1. Locked geometry and linework.
2. Locked dimensions.
3. Equal dimensions.
4. Parametric dimensions (type and instance).
5. Automatic sketch dimensions.

The first 4 items are pretty well covered in tutorials so I’m not going to go into any great detail on these. I just wanted to touch on a couple points I haven’t seen in a tutorial yet.

Geometry and linework should always be locked to a reference plane or line and then the reference plane or line should be adjusted with labelled parameters. This will make your family more stable and predictable when flexed.

Locking an equal dimension has the effect of double constraining. Not only will the constrained object maintain its position equally but it’s length will be fixed as well.

Locking a parametric dimension will “maintain the parametric relationships between labeled dimensions“. Huh? This one really needs an example to make sense.

Figure 1.

In figure 1 above, the black dashed line is constrained by 2 labelled dimensions which are using the same parameter “test1″. The horizontal dimension constrains the length of the line while the vertical dimension controls the lines position relative to the horizontal reference plane (shown in green). If I were to move the dashed line line up or down, the default action of Revit is to change the value of the test1 parameter to the new distance between the horizontal reference plane and the dashed line and as a result the length of the dashed line would change to match this value (since it is labelled with the same parameter). However, if I lock one of the dimensions (it doesn’t matter which) all the dimension labelled with the same parameter will become locked as well. Which means if I attempt to move the dashed line up or down, Revit will will issue a constraints not satisfied error when it attempts to change the length of the line to the new value (because it is locked).

Automatic sketch dimensions (autodims) are hardly mentioned in most Revit blogs, tutorials and documentation I’ve read and are hidden in the Revit family editor by default. Surprising really because these are really the guts of how Revit constrains a family when flexed.

Important note: Temporary dimensions are not the same as automatic dimensions. Temporary dimensions appear when you select an object in Revit, autodims remain visible unless specifically turned off. In figure 2 below, the black line is not selected.

As I mentioned autodims are hidden in the Revit family editor by default. This is because every time you create a line or geometry the autodims are automatically created for it and after a while your screen can become quite unreadable. To make the autodims visible here’s what you need to do:

1. In the “Visibility/Graphic Overrides”, go to the “Annotation Categories” tab and click the check box next to “Automatic Sketch Dimensions”. It is a sub category under “Dimensions”.
2. Draw a reference plane to constrain with a labelled dimension, in figure 2 below I drew a reference plane and labelled it with the test1 parameter (type or instance doesn’t matter). At least one labelled dimension is required otherwise you can’t flex the family and therefore autodims wouldn’t be required.
3. Draw a line (symbolic or model) and you will notice that blue dimensions automatically appear on the screen. These are the autodims and they are telling you how that line will behave when the model is flexed.

Figure 2

Without the autodims showing it would be easy to think that the black line in figure 2 would not be affected in any way if the parameter test1 was changed. However that autodims show us quickly how it will be changed. On the left side, there is a horizontal autodim connected to the left vertical reference plane (shown in green) and on the right side is another autodim connected to the other vertical reference plane. These autodims act as locked dimensions, so when test1 is set to 5′-0″ the end points of the lines will be adjusted to maintain the value of the autodims. This will change the length AND angle of the black line, see figure 3 below.

Figure 3

There is a way to change the behavior of autodims. Like normal dimensions the  witness lines can be edited so that the autodims connect to other objects. This is dangerous however because even though an autodim acts like a locked dimension you can still adjust the end point of the line without getting an error. Revit just creates new autodims when the line is manually adjusted and any changes you made to the witness lines of the autodims are lost.

Autodims (being automatic) will self adjust as required in the family editor. When you manually adjust the shape or location of a geometric shape or line the autodims will adjust too. Also if you create a labelled or locked dimension the autodims will also adjust, in this case some might completely disappear if they are over constraining the family.

One last note, autodims of 0′-0″ means the end point of the line is sitting directly over something and will move with it.

Conclusion

Just a few more handy tips when creating families.

• When the work plane is based on a reference plane (not a face), the centre of a circle will autolock to 2 intersecting ref planes. This is handy for creating things like table legs and it works when copying too.
• When an instance parameter is used between two reference planes, Revit will draw arrows (when the family is used in a project) that the user can drag with a mouse to adjust the distance. No need to go to the properties palette.
• Parameters can also based on formulas (similar to formulas in spreadsheets). For example, a parameter can be set to equal the sum of two other parameters or even be set to a certain value if another parameter is greater than a another parameter. This topic is rather lengthy however and I won’t post on it unless asked too. There is information in the Revit documentation on this.

