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Thread: The Moving Linked CAD file (Project North True North)

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    Lightbulb The Moving Linked CAD file (Project North True North)

    Just wondering if anyone ever had issues with linked in CAD files moving for no reason?
    This issue deals once again with Shared Coordinate Systems and True North.

    Many of our esteemed colleagues have written in depth explanations about how Shared Coordinate System works and how it relates to Revit's Project origin.

    So here are the things that we know about specifying a shared coordinate of CAD files a large distance away, and have been talked about on the forums for quite some time.

    1. Build your Revit Geometry Close to the Revit Origin. Revit doesn't like large numbers when it does it's calculations.

    2. When inserting your CAD site plan file for the first time, drop in Center to Center. Move/ Rotate the CAD files in both plan and elevation, to be oriented to the Project North.

    3. After Placement use the acquire coordinates tool from Revit Tools menu. Upon acquiring the coordinates, Revit will take the following action; revit will assume the XY (0,0,0) WCS location of the CAD fileas the shared coordinate system, wherein the Y axis is True North.

    4. We only need to do this once, because everytime you insert a new cad file, if it doesn't share coordinates with Revit, then Revit will match the WCS of the CAD file to the Shared Coordinate.


    This sounds all fine and dandy, and looks great on paper. I even did an entire discussion at a Chicago Revit User's Group on the topic.

    Now here's the onion. Per Wes McCauley's post on the topic:

    http://forums.augi.com/showthread.ph...ghlight=origin

    What I described in steps 1-4 above runs in tandem with Mr. McCauleys post, but herein lies the problem. Revit never really gets away from hating large numbers. So if you have a site survey file wherein your site scope is a large distance away from your acquired Revit Shared Coordinate system, Revit will hiccup and lose the position of the CAD file upon File open and/or Manage Links reload. This appears to be completely random. Sometimes it shifts left, sometimes up, sometimes down, sometimes diagonal. It really doesn't seem to have a rhyme or reason to its relocation. When it does this, it also loses the object style settings of your import object dialogue, such as specific CAD Layers you set to be grey. What is really upsetting is that it will behave itself for weeks on end and then all of a sudden the night of your submission deadlines, all your CAD site information flys off in Random Directions. This takes place no matter which methodology you use to save the shared coordinate system into your CAD file, or even if you rely on the default WCS placement to the Shared Coordinate

    Try correcting this everytime you issue, and you will surely want to do a triple gainer off the nearest balcony.

    For a while I sucked it up and manually fixed the CAD files everytime Revit burped, however I began to notice a trend. It appeared that upon Revit reloading the CAD file it would only shift under the following condition:

    -You have added or deleted a large chunk of CAD data, near the extents of your original drawing. When this takes place, upon Revit reloading the CAD file, Revit will decide to re-orient your CAD drawings to what suspiciously started to look like a Center to Center placement, i.e. if you added a large chunk of data to the north of your project, everything would shift down to be on the new center. If you added a large chunk of data to the Southwest of your drawing, it would relocate diagonally to the right and up. The random distance accredited to how much volume of information went beyond the original extents of your CAD file.

    So the solution......I think it works.....none of my bloody CAD files have moved yet, and as I write this a major submissions is only hours 12 hours away.

    -Draw a bounding box that is larger then the extents of your site cad file. Instruct your users to never draft cad elements outside of the provided box. This in turn will cause Revit to never see the change in the extents of the CAD file linked in, thus causing for a happy CAD file that stays where it is supposed to be. Looks good on paper, I think!

    Now for the caviat... optimize the size of your bounding box. There is a sweet spot. If your bounding Box is rediculously large, then Revit will burp and forces the link to come in on center, even if you have the shared coordinate up and running. If your bounding box is too small then you are not providing enough space to add additional content and data.

    Unfortunately, it's too early for me to say that this work around is a sure thing. I would love for fellow AUGI members to test my findings and comment.


    --Regards

    A Very Sleepy SOM Revit Guru

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    AUGI Addict aggockel50321's Avatar
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    Default Re: The Moving Linked CAD file (Project North True North)

    I've had the same issue.

