Hi and welcome to my channel! I'm Lejla, a
recovering architect and a BIM and Revit specialist working at Autodesk. In my today's
video I want to tackle a very special topic I've been avoiding for a while... and no it's
not stairs :-) it's coordinates! so why is this whole topic so complicated? I think the fact that
there are many different ways to set up the Revit project and then many different ways to export
a geolocated Revit file to IFC, combined with a lot of misunderstandings how the coordinate
should behave in Revit and then in IFC creates a mess which we will try to clean up now! So let's
start with the basics: when you start a new Revit project, you can switch on the three Revit origins
in the Visibility Graphics dialogue under Site: here we can find the internal, the project base
point and the survey point. In a new project these will typically be on top of each other but you
can move the project base and the survey point depending on the project requirements. The one
point you cannot move is the Revit internal and this point was also invisible before Revit
2020, which created a lot of confusion because it really defines the magic area where all the
geometry needs to sit in and that's the 10 miles or 16 km circle. You can't move it, so please keep it
in mind. It often happens that if you load CAD files which have geometry outside of this area,
you will notice some weird behavior, like lines jumping around the screen and snapping which
seems to be a bit off and this is the alarm sign when you need to stop and clean up
your file before you do anything else! So let's set up a small project file and see how we can
geolocate our Revit file correctly. I'll first link a DWG with my site to set the context. I'll use
the Center to Center placing and then move the DWG to where I want to have it. Ideally you will
align it so that the Project base point already sits where you need it to be but you can also
move the points later on. You can also now rotate the project North (or also do it later). Once
finished I would always recommend to pin the DWG and then acquire the coordinates from it. This is
my favorite way of geolocating Revit projects because if your DWG is geolocated correctly it will also
pull the information about the GIS coordinate system like the name and the EPSG code which can
later than be exported to IFC, for example. Once you have acquired the coordinates you can still adjust
your project base point and and move it to where you need it. This is typically a building corner,
a grid intersection or something like that. One thing you should NOT do is moving the DWG or the
clipped survey point anymore, because this will change your shared cordinate system and this is
probably not what you want to do. It is actually like moving the Earth under your building and you'll need to unclip the survey point and then you can relocate it to where you need it and
this is typically somewhere on your site. Notice that the project base point and the survey point
are now reporting the shared coordinates or the GIS coordinates which means they know where
they sit on Earth. Obviously the origin of the GIS system is very far away. In the case of the UTM 32N
we typically use in Germany it's somewhere around this area, so I remind you of this when we talk
about the IFC Export options later on! Of course, if you don't have a geolocated DWG, there are other
options to set up your shared coordinate systems and I would like to mention two most used
ones: the first one is specifying the coordinates on a point and depending on whether your survey
point is clipped or not, it will either move if clipped or remain where it is, and it actually
makes no difference for the coordinate system, just for your your Revit representation of the
survey point. If you work with GIS coordinates I think it really makes no sense to clip it
and let it be moved to the origin of the GIS system because Revit knows where the origin
of the shared system is and your survey point is meant to be somewhere on your site. Another way I
often see in projects is entering the coordinates directly into the project base point and this
will basically give the project base point the information where it lives on Earth and your
survey point will remain on the origin of the coordinate system, but could again be unclipped
and moved to where you need it, for example again somewhere on your site. Now there is a lot more to
be said about shared coordinates in Revit as they are not only used for the GIS coordinate systems
but also between files to coordinate the local coordinate systems on big Revit projects. I won't go into the details here but I will link you a couple of great AU sessions below in
the video description which you can watch if you want to dig a little bit deeper into this topic.
Now there is also a tool called shared reference point for another way of coordinate exchange
between Civil 3D and Revit which I personally don't prefer. I think you might like it if you are
more on the Civil side than on the Revit side and I'll also link the exact instructions on how to
use it below if you want to check it out but basically it will deliver the same results as the
other methods. Now let's go back to the project we set up before and create some geometry which
we can export to IFC. I'll just create four walls and I'll also add markers to our Origins so that we can
analyze the exported IFCs a bit better. Now let's head over to the IFC export options and see which results
they'll deliver us. Let's first start with internal. Selecting internal means that all the geometry
in your IFC will be referenced to the location of this origin so in our case when we insert this
IFC in another software this will be the base point which needs to be known by the recipient.
Notice that despite using the Revit origin we can see the reference to the GIS system and the
exact coordinates of the Revit internal in GIS. This works only in IFC 4 and is not possible in
IFC 2x3 so I would really recommend you if you are working with GIS coordinates go for IFC4. I'll
repeat the same for all the other options. As you can see here the GIS coordinates will always
change to reflect the location of the origin selected in the world. One thing to be noted when
you export with a shared coordinate setting however is that the GIS coordinate shown here will be
set to zero which means that you are exporting the project in reference to the origin of the geo-
coordinates which I may remind you is quite far away - somewhere around South Africa and this
is also why you will get a warning from Revit and this IFC might indeed cause issues depending on
where you are using it and we'll see that a little bit later when we test and compare the exported
files. Now I'll switch to the open IFC viewer and start linking our files to see the difference.
As an additional reference I have created a small marker using a new Revit project with no
coordinates set to make sure that this marks the origin of the IFC viewer itself because
it's usually not visible and I just want to see it for testing purposes. Now let's go ahead and
load the exported IFCs one by one. As you can see the Revit internal will be mapped to the origin of
the IFC viewer which makes sense because the IFC has been exported referenced to the Revit internal.
If we load the internal with True North we'll basically get the same result as in Revit
when switching between the project North and True North. It makes sense, right? if we now load
the IFC exported with the project base point this point will again be mapped to the origin
of our IFC viewer and again rotated to True North will consider this rotation. The IFC file exported
with the survey point as reference will again map the survey point to the origin of the IFC viewer - so
actually it's pretty straightforward. Now let's see what happens with the IFC exported using shared
coordinates. At first I'm not really able to see it and if I isolate it and zoom to it, you can
see that the geometry is very distorted, simply due to the enormous distance to the origin. We
have very small geometry which sits somewhere in Germany and the origin it's referring to is
somewhere on the African Coast. So now let me clarify one thing: if I only open this one file
most of the IC viewers will actually move their own origin to this point to avoid the
geometry distortion and display everything seemingly correctly. This will work fine as long
as you load only geo-referenced files and avoid having any geometry hundreds of kilometers
away - so you can see this is not really just a Revit issue, this is happening in almost every
software simply due to the rounding that happens with these high numbers. Now what do we learn from
this? In building projects it only makes sense to have a local coordinate system and a local base
point that you refer your walls, doors and so on to. Your door doesn't need to be geolocated -
what you want to geolocate is the project so that it knows where it sits on the world and
this happens using the shared coordinates in Revit. When exporting to IFC you should stick to
IFC 4 as mentioned select a local base point, so it means Revit internal, project base point or survey
point and the geo-reference will be exported automatically in the background. Would you like
us to dig a little bit deeper into where this geolocation is actually stored in the IFC file
and how you can see it? If yes please leave me a comment and otherwise thanks for watching, leave
a like, subscribe and see you in the next video! :-)