Thanks for reading, see you soon. Feel free to ask questions in the comment area below.

Lines

If reference planes are the skeleton and labelled dimensions are the muscles of the family, reference lines are the joints in the skeleton. They define which way the parts of the skeleton can bend (rotate) but they can also do more.

Start and end points

As I mentioned in last weeks post, reference lines have a start and end point, unlike reference planes. This provides additional data to Revit when you are trying to use angular dimension parameters in a family. When constraining a reference line to a reference plane as shown in the image (Fig. 1) below, the vertex point of the rotation is not the intersection of the reference line and the reference plane. It is either the start (1) or end (2) point of the reference line.

Figure 1

In this example Revit assumed that the start point (1) of the reference line was meant to keep it’s relative position to the two reference planes which means that the end point (2) will move when the “r” parameter is changed. This can be changed however by locking the end point (2) to the reference planes with locked dimensions. Then the start point (1) will change location.

While we’re on the topic, the length of a reference line can also be adjusted using parametric dimension or by locking the end points to reference planes. This is how line based families work. I’ll cover parametric dimensions more in a later post.

Associated work planes

Another major difference between reference planes and lines is the number of work places associated with them. A reference plane only defines one work plane which can be named in the properties palette. A reference plane has four work planes associated with it. See figure 2 below.

Figure 2. A selected reference line in a 3D view.

A reference line has 2 work planes that run along the length of the line and intersect one another along that line. There is also a work plane at the start and end points of the line that are perpendicular to the line. To specify which work plane you want to model or draw on start the “Set work plane” command (Select the Home->Work Plane->Set icon) and select “Pick a Plane” from the popup dialog. Then with your mouse over the reference line press the tab key to cycle through the work planes on the line. You need to be over the start or end point to select that work plane. Drawing on these work planes allows those parts to rotate with the reference line, since the work planes rotate with the line.

Conclusion

These posts will get complicated real fast and I’ll do the best to keep them simple. The best way to learn this stuff is to open Revit and try out what I’m talking about. In the next post, I’m going to go over parametric dimensions including automatic dimensions which might help explain some of those mysterious outcomes you have when flexing a model for the first time.

References

There are 2 kinds of references in Revit families: Planes and Lines.

The Difference

There is a huge difference between the two and the difference is this: to Revit Planes are infinite in length while Lines have a start and end point. So what? Well it makes a difference if your trying to create a family that has a variable angle (rotation) to part of it. Say a north arrow that also shows a project north at some variable angle off true north. If you attach your project north line-work to an infinite line and then rotate that line what point does it rotate around? Revit needs to know the centre point of the angle that is changing in order for a consistent result to happen. Since a Reference Plane is infinite in length, the centre point can be anywhere along the plane. The result is the plane will rotate but the project north arrow will appear to move away from the true north arrow but never the same way twice.

There are other differences but this is the big one.

Planes

Reference planes are the skeleton that give the family it’s form, while labelled dimensions are the muscles that move it. Everything else should be attached to the skeleton.

When you select a plane there are 3 important properties you can edit in the Properties Pallete:

• Name – this property is for making editing the family easier. When you name a reference plane, the name will appear in the pull down list when you are specifying a new work plane.
• Is reference – this property will affect how the family is dimensioned IN A PROJECT. If this is set to “Not a Reference”, the plane will not be able to be dimensioned to. It will be completely invisible when loaded into a project. “Strong” and “Weak” references indicate which plane will be shown by Revit first. To dimension to a weak reference you will have to tab to it. Strong references will always be highlighted first. Any other value here (and you don’t need to use just the ones given) are for maintaining dimensions when switching to a different family. For example, if you have all your windows dimensioned to the “Center (Left/Right)” plane and you change from one window type to another, Revit will re-attach the dimension. If there is no “Center (Left/Right)” plane in the new window type the dimension will be deleted.
• Defines Origin – you need to specify 3 planes with the property. Where these 3 planes intersect will align with the mouse cursor when placing the family in a project.

There is also the Wall Closure and Scope Box properties. Wall Closure specifies where the wall will wrap in a door or window family. I never use this property since I use drafting views when detailing jamb or sills. I’m not sure why scope box is there you can’t create scope boxes in the family editor.

Here are some more tips to make sure your families are stable and flex properly:

• always lock geometry to reference planes, labelled dimensions should always connect to planes not geometry.
• when constraining ref planes with EQ, create the ref planes at equal distances.
• when drawing ref planes the left side is always positive. The name always appears at the end point.

That’s it for this week. In the next few posts I’ll cover reference lines, controls, nested families and auto-dimensions.

