hello all,
this has been bugging me for years:
Why are Topography points based on the project base point and not survey point??
I mean isn't this what the survey point is for??
Example:
My project base point (1st level) is set at 250'
I want to create my topography from the survey and points I place are also based on the project base point. WHY? Surveys are ALWAYS based on sea level 0.0. So I always end up having to 'move down' the finished topo in elevation or section to set it on the right height (250' in that case).
And if I want add a point later, I have to deduct the 250' from the actual number to place on the right height.
Anything I am missing? Why cannot we set the topography to be based on survey point? this is crazy making to me....
Gelöst! Gehe zur Lösung
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It's my own conjecture, first...the toposurface feature predates the existence of shared coordinates in Revit.
Since it is older, I believe it boils down to what they knew to be true when a toposurface is created. In the beginning there was only the project coordinate system, everything was derived relative to that.
With the addition of Shared Coordinates, they didn't redesign the toposurface tool base relationship. I imagine that's because to some degree they can't guarantee that a user will have established a site elevation relationship.
As you can see in the other thread, some of us get around it by using a separate site model and others create the surface and move it down so the correct site elevation is at the ground floor level of the project. Revit can't assume which level is the correct one to be at ground level, even if one of them happens to be at zero elevation. I've seen projects where ground floor is at X above zero and a level at zero was used for footings or somesuch. As such, the toposurface tool is referencing the easiest reliable thing it can, as it did in the beginning.
That written, it would be nice if we could choose between Project and Survey coordinate systems to define the basis for its points. Another item to toss on wish list mountain...among the thousands... They'd have to remember to change the Contour Label tool to work with it too.
Steve Stafford
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@pmartin, If it’s really bugging you and you’re not using shared coordinates; you could always build your project from sea level – starting with a very deep earthen foundation – and then place the Survey Point and building levels on top of it. ![]()
For me though: I build from the ground up and anything placed below the pad elevation is relative to my building level – not to sea level. That includes Toposurface points.
I model the site in Revit (usually from the Civil Engineer’s CAD base for the Rough Grading Plans) in order to calculate the finish grade elevations that need be shown on Plot Plans. “True” point elevations don’t concern me because I’m usually sloping earth away from and around the house to meet drainage, driveway and other slope requirements. Having the pad points at 0.0 makes the math a lot easier. Still, my Spot Elevations accurately report the “true” elevations on Plot Plans because they are set relative to the Survey Point or the “Sea Level” Level.
So, I have no problem with moving the Toposurface down once it’s created. If I have to add “true” points to it later on, and I don’t want to bother doing the math; I simply unpin and move the Topo up to its origin point, edit the surface and I then move it back down and re-pin. It’s no biggie to me.
TIP 1: If your Topo is dependent on a duplicate for cut and fill computations, I suggest you move both at the same time to avoid breaking that association.
TIP 2: Have a Level at the base of your Topo. When the Topo and its Level are at the correct elevation for your project; pull a dimension between the Topo’s Level and the Project Base Point Level (e.g. the Topo’s origination level), and then lock that dimension. This Level will serve as a “Relative Base” for Spot Elevations, should your Survey Point be needed elsewhere in the project.
Hello all,
Thank you for your feedback and the solutions.
I will basically continue doing what I always did, which I feel like is a 'work-around' (as described in the linked tread as the solution):
Separate files won't work for me any better (and I have tried that in the past as well), as I have to modify the topography on site to match the building outline and new site design. Having them separate is even more inconvenient.
Also I find building pads useless, as they can only be level and flat. Almost all my projects have underground parking and it rarely has a flat base.
They also don't give you new points to modify the topography around the building as well as they continue to refer to points underneath the pad.
I found the best/cleanest work-around solution is to hard cut out the building outline from the topo. Gives you the best control and cleanest plans/sections to work from.
(And don't get me into the fact that you cannot have topography (soil ABOVE a floor without having a mess in sections, like and underground parking extending into setbacks...which happens in 99% of my projects).)
