Project North vs True North

[aperez.126820]

Can anyone explain how true north and project north should be used?
Everything I've seen in Revit Help seems counter-intuitive, and it is unclear why I can not change and/or rotate project north.
How I think it should work is:
1. Views that are intended to be placed on sheets (orthogonal to the sheets) would be set to "Project North" in the view properties.
2. I would expect PN to then be oriented as set in the Tools/Project Pos./Rot

When I go to Revit Help, it explains that True North should be set for "sheet views".
The opposite seems to be what I would expect. (i.e. PN on sheets)

How we currently work around this issue is:
1. Import a cad survey file that contains a TN arrow.
2. Rotate the survery file that includes TN arrow.
3. Rotate TN via Tools/Project Pos./Rot. based on the angle used to rotate the survey.

This process works but requires the rotation of the cad file.

Can someone explain how this whole process and/workflow is expected to be handled?

Thanks
ap

[Steve_Stafford]

Revit assumes you are going to place/model your building on paper to make it easy to document. Be selfish, make it fit on your page conveniently.

All views (plan/rcp) are assigned a project north orientation by default.

When you determine the true north orientation of your building you can rotate it to define how the bldg will sit on site. Then the few views that need to show true north orientation can have their orientation parameter assigned to True North. This way you can show either True North or Plan North (Project North) easily. It is structured this way because we may not know exactly how how building will sit on site early enough to do that task first.

I prefer to create a separate model for site so that I can link my building model into the site later to manage its location and elevation more easily via Shared Coordinates. Not everybody agrees with me but I like it. I wrote an article on my blog (http://revitoped.blogspot.com/2006/06/true-elevation-and-position.html) about it.

Good luck!

[Dimitri Harvalias]

All views (plan/rcp) are assigned a project north orientation by default.

Just to clarify, Revit's default always assigns up in the view window as Project North.

[LRaiz]

aperez,

Your assumptions are correct.
1. Views that are oriented according to natural orientation of the building should be set to "Project North" in view properties. You refer to such views as "indented to be placed orthogonal to sheets".
2. Tools/Project Position/Rotate is one of the ways to change Project North relative to True North. However it may or may not behave intuitively depending on your use (or misuse) of shared coordinates.

Here is one possibility of overall intended work flow that hopefully feels natural

Link in (not import) a dwg file that is oriented according to survey coordinates.
Move (not just in plan but in elevations as well) and rotate linked file to position site relative to your building.
Acquire shared coordinates from dwg file. This is an important step that should not be missed. It basically tells Revit that surveyor file internal coordinates should be used as shared coordinates and thus define True North. Besides, using acquire instead of publish avoids making changes to dwg file. Once shared coordinates are established Tools/Project Position commands will move/rotate your project relative to site.
Change properties of plans that should be oriented according to surveyor coordinates to True North.
Make sure to select an option to use shared coordinates when outputting dwgs that are intended to be in surveyor coordinates.


HTH

[chris.needham]

aperez,

Your assumptions are correct.
1. Views that are oriented according to natural orientation of the building should be set to "Project North" in view properties. You refer to such views as "indented to be placed orthogonal to sheets".
2. Tools/Project Position/Rotate is one of the ways to change Project North relative to True North. However it may or may not behave intuitively depending on your use (or misuse) of shared coordinates.

Here is one possibility of overall intended work flow that hopefully feels natural

Link in (not import) a dwg file that is oriented according to survey coordinates.
Move (not just in plan but in elevations as well) and rotate linked file to position site relative to your building.
Acquire shared coordinates from dwg file. This is an important step that should not be missed. It basically tells Revit that surveyor file internal coordinates should be used as shared coordinates and thus define True North. Besides, using acquire instead of publish avoids making changes to dwg file. Once shared coordinates are established Tools/Project Position commands will move/rotate your project relative to site.
Change properties of plans that should be oriented according to surveyor coordinates to True North.
Make sure to select an option to use shared coordinates when outputting dwgs that are intended to be in surveyor coordinates.


HTH

I wish I had tried the acquire shared coordinates sooner, as the trial and error method I've been using is frustrating.

What happens if I want to rotate/move the linked file after acquiring shared coordinates? I've just tried it, then tried to acquire shared coordinates again, but revit informs me that "the shared coordinate system of the project you selected is already synchronised with the current project." How can I get the new coordinates?
I tried linking in the file again, and acquire coordinates of the newly linked file, and get the same error.
Any tips for this problem?