    What seems to have solved it for me is once I have the cad file positioned where I want it is to go to File / Manage links, then highlight the file in the dialog, and push the "save location" radio button on the bottom left of the dialog.

    Since doing that, I haven't had one move....yet....although I'll have to try a test of adding stuff in acad near the drawing's extents, and see if I get your result...

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    Default Re: The Moving Linked CAD file (Project North True North)

    Ohhh it even does this when you use the radio button to save the location.

    This problem only happens with cad files with content a large distance away from the WCS origin. Typically when it exceeds 1.5 files from the origin point.

    --Cheers

    SOM Revit Gnome

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    Default Re: The Moving Linked CAD file (Project North True North)

    Hi,

    I have done everything you wrote in your steps.
    Unfortunately when I go to reload the cad file (site plan) it rotates into a strange position.

    Do you have any idea? This seems strange because this exact cad file is what I used to acquire coordinates for the project.

    Quote Originally Posted by mkim View Post
    Just wondering if anyone ever had issues with linked in CAD files moving for no reason?
    This issue deals once again with Shared Coordinate Systems and True North.

    Many of our esteemed colleagues have written in depth explanations about how Shared Coordinate System works and how it relates to Revit's Project origin.

    So here are the things that we know about specifying a shared coordinate of CAD files a large distance away, and have been talked about on the forums for quite some time.

    1. Build your Revit Geometry Close to the Revit Origin. Revit doesn't like large numbers when it does it's calculations.

    2. When inserting your CAD site plan file for the first time, drop in Center to Center. Move/ Rotate the CAD files in both plan and elevation, to be oriented to the Project North.

    3. After Placement use the acquire coordinates tool from Revit Tools menu. Upon acquiring the coordinates, Revit will take the following action; revit will assume the XY (0,0,0) WCS location of the CAD fileas the shared coordinate system, wherein the Y axis is True North.

    4. We only need to do this once, because everytime you insert a new cad file, if it doesn't share coordinates with Revit, then Revit will match the WCS of the CAD file to the Shared Coordinate.


    This sounds all fine and dandy, and looks great on paper. I even did an entire discussion at a Chicago Revit User's Group on the topic.

    Now here's the onion. Per Wes McCauley's post on the topic:



    What I described in steps 1-4 above runs in tandem with Mr. McCauleys post, but herein lies the problem. Revit never really gets away from hating large numbers. So if you have a site survey file wherein your site scope is a large distance away from your acquired Revit Shared Coordinate system, Revit will hiccup and lose the position of the CAD file upon File open and/or Manage Links reload. This appears to be completely random. Sometimes it shifts left, sometimes up, sometimes down, sometimes diagonal. It really doesn't seem to have a rhyme or reason to its relocation. When it does this, it also loses the object style settings of your import object dialogue, such as specific CAD Layers you set to be grey. What is really upsetting is that it will behave itself for weeks on end and then all of a sudden the night of your submission deadlines, all your CAD site information flys off in Random Directions. This takes place no matter which methodology you use to save the shared coordinate system into your CAD file, or even if you rely on the default WCS placement to the Shared Coordinate

    Try correcting this everytime you issue, and you will surely want to do a triple gainer off the nearest balcony.

    For a while I sucked it up and manually fixed the CAD files everytime Revit burped, however I began to notice a trend. It appeared that upon Revit reloading the CAD file it would only shift under the following condition:

    -You have added or deleted a large chunk of CAD data, near the extents of your original drawing. When this takes place, upon Revit reloading the CAD file, Revit will decide to re-orient your CAD drawings to what suspiciously started to look like a Center to Center placement, i.e. if you added a large chunk of data to the north of your project, everything would shift down to be on the new center. If you added a large chunk of data to the Southwest of your drawing, it would relocate diagonally to the right and up. The random distance accredited to how much volume of information went beyond the original extents of your CAD file.

    So the solution......I think it works.....none of my bloody CAD files have moved yet, and as I write this a major submissions is only hours 12 hours away.

