Friday, May 30, 2014

Insert using Auto-Center to Center

Whenever we insert a linked file we find that Revit is wired or biased to using Auto-Center to Center. It doesn't matter if we've just used another placement option Revit faithfully returns to its favorite.

The reason for this preference or bias stems from the reality that DWG files are a perfect storm of chaos that we cannot reliably expect that the elements in the file are located near the origin of the file. Floating Point math calculations rely on constraining the size of the world we work in to a practical scope so that calculations can be "accurate" enough to roughly 12 decimal places. Revit uses double precision which technically extends to 16 decimal places but it only displays 12.

When elements in the imported/linked file are very far from the file's origin then Revit's ability (of all CAD software by the way) to accurately display and describe information begins to suffer. The Revit development team is a bit more fussy about this than how other software confronts us with this concern. One visual clue that this is affecting your project is snap icons fail to appear directly on the element it is related to.

Using Auto-Center to Center is safer from the developer's mindset, protecting us from BadCAD and or ourselves.

Now we've been bringing this up for years, asking for Revit to remember what we've used before and/or letting us set which option we prefer. The good news, from my perspective, a recent conversation with someone at Autodesk has made me optimistic that we will get our way sooner than later.


Alfredo Medina said...

I remember, in one of my classes, saying that there were 2 good options for inserting files: origin to origin, first, and then shared coordinates. I explained that any new entity in the Revit model might change its relative center, and any new entity in the link could also change its relative center, so, in conclusion, 'center to center' was a bad choice, only fine to use as a temporary placement. Then one of the students asked: "Alfredo, if that is the worst option of the three, why is it the default?" Err... good question.

Derek Renn said...

Would you say that this is more particularly true to dwg links than other Revit links?

As a consultant, we tend to link the arch rvt file origin to origin and then acquire shared coordinates from the arch model. from there we usually then link the remaining consultant rvt files with the shared coordinates option. (hoping they all are using shared coordinates too.)

Do you have any comments on this method as a consultant?

Steve said...

The post isn't advocating using Auto - Center to Center. It's just explaining why Revit is biased toward Auto - Center to Center whenever we link a file.

Specifically yes, using Auto - Center to Center would be used on DWG (CAD files). I would be VERY unlikely to use it for a Revit model.

I've written other posts about this suject but to paraphrase... consultants should link other files using Auto - Origin to Origin when they first receive another consultants file.

Once Shared Coordinates are establish by whoever is leading that task on the team, then the rest of the team can use Acquire Coordinates to "pull" the shared coordinates into their models.