It would just be nice to have the option to base the topography on the survey point as it seems much more logical to me. (Wouldn't this be one of the major reasons to have a survey point...). One can dream....
Again, thank you all and happy modeling.
Just for the record...a building pad can slope (via Slope Arrow). That doesn't necessarily mean sloping them is easy, fun or effective for what you want to do.
I prefer to use them to create excavation and make them thin, imagine a vapor barrier. Then I place floor slabs over that.
Steve Stafford
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This is hands down the best explanation of anything related to survey point, project base point, and topography I have encountered on the internet. Read through these 13 tips and you will have a better understanding of how all this stuff works.
https://revitpure.com/blog/13-tips-to-understand-revit-base-points-and-coordinate-system
FWIW, here's one of my favorites:
http://paulaubin.com/_downloads/2011_AU/Papers/AB3733_Aubin_SharedCoord.pdf
That blog post reiterates things I've been writing on my blog for 14 years. None of this is any mystery to me. Perhaps you were replying to someone else.
Steve Stafford
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You're still the king in my book, @SteveKStafford -- and not just on this Topic. Your Revit OpEd Blog has schooled me on many, many Revit topics over the years. Thanks.
Hah, flatterer... Sadly it just means I've been around so long, the old dog.
Steve Stafford
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What do you mean with "hard cut out the building outline from the topo" ? without using a building pad? do you place points at the bottom of the concrete floors?
The Survey point seems to be useless. We have have most success with using the toposurface in other files and publishing the co-ordinates back to the model. It makes sense to do it in one file but I think the limitations in the toposurface are just too hard.
When are the tech heads that write the code start to ask how we work in the real worls. You should be able to build a model in a site so much easier.
thanks Craig. Yes, I agree. It's very confusing and difficult to work with although I think I may have a better understanding of it but that's after several hours, if not days, of trying to work through it.
Yes - like you it took us a few days of trial and error. It's not really good enough for Autodesk in my opinion
The Survey Coordinate System is integral to positioning a model relative to a survey/civil DWG. The Survey Point itself is just a tangible icon, piece of the system.
That the toposurface element does not reference it is a separate issue. There is no guarantee the SCS will be sorted out/defined prior to a user creating it (topo) so the Project Coordinate System is used as its "foundation". I think it's a practical and reasonable decision from the developer's standpoint. If not then people would inevitably complain that they can't create a toposurface because they aren't ready to set the Survey Coordinate System yet.
I think it would be useful to be able to tell a toposurface which coordinate system it should reference. Maybe they'll do that in the future.
Steve Stafford
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@SteveKStafford wrote:
I think it would be useful to be able to tell a toposurface which coordinate system it should reference. Maybe they'll do that in the future.
You got me scratching my head about this statement, @SteveKStafford. We can already “tell” a Toposurface which coordinate system it should reference. What could improve in the future?
If you create a toposurface by placing points they only reference the Project Coordinate System.
Steve Stafford
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@SteveKStafford wrote:
If you create a toposurface by placing points they only reference the Project Coordinate System.
Project Coordinate System as in Internal Coordinate System, @SteveKStafford? Toposurface Points are based on the Internal Origin. This origin of the Internal Coordinate System provides the basis for the Survey and Project Coordinate Systems. You taught me that. That was an “aha moment” for me, and the most enlightening discussion I ever had on this forum, thanks to you.
Yup...I'm oversimplifying. The language Autodesk has been using has evolved over time. Most of the time my use of the terms Project Coordinate System and PBP are no different than the internal origin/coordinate system. It only manifests as different or special when it is un-clipped and relocated.
As for improved... I'd like to be able to specify actual contour elevations when I create a toposurface inside a building model even though the building is at "zero" elevation versus working in a separate site model where the values I provide are the actual elevation. In that context I'd define what the ground floor elevation should be using Relocate Project "up" to that elevation. When I create a toposurface I'd change a property that offers Survey Point or Project Base Point. Using Survey Point would allow me to enter a value like 465.5' instead of having to figure out what the project elevation offset would reduce that to.
Steve Stafford
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