    -Draw a bounding box that is larger then the extents of your site cad file. Instruct your users to never draft cad elements outside of the provided box. This in turn will cause Revit to never see the change in the extents of the CAD file linked in, thus causing for a happy CAD file that stays where it is supposed to be. Looks good on paper, I think!

    Now for the caviat... optimize the size of your bounding box. There is a sweet spot. If your bounding Box is rediculously large, then Revit will burp and forces the link to come in on center, even if you have the shared coordinate up and running. If your bounding box is too small then you are not providing enough space to add additional content and data.

    Unfortunately, it's too early for me to say that this work around is a sure thing. I would love for fellow AUGI members to test my findings and comment.


    --Regards

    A Very Sleepy SOM Revit Guru

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    AUGI Addict MikeJarosz's Avatar
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    Default Re: The Moving Linked CAD file (Project North True North)

    Marcus Kim wrote his post in 2007. Too bad SOM has offices in Chicago and NY. Writing from SOM-NYC, two years earlier, James Vandezande advised to use center-to-center. An old buddy of mine, you might say James "wrote the book". Too bad Marcus was 1000 miles away

    [URL="http://forums.augi.com/showthread.php?44472-Revit-and-AutoCAD-UCS&highlight=Revit+AutoCAD+UCS"]

    Years later, David Conant warned "NEVER import or link a site with large coordinate values Origin to Origin!"

    [URL="http://forums.augi.com/showthread.php?76219-Shared-Co-Ordinates"] Check out response #4 to this post.

    I have offered a possible explanation for this behavior for years now, only to have my ideas fall on deaf ears. Here we go again. Maybe someone from inside Autodesk will hear me this time. I admit the technical nature of my observations will probably not be of much interest to the average Revit user, but it could motivate someone at AD who knows, to look into this continuous source of irritation to Revit users.

    When writing a computer program, the author must choose how to represent the anticipated range of the data to be processed. In simple terms, programming languages offer numbers that are small, medium, large and extra-large. (apologies to Rem Koolhaas!) If I create a variable as an integer (i.e. small), in most systems that will limit it to 32,767. Encountering a number larger than that will create an overflow error and screw everything up. I believe this is why Revit limits the distance from the origin. Deliberately or not, they chose a number format that has a relatively low upper limit to represent the distance from the Revit origin. Any distance that exceeds the limits of that number type will fail. The two miles they often cite as the limit is about 10,500 feet, not a large number by anyone's standard, assuming units are stored as feet. Even inches are no big deal.

    I am willing to give AD the benefit of the doubt, that there is a good reason for this limitation, but why not let us in on the secret. It might stop the semi-annual complaints about this limitation. Or, you could switch the variable to double precision and be done with it!

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    Default Re: The Moving Linked CAD file (Project North True North)

    Did you try to simply specify the coordinates instead of acquiring them? I find this more reliable when i work with large CAD files.

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    Default Re: The Moving Linked CAD file (Project North True North)

    I usually "clean" the cad files before importing. Preferably also move everything inside it closer to 0,0,0 (with some arb round figure which I note down somewhere).

    The main issue usually is that even using c2c placement doesn't always work. Especially on stuff like surveys (which are the most prevalent for this). If they have things like ordinate dimensions, there's some "dot" placed on the 0,0,0 so the "centre" of the drawing actually shows nothing - it's half way between the origin and the actual drawing.

    As for the limits, I think adesk placed an artificial limit. Because even though double-precision has an upper limit which is quite huge, the precision only goes to around 16 decimal digits. So if the distance from origin is more than 16 decimals of the current units, you're going to loose accuracy by more than one unit. So if you place a wall of 10,000 mm long at some huge distance of a few parsecs from the origin - it might show as 0mm long or even 100,000,000 mm ... no way of telling which side the error will go to.

    I think adesk might have added some check to ensure that all imports are far below that, just to be on the safe side. They might have over compensated a bit. But I don't believe they used some inferior floating point type, it's highly unlikely that they'd even go to single-precision as the DWG already uses double and would thus make importing / linking inefficient since it needs conversion.