[LRaiz]

After acquiring sharing coordinates for the first time you don't need to do it again. As I stated in item 4 of my earlier post you may use Project Position commands to change position of your building relative to its linked file surroundings. Once shared coordinates are acquired moving/rotating your project will move it relative to shared coordinates but will keep links pinned to their surveyor coordinate placement.

If on the other hand you attempt to move/rotate linked file placed via shared coordinates then Revit warns you. You may ignore this warning and then Revit assumes that linked file is no longer positioned by shared coordinates but it 'thinks' that shared coordinates still make sense for the active project. If later on you attempt to reacquire shared coordinates Revit will warn you again. I know that this behavior may be confusing but it is actually reasonable in some situations with multiple links which all use shared coordinates. In order to avoid the confusion just remember to use Project Position commands if your intent is to move building on site after shared coordinates are established. (Disclaimer - at the moment I don't have Revit installed to verify every little detail of this paragraph; I am speaking from memory)

Makes sense?

[chris.needham]

After acquiring sharing coordinates for the first time you don't need to do it again. As I stated in item 4 of my earlier post you may use Project Position commands to change position of your building relative to its linked file surroundings. Once shared coordinates are acquired moving/rotating your project will move it relative to shared coordinates but will keep links pinned to their surveyor coordinate placement.

If on the other hand you attempt to move/rotate linked file placed via shared coordinates then Revit warns you. You may ignore this warning and then Revit assumes that linked file is no longer positioned by shared coordinates but it 'thinks' that shared coordinates still make sense for the active project. If later on you attempt to reacquire shared coordinates Revit will warn you again. I know that this behavior may be confusing but it is actually reasonable in some situations with multiple links which all use shared coordinates. In order to avoid the confusion just remember to use Project Position commands if your intent is to move building on site after shared coordinates are established. (Disclaimer - at the moment I don't have Revit installed to verify every little detail of this paragraph; I am speaking from memory)

Makes sense?

Yes, I think I have it now.

Thanks very much for your help.

[Simon.Whitbread]

3.Acquire shared coordinates from dwg file. This is an important step that should not be missed. It basically tells Revit that surveyor file internal coordinates should be used as shared coordinates and thus define True North. Besides, using acquire instead of publish avoids making changes to dwg file. Once shared coordinates are established Tools/Project Position commands will move/rotate your project relative to site.
HTH

This is a great subject and I know one that has lead to many frustrations in the past especially for novice users. However, there is one thing that still causes some confusion for a few users.

In New Zealand, surveyors typically create a DWG where the origin / UCS could be 65km from the actual site. They use a common point to set out from for ALL locations. So when the site is imported, it can be difficult to find


The site DWG
your Model!
In the past I've experienced problems with Sun and shadow studies where the surveyors DWG has been created this way and haven't been able to get good results until the DWG has been changed to have a UCS that is what I consider to be within a reasonable distance from the site (ie within 1-200m).

I guess my question is:

With a survyors DWG, does it matter where the origin is, and if so, should it be reasonably close to the site boundary?

I have up till now, recommended that the site be located within a (typically) 100sq m grid with the origin - see attached.

Are there any recommendations on this procedure?

Thanks

Simon

[Dimitri Harvalias]

Simon,
Check out this post as well as doing a search of the forums for more info
http://forums.augi.com/showthread.php?t=53687&highlight=origin
This is a known issue in Revit and can be a source of frustration when dealing with surveys or other CAD data where the origin is far away from Revit's.

[Simon.Whitbread]

Thanks Dimitri,


I hope those I support take note and stress to surveyors that this is the way architects need to work.

It's been a known issue for some time and one that occasionally needs reinforcing.

[chris.needham]

Thanks Dimitri,


I hope those I support take note and stress to surveyors that this is the way architects need to work.

It's been a known issue for some time and one that occasionally needs reinforcing.

Hi Simon.

I've typically been using Autocad to move the survey data be be centred roughly on 0,0 prior to linking into Revit, rather than it being way out in space.

The info from Leonid has been helpful for me, and made the whole "rotate true north" thing a lot clearer.

[MTristram]

This is all well and good until you need to identify a true N/E for a contractor on site - how do you propose to get around that?

We currently have a project where we need to have the true northings and eastings for the project, if we move the survey data we are no longer able to obtain these coordinates.

[Dimitri Harvalias]

For on site layout you can create northings and eastings from any point on site and have Revit report them relative to that point.
As is usually done the layout point can be established using the 'real' survey bench mark (wherever it might be) and then all on site work is laid out relative to the site benchmark.