I should be back with an Revit related post next weekend.

This is a topic filled with mystery and confusion. Partially because Revit doesn’t let you see the coordinate system like AutoCAD does (and most Revit users are ex-AutoCAD users) but I think the main reasons are poor documentation from Autodesk and really bad tutorials or explanations on the web. When I sat down and really looked into it I found it simple and easy to use. It’s just a matter of explaining it in a way that lifts the veil of mystery and lets every see how the machine underneath works.

AutoCAD coordinates

AutoCAD use a Cartesian grid called the “World Coordinate System” (WCS) to know where to place all objects in the file. This grid cannot be changed by the users. AutoCAD also has a “User Coordinate System” (UCS). This is another Cartesian grid that the user CAN change. The user can move and rotate the UCS anywhere on the WCS.

Revit coordinates

Revit has 3 grids systems. The Project grid which acts like the WCS and also the Project Internal and Shared coordinates which act like the UCS. Until version 2010 the only way you could see where 0,0,0 was in Revit was to import a cad file using origin-to-origin. With 2010, came 2 new features: Project Base Point (which shows the location of the Project grid) and Survey Point (which shows the location of the Shared Coordinates grid). Both of these features are hidden by default. To make them visible in a view go to the “Visibility\Graphics Overrides” setting for a model view and look under the “Site” category. Their default position is on the origin of the Project grid.

Project Base Point shown selected.

Project Base Point (PBP)

The PBP is just a blue circle with and ‘X’ in the middle. When you select the PBP additional information is shown including it’s location on the Shared Coordinate grid. Also displayed is  a paper clip to the upper left.

Moving the PBP when clipped will relocate all the geometry and model views the same as the “Relocate project” command does. This however does not relocate 0,0,0. As you can see in the image to the left the PBP has been moved.

Moving the PBP when unclipped will change the reference for levels, spot elevations and spot coordinates only. The annotations read there position based on the PBP not the Project Internal Grid.

Moving the PBP whether clipped or unclipped will not move the SP.

Survey Point shown selected.

Survey Point (SP)

The SP is a blue triangle with a cross in the middle. When selected the SP also shows additional information and has a paper clip. The SP is meant to show an actual physical location in the real world, like a surveyors pin. Something that doesn’t move and the exact location can be determined on site. This point can be set to a linked file by using the acquire coordinates command and it is what is used to make sure exported CAD files will line up. Only one file in a project can be used to acquire coordinates so all consultants should use the same file. I’ll run through a scenario later on in this post.

Moving when SP when clipped will move the origin of the Shared Coordinate system and the linked file as well.

Moving the SP when unclipped doesn’t do anything really except change the coordinates of the SP marker. I don’t know why anyone would want to do this.

Moving the SP whether clipped or unclipped will not move the PBP. However, the PBP reports it’s position based on the location of the SP. So whenever the SP is moved the coordinates of the PBP change. This part is confusing I know but you can still get your CAD files to align without understanding this.

Note: clipped is not the same as pinned. Pinning the PBP and SP will prevent you from moving them completely.

One final crack at clarity

If your still confused I will offer this one final example using real world items.

Your sitting at a desk and on the desk is marked a Cartesian grid with 0,0 in the middle of the desk. Sitting on top of the desk is a clear glass plate it also has a Cartesian grid on it. Paper clipped to the middle of this plate is a picture of a triangle with a cross through it. On top of that plate, there is a second glass plate with yet another Cartesian grid on it. Paper clipped to this glass plate is a 3D model of a building. Moving either one of the glass plates does not affect the other glass plate.

Does that help to make it more clear. The desk is the Project grid you can’t move it at all. The first glass plate is the Survey Point and Shared Coordinate grid. If you remove the paper clip from the SP you can move it around on the glass plate without affecting the grid location. If you leave it clipped you move both. The second glass plate is the Project Base Point and Project Internal grid. If you remove the paper clip on this plate you can slide the plate under the 3D model. If you leave it clipped you move both together.

A scenario in Revit

Alright let’s do a step by step using the Big Box Blog Store as a scenario. However, I’m not going to be starting with the civil drawing like most other tutorials do. The firm I work for has a very large client with many stores. It is important that the CAD files all line up to the clients fixture CAD file. Also the building has usually been modeled in Revit before the client sends the finalized fixture layout. Which means I can’t link the fixture DWG using the origin-to-origin option.

Step #1 – Link the fixture layout into the Revit project using the centre-to-centre option. Next move and rotate the fixture layout to align with you building and pin the linked file to the location. This has been done in the image below. The text note is pointing out the origin of the CAD file, not Revit.

