know how", but for "Revit says this but doesn't do it..."

Moderators: Tim Waldock, Andrew Munoz, simonwhnz

Inaccuracy of ACAD linked import

Postby monumentum » 27 Aug 2007, 13:23

Has anyone seen an issue like that shown in the attached screen shot. My Revit window is on the left and ACAD on the right.

The Revit window shows a linked import of the ACAD drawings shown on the right.

If you look closely you'll notice that the (magenta) boundary line is slightly different in the linked import in Revit. It is actually out by 25.2mm.

The linked files use a consitent "nearby" origin, etc.

Any leads would be greatly appreciated!

GC
Attachments
BDY LINE ANOMOLY_070827.jpg
GCC @ Monumentum
User avatar
monumentum
Moderator
 
Posts: 35
Joined: 30 Apr 2006, 22:00
Location: Sydney

Postby D'zinner » 27 Aug 2007, 14:31

Ive had the same problem when linking a cad survey to use as any underlay, when zooming & panning, lines from the imported cad drawing jump around and move. This has only happened with two jobs, making me think, this an issue with the cad file, more than a revit problem.
'Only when the last tree has withered,
the last fish has been caught,
and the last river has been poisoned,
will you realize you cannot eat money.'
Native American proverb
User avatar
D'zinner
Active member
 
Posts: 60
Joined: 24 Feb 2007, 22:11
Location: Bunbury, WA

Postby monumentum » 27 Aug 2007, 15:16

Well... The explanation from "Cadgroup" suggested that somehow the Revit project database has become corrupt.

Interestingly enough, when I created new layers in the ACAD dwg and transferred the lines to the new layer, and reloaded the dwg... all is good!

But of course the damage is already done as the project has been modeled to the "slightly" incorrect alignment!

Anyhow, Cadgroup are going to forward it on to Autodesk for an autopsy... It will be interesting to see if they come up with anything useful!

GC
GCC @ Monumentum
User avatar
monumentum
Moderator
 
Posts: 35
Joined: 30 Apr 2006, 22:00
Location: Sydney

Postby J S Shelton » 28 Aug 2007, 00:07

Wierd!

What's the screen shot of by the way? A 2D plan? A property?
J S Shelton
 

Postby monumentum » 28 Aug 2007, 10:15

Weird indeed!

The magenta lines from the screen shot are actually property boundary lines from an AutoCAD survey.

The other lines are walls, fences etc... But all the lines you see are from linked AutoCAD imports... No Revit elements at all!

Interestingly enough, if I import the faulty DWG into a fresh Revit project there is no problem!

So Cadgroups basic explanation would seem to be on the money. But it remains a bit of a concern that this could happen!
GCC @ Monumentum
User avatar
monumentum
Moderator
 
Posts: 35
Joined: 30 Apr 2006, 22:00
Location: Sydney

Postby D'zinner » 29 Aug 2007, 17:17

Thats very interesting monumentum, was it a survey drawing you were importing?
This problem has only ever happened to me when importing a cad survey, I worked out the problem for me was beacuse the survey was using z-coordinates, I reloaded the survey again, as a flat drawing and it worked fine. All other cad imports have been 100% acurate
'Only when the last tree has withered,
the last fish has been caught,
and the last river has been poisoned,
will you realize you cannot eat money.'
Native American proverb
User avatar
D'zinner
Active member
 
Posts: 60
Joined: 24 Feb 2007, 22:11
Location: Bunbury, WA

Postby monumentum » 29 Aug 2007, 20:13

Yes... The linework was in fact originally from a survey drawing. However, for better or worse, we always extract the info from the original survey into a new dwg. We endevour to ensure, as far we're aware, that the dwg contains 2D info only! Something may have slipped through the net this time... Although I'm not sure what!

I still haven't heard anything back from Autodesk! Strangely enough!
GCC @ Monumentum
User avatar
monumentum
Moderator
 
Posts: 35
Joined: 30 Apr 2006, 22:00
Location: Sydney

Postby Roberto Pachon » 09 Nov 2007, 16:16

Monumentum, survey drawings are usually the main cause for drawings to behave strangely.

As a rule, I leave the survey drawing untouched in an "Import" folder, then make a copy to be used in the project and CLEAN IT UP.
This process usually involves "flattening", purging and auditing the drawing.

Regarding the linked DWGs, I recently worked on a project with a linked lot subdivision DWG.
Later, I was required to export the layout from Revit as DWG.

I placed this exported DWG into the original Lot Sudivision that was linked into Revit and guess what. The exported DWG didn't match the original DWG that was linked into Revit.

It was off slightly everywhere and not by a consistent margin.