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    Default Re: The Moving Linked CAD file (Project North True North)

    Quote Originally Posted by MikeJarosz View Post
    Marcus Kim wrote his post in 2007. Too bad SOM has offices in Chicago and NY. Writing from SOM-NYC, two years earlier, James Vandezande advised to use center-to-center. An old buddy of mine, you might say James "wrote the book". Too bad Marcus was 1000 miles away

    [URL="http://forums.augi.com/showthread.php?44472-Revit-and-AutoCAD-UCS&highlight=Revit+AutoCAD+UCS"]

    Years later, David Conant warned "NEVER import or link a site with large coordinate values Origin to Origin!"

    [URL="http://forums.augi.com/showthread.php?76219-Shared-Co-Ordinates"] Check out response #4 to this post.

    I have offered a possible explanation for this behavior for years now, only to have my ideas fall on deaf ears. Here we go again. Maybe someone from inside Autodesk will hear me this time. I admit the technical nature of my observations will probably not be of much interest to the average Revit user, but it could motivate someone at AD who knows, to look into this continuous source of irritation to Revit users.

    When writing a computer program, the author must choose how to represent the anticipated range of the data to be processed. In simple terms, programming languages offer numbers that are small, medium, large and extra-large. (apologies to Rem Koolhaas!) If I create a variable as an integer (i.e. small), in most systems that will limit it to 32,767. Encountering a number larger than that will create an overflow error and screw everything up. I believe this is why Revit limits the distance from the origin. Deliberately or not, they chose a number format that has a relatively low upper limit to represent the distance from the Revit origin. Any distance that exceeds the limits of that number type will fail. The two miles they often cite as the limit is about 10,500 feet, not a large number by anyone's standard, assuming units are stored as feet. Even inches are no big deal.

    I am willing to give AD the benefit of the doubt, that there is a good reason for this limitation, but why not let us in on the secret. It might stop the semi-annual complaints about this limitation. Or, you could switch the variable to double precision and be done with it!
    You're right Mike there is a good reason, it comes down to processing efficiency: reducing the memory size allows for more operations thus better performance. Revit was designed with this in mind where the rendering performs better compared to AutoCAD. It was never intended for Revit to have 2 miles of active drawing space. This is why you sometimes see graphical glitches when manipulating a view with a DWG overlay.

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    Default Re: The Moving Linked CAD file (Project North True North)

    Quote Originally Posted by mkim View Post
    Try correcting this everytime you issue, and you will surely want to do a triple gainer off the nearest balcony.
    This issue confuses me to no end. At least 12 years of a known bug, and we've had no fix yet?

    We do a lot of work on drawings in coordinates. That is, after all, the entire point of the True North / Project North variable. In today's BIM projects, you need your collaboration and IFC export and CAD imports all to work in the same Coordinates system.

    Now, Iceland's coordinates system is (for example) 350,000,000 x 420,000,000, which means that two CAD files linked together (thanks to AutoCAD actually including the base point of the linked file into it's own file) will have an outer boundary of ~400 million units. Center to Center loading of these files into Revit will them move the files about 200 million units away from project center. Or in this example, 125 miles away.

    This is just ridiculous. And if I actually attempt to load the CAD files as Shared Coordinates, Revit won't allow me to save the Revit project because it can't save the coordinates into the CAD files. Infinite loop of annoyance.

    Then, to top if all off, once I've loaded the file in C2C, and then moved it a hundred miles to the correct place, if I got right back in and Reload the CAD file, it moves it away again and rotates it.. even though nothing's changed in the CAD file between loads. So I've made it a habit of always reloading the CAD files three times before moving them and pinning to the correct location.
    But then I always have to make sure to be in True North when I reload the files, to stop it from rotating away from me.

    I'm on the 4th floor of a 9 floor office building. That triple gainer is starting to look real good. And the balcony isn't very far away!

  10. #10
    Revit Forum Manager Steve_Stafford's Avatar
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    Default Re: The Moving Linked CAD file (Project North True North)

    My fourth blog post (in a series of four) brings up the moving CAD file issue.

    It is one of the reasons I always use a separate site model.

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