Floor plan with linked fixtures and SP selected

Step #2 – Activate the “Acquire Coordinates” command (Manage tab -> Coordinates panel) and select the linked file. The Survey Point should now appear when the linked file’s origin point is and it’s coordinates should read 0,0,0. In the image below, you’ll also notice the Project Base Point hasn’t changed location.

Floor plan showing relocated SP

Step #3 – When exporting to DWG make sure you set the “Coordinate system basis” on the “DWG Properties” to “Shared”. To make sure it all works open the linked DWG file in AutoCAD and insert your exported floor plan to the 0,0,0 origin. The plans should line up perfectly and so should the consultants if they all use the fixture DWG to define their origin points too.

Well that was a long post for a simple 3 step process. If you still have any questions send me an email or leave a comment on the ReVVed Facebook page.

PS – with the coming onslaught of the Christmas season I’ll be taking a break from blogging to do some serious nogging. See you next year.

Step #1 – Adding a Roof

1. Select the “Roof by footprint” tools and use the “Pick walls tool” to select the walls. Make sure defines slope checkbox is unchecked. This is because flat roofs are not defined by slope (4 in 12) but by datum elevation points that are relative to the underside of the deck (-6″).
2. Make sure roof assembly has no “variable” layers, unless using sloped insulation. Otherwise only the variable layers will change and not the entire roof assembly like we want in this example.
3. Select the roof and use the “Add point” tool in the “Shape editing” panel. Specify a -6″ elevation that is relative to the current level and place a couple points where the beams along gridline ‘B’ end.

In the images below I show the final roof layout. The elevations I show are noting the top of the roof assembly instead of the underside of the deck but you can see there is a 6″ slope. You can always reselect the points you added and change the elevation at a later time too.

The Roof Plan

Building Section

Step #2 – Adding the skylight opening

There’s not much to this step but it is important to use the “Vertical opening” tool instead of adding a hole in the roof boundary. This is because the roof slop should continue past the skylight uninterrupted. By adjusting the roof boundary, Revit will make the border of the skylight at 0″ elevation which will mess up the slope lines. The “Vertical opening” tool is applied after the roof is created and so doesn’t affect the roof slope (it acts like a void extrusion). The images below demonstrate what I mean.

Skylight opening by roof boundary (wrong way)

Skylight opening by vertical opening (right way)

Step #3 – Adjusting the roof structure

You probably noticed that the skylight opening exposes 2 joists below the roof. The architect doesn’t want these joists blocking the light so we’ll need to adjust the structure supporting the roof here. Revit allows for this without too much effort or MATH. The last thing we want to do is to be using trigonometry to calculate beam vertical offsets on a slope that is less than 2%. Well put away the calculators you don’t need them.

In this step we are going to put W16 beams around the skylight opening and then replace the OWSJ’s that run through the skylight with W12 beams. See the image below.

Final skylight structural layout

1. Add W16 beam’s to support the end of the joists at the skylight. Make sure you check “3D snapping” when placing the beams, Revit will attached the beams to the joists at wither end of the skylight opening. However, we need to raise the beams 5″ to match beam system offset which we added last week to adjust for the OWSJ seat depth. No problem, just use Z-direction justification parameter on the W16′s. Set the justification to “Other” and then set the amount to +5″. See no math required. The top of the W16 beams now matches the joists on either side.
2. Now we need to edit the beam system so the joists don’t run through the skylight. Before starting change the joist type to 2×10 joists (this will increase regeneration speed) in the beam system properties. Next edit the boundary to create a boundary hole around the skylight. Use the “Pick supports” tool to select the W16 beams and connect these lines with boundary lines to create a rectangle. When you click finish you’ll see the 2 joists at the skylight will become 4 joists, 2 on either side of the opening.
3. However something is not quite right. If you look at the section below you’ll see the 4 shorter joists come in at the default height, not sloped like our other joists. Toggle 3D constraint on beam system to return joists to proper seating, that is check the checkbox and click apply and the uncheck the checkbox and click apply again. Your 4 joists will then look like the second image below. Still not quite right.
4. Simple to fix this just unpin the 2 joists at the wall and drop end at wall -5″ again. Revit pins these joists when boundary is edited. See still no math required.
5. The final step is to switch the 4 joists to W12 and switch joists at ends of opening to W16. The you can select the beam system and change the default joist type back to the OWSJ. The joist’s you changed to W12′s and W16′s will remain unchanged.