My conclusion is that the round trip of DWGs is not 100% accurate.
Roberto Pachon
B.Arch MDesSc (Comp)
Roberto Pachon
Active member
 
Posts: 60
Joined: 08 May 2006, 16:11
Location: Sydney, AUSTRALIA
Real Name: Roberto Pachon
Company: Lateral Estate
When did you start to use Revit?: v5.1 2003

Postby D'zinner » 12 Nov 2007, 10:43

Here is a great little Autocad lsp, to flattern drawings using Z - Co-ordinate Flattern.lsp
Attachments
Flatten.zip
(3.72 KiB) Downloaded 356 times
'Only when the last tree has withered,
the last fish has been caught,
and the last river has been poisoned,
will you realize you cannot eat money.'
Native American proverb
User avatar
D'zinner
Active member
 
Posts: 60
Joined: 24 Feb 2007, 22:11
Location: Bunbury, WA

DWG vs REVIT inaccuracies

Postby chrisneedham » 16 Nov 2007, 11:53

I've seen this issue before, and in my experience, it doesn't have anything to do with the survey file itself, other than it is usually provided in METRES. If you scale up the drawing from its origin (by a scale factor of 1000), and then import it into Revit, this display issue should disappear.

Of course, you should still flatten, audit, purge etc. for other reasons.

Hope this helps,
Last edited by chrisneedham on 16 Nov 2007, 12:33, edited 1 time in total.
Regards,

Chris Needham
C3 Consulting Solutions
www.c3consulting.com.au

REVIC Chairperson
www.revic.org.au
chrisneedham
Active member
 
Posts: 16
Joined: 14 Aug 2007, 10:26
Location: Melbourne

Postby Roberto Pachon » 16 Nov 2007, 12:20

Chris is right. One of the necessary steps in "cleaning up" the surveyors drawings includes scaling it up by 1000 from 0,0 so it's in the same units
(mm) as your Revit drawing.
If possible, move the survey close to 0,0

This would save you a few headaches down the track.
Roberto Pachon
B.Arch MDesSc (Comp)
Roberto Pachon
Active member
 
Posts: 60
Joined: 08 May 2006, 16:11
Location: Sydney, AUSTRALIA
Real Name: Roberto Pachon
Company: Lateral Estate
When did you start to use Revit?: v5.1 2003

Moving surveys

Postby chrisneedham » 16 Nov 2007, 12:32

If you do move the survey, define a point within the survey file and record the coordinates. In effect, this becomes a 'local' datum, which, when used, will permit Shared Coordinates to be used.

Beware also the UCS created in the DWG file(s) when you publish coordinates from Revit, as I believe it is created 'backwards'. I've used lisp files in the past for an inbound and outbound conversion, where the UCS is reversed, and the entire contents of the file are moved from one datum to the other. It works, but it's still a pain and should not be required if/when Autodesk sorts this issue out once and for all.

Alternatively, you can use acquire coordinates and specify project coordinates, but I've found inconsistencies in this process, and am still nutting it out to suit all occasions. Ask me later, or let me know what tips you have that I may have missed...
Regards,

Chris Needham
C3 Consulting Solutions
www.c3consulting.com.au

REVIC Chairperson
www.revic.org.au
chrisneedham
Active member
 
Posts: 16
Joined: 14 Aug 2007, 10:26
Location: Melbourne

Postby David Howe » 30 Nov 2007, 14:41

Revit needs to be updated to use 64 bit floating point numbers for ordinates or we will continue to experience problems when importing from AutoCAD (which has used 64 bit ordinates since its inception). Refer to the following article:

http://www.intelcad.com/pages/autocad/
David Howe
Active member
 
Posts: 62
Joined: 01 May 2006, 09:47
Location: Sydney
Real Name: David Howe
Company: Edge Condition
When did you start to use Revit?: v3.1 2001

64 bit floating point numbers

Postby chrisneedham » 13 May 2008, 19:12

Conjecture, perhaps, but I heard that the problems are OpenGL (display) related - not so much mathematical in regards to the internal calculations... This would perhaps indicate why AutoCAD doesn't suffer from the same problem, and why Revit still does. I'm not suggesting that OpenGL is not the right choice, either. I know only enough about it to know there are a lot of gray areas (pun intended), regarding OpenGL standards and versions. Similarly I don't know that support for DirectX is automatically a solution, either.

I also understand that it is because of OpenGL limitations that dual screen support is not yet implemented, as the two are closely linked. :shock:
Regards,

Chris Needham
C3 Consulting Solutions
www.c3consulting.com.au

REVIC Chairperson
www.revic.org.au
chrisneedham
Active member
 
Posts: 16
Joined: 14 Aug 2007, 10:26
Location: Melbourne

Postby David Howe » 16 May 2008, 15:59

You are kidding right????
David Howe
Active member
 
Posts: 62
Joined: 01 May 2006, 09:47
Location: Sydney
Real Name: David Howe
Company: Edge Condition
When did you start to use Revit?: v3.1 2001

Next

Return to Buglist

Who is online

Users browsing this forum: No registered users and 1 guest

cron