Visibility Graphics Issues and DWG Imports in Families

I worked through an issue this morning with a fellow RevitForum member. He was trying to determine why desks in the architect's model would not show up in one of his views, using Revit MEP. It turns out that one of the earlier replies in the thread offered part of the solution.

The desk family involved wasn't made of native Revit elements. It was only imported DWG elements. In the view that wouldn't show the desk the view's Visibility/Graphics settings were being controlled by a view template and it had the Imported Categories setting for Imports in Families un-checked. Just one or many things we need to track down when Thing's Go Missing.

Visibility Graphics Dialog and Using Current View Only

Revit 2014 introduces an enhancement regarding importing CAD data (I believe undocumented). During an Import of CAD, in the past when we used the option "Current View Only" Revit showed a reference to that link in the Visibility Graphics dialog (V/G) regardless of the view we were working in.

With Revit 2014 it now filters out the link in views that it was not imported into. Naturally if you use Copy to Clipboard and Paste Aligned to put a copy in another view Revit will start to include the link in the V/G dialog again. This is what you should see if you use Current View Only for the import.

Can't Select DWG

With Revit 2014 came new selection filtering for linked files and pinned elements.

If you find yourself scratching your head when you can't select a DWG file you just imported...remember that Revit will often pin the DWG. If you've turned off both selection options that'll make selecting the DWG doubly difficult! Been there done that!

DWG Files and Funky Snapping

Importing survey files has always been problematic with Revit. Two things are fundamental issues: large file extents and distance from origin.

Geometry that is far apart will annoy Revit, geometry more than 20 miles in extents is the current "line in the sand". Just how precise this 20 mile consideration is a little hard to pin down. There must be some specific logic or algorithm the application uses but I've tried numerous times without success to arrive at something consistently true.

For example I've tried to draw squares and cubes, even circles and spheres to test the extremes and predict the trigger of the error messages I've written about before. As soon as I think I have something I can predict I try it again and get a slightly different result. My general rule of thumb is to try hard to make sure that I don't have extents that exceed a sphere that is 20 miles in diameter.

The other issue is when the data in the CAD file is small enough in extents but really far away from the file's origin, according to the WCS which is all Revit really pays any attention to. I can have a relatively small project site survey but far from origin and end up with Revit using Auto - Center to Center to place it. That's not really a problem though. We can just tell Revit how to resolve that with the Specify Coordinates at Point tool.

Now as for the title of this post, Revit hollers when our file is "too big". The warning tells us that this situation may affect the graphic depiction of information on screen.

This manifests itself in snap icons that appear to miss the element we are attempting to reference in the CAD file. It also shows up when you use the Pick tool to place lines and the sensitivity of the tool seems offset somewhat from where we see the line.

With Revit 2013 they've added an option in the Import dialog that says "Correct lines that are slightly off axis". This is a bit of spin unfortunately because this addition means it acknowledges that Revit has been altering them before, all along. Part of the solution to the funky snapping is resolved with 2013, don't check this option.

With Revit 2012 we can still avoid it but we have to import the DWG files a little differently. The trick is to let Revit place them using Auto - Center to Center and then move files, however many you need to use, into place manually. If we try to use the trick to Specify Coordinates using one file first and then import the rest using "Auto - by Shared Coordinates" it will trigger something internally that in turn triggers the snapping issue. That trick generates a message that these files aren't sharing coordinates but the end result is that they land in the correct location because shared coordinates are matching their own understanding of the WCS.

Here's a summary of steps, sort of...

Examine your survey file and make sure it isn't too large.

If it is you need to reduce it so just the really relevant part of the site is what you import. I realize that there may be situations that challenge this assumption but if you create two files from one that provides two that are small enough to avoid the error message about extents then you can still bring them in, position them manually and then specific coordinates.

Once you've resolved the survey file checking, pick a spot in each file that can be used as a common reference benchmark. You'll need it to move them into position in Revit. Write down what the coordinates are for this benchmark.

Now you can import the files into Revit. Use the Auto - Center to Center option. In Revit 2013 don't check the "Correct lines" option. You don't have this option in 2012 but this process will still work.

Move the files into position keeping them all near the Revit project file origin. Now you can use the Specify Coordinates at Point (SCaP) tool to match up Revit with your benchmark in the cad file. Unclip the Survey Point and move it to the benchmark location. Fire up the SCaP tool and enter the matching coordinate values.

Revit now understands your real world situation. You should find that snapping to the imported file elements is not showing the graphical glitch.

Important, there is one more thing to avoid, don't create a master survey file that uses attached Xref's to combine several files together into a single file that gets imported into Revit. Doing this will trigger the snapping issue again. It does it in 2012 and 2013 regardless. I believe that the Xref's mark the origin somehow in the master file which creates an unavoidable file extents problem which brings the snapping issue back to life.

Easy?? Wish it were easier!

Extents Greater than 20 Miles

This message appears when you import a DWG file that has geometry that makes the total extents of the file larger than 20 (33 km)miles horizontally or vertically.