Joists at default height

Joists after 3D toggle

Step #4 – The clerestory skylight

The clerestory skylight is nothing special. I just added four walls around the skylight opening and then another sloped roof aver the walls then I attached the top and bottom of the walls to the appropriate roof assembly and added a window in one side. One thing I wanted to point out when I attached the bottom of the wall to the main roof the insulation on the roof was automatically cut back for me by Revit. The structural layer of the wall is connected to the structural layer of the roof assembly. The image below shows the finished skylight.

The finished clerestory skylight in section

Retraction

In last weeks post, I mentioned that I would also be adding a decking profile to the roof assembly so all the sections would show this correctly. You can’t add deck profiles to roofs yet, only to floor assemblies. Hopefully, Autodesk will add this soon.

See you next week.

I’ll be using RAC 2011 for this post as I work in the architectural field, not structural. So if I miss any important structural items, you’ll know why. Why do I bother modeling the structure of the building? The first reason is; the structural engineer on this project doesn’t use Revit so I can’t get him to do it. The second reason is; between reflected ceiling plans, wall sections, building sections and interior elevations there are many views which will be showing the roof structure and so taking the time to model it means you don’t have to worry about drafting it into a dozen views later on. Remember, if your only going to see it in one view, it’s not worth creating a complex model for it.

How to layout an OWSJ system….completely.

Step one – layout the supporting beams. You don’t need to start with columns first. In fact, in this case it is desirable not to because the columns need to attach to the beams, not the other way around. This is because the beams cantilever past the columns, a trick used by structural engineers to reduce the span and thus the required size of beams. See the image below.

Roof plan

Step two – layout the beam system for the OWSJ’s. However, instead of using OWSJ, I’m going to begin with 2×10 dimensional lumber. This is because the computer can render the simple geometry of a 2×10 faster than the complex geometry of an OWSJ. Later on I can set the joist type to an OWSJ. The screen-shot below shows a section through our building. Nothing special so far, the roof is indeed flat (too flat) and the top of the structure is all at the underside of deck level where I laid it out.

Building Section

Note: when I laid out the beam systems, I used the “Pick Supports” tool to select the beams and walls that the joists would be bearing on.

Step three – lets add some slope to our roof. I’m going to add a 6″ slope to the roof with the low points at the beam ends. The first time I laid out a roof like this I would end the beam over the column and use the “Start\End Extension” parameter to set the cantilever distance. However this makes setting the slope more difficult as the “Start\End Level Offset” lowers the beam at the column point and not at the end of the beam like I wanted. It is also important to take into account the seat depth of the OWSJ at this point. The beams don’t sit at the underside of the deck, they sit below the joists and the joists sit at the underside of deck level. I’m going to use the DLH Series Bar Joist that comes with Revit. It has a 5″ seat depth. So I need to drop the beam end at the concrete block wall 5″ and the beam end near the columns 11″ (6″ slope + 5″ seat depth). See image below.

Roof framing plan

Hints: You can modify the Level Offset of 2 beams at the same time if the beams have a common end point. Just select both beams and the offset will appear at the common end. Also sometimes you will have to adjust the beam cutback when you are adjusting the level offset, to avoid the condition shown in the image below. The beams should end where the arrow indicates but a beam cutback has forced on beam back. Just activate the “Column\Beam Join” tool in the Modify -> Geometry panel. You’ll see arrows appear next to the beam ends, when you click on one of the arrows the beams should act normally. See image #2 below.

Image #1

Image #2

Step four – once the slope has been added select the beam systems and change the joist types to the OWSJ. Looking at a section through half the building (see image below) now we can see that the beam end near the wall is at the level of the underside of the deck but the other end is at the same height as the beam. This is incorrect because OWSJ’s sit on top of the beam. To fix this select the beam system and add the seat depth (5″) to the elevation parameter. Now the OWSJ’s sit on top of the beam but the end at the wall is 5″ above the underside of deck level. Still not quite right. The last step required is to select all the OWSJ’s in the beam system, unpin them from the system and deduct 5″ from joist level offset at the wall end. Looking at the section again shows the OWSJ’s now slope as they should. See image #2 below.

Image #1

Image #2

Note: It is more efficient to wait until the end of step four to change the joists from 2×10 to OWSJ’s. Even this little project took a minute to regenerate when the beam system slopes were adjusted.

Step five – add the columns. Just drop them at the grid line intersections and then attach the top to the beam above them and the column height will adjust automatically to reach the bottom of the beam.

That’s it for now, next week I’ll put a sloped roof assembly on the OWSJ’s and show how to add a deck profile so all your wall sections show the metal deck without having to draft it in after.

PS – if anyone wants a copy of the project file I created in today’s post, send me an email.