That message is different from this message.

The second message occurs when all the geometry in the file is farther away from the origin than Revit wants it to be, but the extent of geometry is not large enough to trigger the first warning. What that magical distance or number is, who knows. I've spent quite a bit of time trying to pin that down. The closest I've come is that when I have some geometry that is between 43,500 and 50,000 feet away from the origin of the DWG file Revit will complain. The problem with pinning it down is that as soon as I think I've got it, I change it a little and then Revit doesn't complain about importing the file. Suffice it to say that if all the geometry is pretty far away from the origin, there is a pretty good chance that you'll see that message. It isn't as far away as the first error message though (20 miles), it's more like 8ish miles.

If a file is too large to import when you've selected the correct units you can technically circumvent it by importing with different units. For example if Inches are too big, try Feet. The file will like import. Then you can reset the Units of the file and reset the scale value to 1. The file will be the correct size again. It won't prevent the graphical issues that really large DWG import can cause though. Your mileage may vary.

Another technique that has worked is to link the big file into another file as an Attached overlay. Then import the file that hosts the big one. Revit doesn't look at the Xref and doesn't complain.

In Search of a Side Door Managing Links

I wrote about the Manage Links dialog yesterday. Something else has been bugging me about it so here's another post. I'd love a side door to Import a file from the Manage Links dialog!!! It would be nice to be able to click Import File when I've realized that I need to do that instead of closing the dialog and then clicking the front door buttons for the task. Each tab could have its own side door for the appropriate file type. Crazy?

There are other precedents like the Materials browse button in the Edit Assembly dialog for walls, floors, roofs, ceilings. Another precedent, the browse button for accessing Assembly Code data?

See, not so crazy me thinks!!

Importing DWG and Exporting to DWG

Here's a few things that have come up lately regarding importing dwg data:

• Revit imports from Model Space unless there is nothing in Model Space. It then asks if you'd like to import the stuff it finds in paper space.
• Revit only recognizes the World Coordinate System (WCS)
• Revit doesn't "see" AutoCAD points, doesn't snap to them, you'll see them but can't "use" them.
• Revit doesn't "see" or even show AutoCAD Xline or Ray elements.
• Save details as single cad files not composite "sheets" of details. Single cad files can be added to individual drafting views and added to sheets allowing Revit to keep track of the sheet and detail numbers for us.
• Perfect world in Revit = no dwg files imported or linked, don't rely on them forever, work toward native Revit details and detail components.

For Exporting to DWG Revit 2012 offers the ability to define Layer Modifiers so that we can tell Revit to generate better layers for things like supply air ducts versus return air ducts.

They've also added a short list of predefined standards to pull from (technically based on the previously provided layer standard files, just presented more obviously now):

Revit and FOUS

I wrote a post back on February 1st, 2010 about the Two-Mile-Limit imposed on importing CAD files. I referred to these files as FOUS or Files of Unusual Size paying homage to the movie, "The Princess Bride". It has been mentioned quite a bit already but I wanted to update my own blog to reflect the latest development with the release of 2011.

The limit is now 20 miles, though you can still import the file. A warning is generated but the file will still be permitted, unlike before. You can read the blog post at The Revit Clinic called, "Revit 2011 2 Mile Limit Now 20 Mile Limit".

Revit and the 2 Mile Limit

I’ve read a few posts on this subject in the last few months, a couple more recently offering a way to get around the issue. I echoed a post at the Revit Clinic blog a few months ago too. Paying homage to “The Princess Bride” movie I dubbed the files affected by this issue “Files of Unusual Size” or FOUS, like the “Rodents of Unusual Size”, ROUS.

Revit examines the cad file you want to import and determines how “big” the data is. If it finds that all the data in the file results in data greater than two miles across, either horizontally or vertically it will generate the error message. It is not just that survey data is a great distance from the origin in the file. The survey itself might be fine but there is some geometry lurking a great distance from the important stuff that creates the condition that Revit is hoping to avoid.

You can test this out yourself. Create a little survey of lines and then park a line more than two miles away from those lines. It could be as simple as two lines very far apart. Import the file and Revit complains.

There are a few ways to resolve this. You can fix the file or just fool Revit into accepting the large data despite its best effort to do otherwise. The correct way should be the solution that is the least work and hopefully doesn’t put you at risk for altering the civil file in a way that leaves room for error.

To fix the file you can refer to the earlier post here or to the one at The Revit Clinic. If you are interested in fooling Revit and doing “nothing” to the file then consider this post.

Another solution that I’ve used several times is to create a new empty cad file (container file) and then create a new external reference with the FOUS in this new container file. Use the same 0,0,0 world coordinate location and make sure the external reference is attached. Now import this container file with its attached external reference, no warning message, the size of the FOUS is “hidden” by the container. Happy Imports!

Using Acad Details - An Oldy but Goody

I posted this in June 2004 at AUGI just after Zoogdesign merged with AUGI. Still true today with a couple of changes to Revit since, I wrote:

I was preparing a short discussion for our local Revit user group meeting, South Coast Revit User Group (SCRUG) to cover detailing with Revit. While not an expert at detailing as an architectural person by any means I have spent a fair amount of time working with acad details and microstation too...the following applies to AutoCAD detail files specifically but most will apply to Microstation as well.

This list was also assembled assuming that "you" are not abandoning the acad files in favor of Revit only based details. These tips will help you keep the details portable and useable in either application.

First, stay focused on your goals and choose common ground that helps you achieve them. Avoid statements that start with; "I can't..." We can't..." "I won't...."

Font and Dimension Tips:
DON'T use a width factor other than (1) in AutoCAD text styles (Revit now supports width factors in text and dimension styles but may not import them initially)
DON'T use custom symbols that aren't also present in the TTF font
DON'T use a custom leader routine and/or custom arrows/terminators

DO use a TTF font in AutoCAD OR
DO use Revit's shxfontmap.txt to map shx fonts to a TTF font in Revit)
DO use the dimension leader object in AutoCAD
DO use a standard arrow or dimension terminator
DO make sure that blocks with attributes follow these rules too

Project Mgmt and General:
DO put details in a project specific location and don't move them
DO Import and link details and check the "current view" option
DO consider a separate detail project if you are dealing with a large multi-building project
DO manage them in "one" place, for consistency (AutoCAD since that's what were talking about here)
DO use a detail specific layer structure to manage lineweights more easily if required
DO make sure your details are located near 0,0 (origin)
DO use custom programming routines to automate changes these tips require
DO make sure drafting views use the same scale as the imported detail
Do use hatches that are not too dense or too large (defining "too" varies unfortunately)
Do use hatches that are properly bounded and don't use line segments that are too short for Revit (<1/32")

DON'T move the details once linked
DON'T explode details (change them in Acad, if you want to keep them useable for both)

If you must explode (don't), do so in a separate project to isolate all the extra objects styles, line patterns and styles and fill patterns that will proliferate in the project after doing so. If you have many "line has inaccurate direction..." or "line is too short..." errors. Embed the geometry of the detail in a detail component family first. Then use that in your project, the errors will be trapped in the family and not burden your Review Warnings process, and finish detailing with Revit text, dimensions etc.

If you follow these "rules" you will find that you can, nearly always, import a detail "as is" and minimize rework on libraries that will likely remain available for both applications. (stay dwg that is)

Remember the goal probably ought to be pure Revit details eventually so I prefer to think of this as a bridging activity instead of a long term solution.

If you compare this post with the AUGI post I've added a little bit here...

DWG Import - Lines Nearly Vertical/Horizontal are Changed

Revit alters the lines in a imported cad file if they are very nearly horizontal or vertical. It has done this for quite some time. It isn't clear if it isn't a problem very often or if it isn't noticed very often. I'm reminded of this issue by a recent post at AUGI naturally.

In this instance a member wrote that a property line (in a cad import) whose bearing is 89 degrees 57 minutes and 56 seconds is altered by Revit to simply 90 degrees even. The cad file isn't "changed" but what we see of it in Revit is.

If you use Revit's Property Line tool and opt for the Table of Distances and Bearings method you'll find you can create a property boundary that is faithful to the documented bearing data.


And the dialog itself with the resulting property line.


Aah...Trust...a database or cad file is only as reliable as we believe we can trust it to be. Once upon a time people trusted that the earth was flat. That proved to be false, I think. I haven't been in space myself so I have to trust that the astronauts and scientists who say they have been are telling me the truth. Now I know that the moon is round but I don't know that it is in fact a globe because I've never seen the "back" of it. I've never seen it spinning. My life experience and acquired knowledge tells me it is a globe but assumption and belief doesn't prove it. Anyone who enjoys Robert Heinlein's books would recognize that last little bit.

Importing cad files and "seeing" nothing to cause us to doubt the accuracy of the import permits us to work with the belief that everything is fine, trustworthy. But when we discover an inaccuracy regardless how meaningful or meaningless the issue really is it places doubt in our minds. This doubt is usually worse than the actual problem we've found.

As we transition from 2D methods to 3D methods and embrace the promise of Building Information Modeling (BIM) we need to be able to trust the data. This is much bigger than just software. It has to do with each person that comes into contact with the data, the model. Our contact must be done with this issue of trust in mind so that we don't invite doubt. When doubt exists our work must stand up under close scrutiny.

Image/DWG Import Issue

My friend David Baldacchino recently shared this with me and I can confirm the problem. If you link a dwg file that also contains an image file into your Revit project, Revit will crash when you save the file. You can link it in, but Revit will crash when you save. Ouch! This happens whether you save the dwg file in either 2004 or 2007 format. Tread lightly if you need this combination...good luck! If anyone has encountered this and found a way to defeat this feel free to share in a comment. Be certain to submit the issue to Revit support at Autodesk!