New slab tool -- watch those points!

[Wes Macaulay]

When you add new points to a slab object in RAC2008:

choosing "Relative" means relative to the elevation of the slab wherever you place the point. It is not related to the elevation to the top of the slab, or project or shared coordinates
clearing the "Relative" checkbox means the elevation of the point being entered is project coordinates
But when you edit these points, the elevation shown for the point is relative to the top surface of the flattened slab. So the values are different between when you add them, and later when you edit them! This doesn't make sense.

This is in the documentation under Structural Tools > Shape Editing for Slabs Roofs and Floors, but worth noting in advance...

When I add points, I don't want to think about the point's elevation relative to the current slope of the slab ("Relative" mode, and I definitely do not want to work with project coordinates either)... I want to think about its offset from the original top of the slab. So I'm entering all points as 0 Relative, then going in on the next pass and editing the points with respect to the height of the top of the slab. What do the rest of you think?

[jeff.95551]

I'm not sure I completely get you - I've used this tool extensively already, and love it. I start with a sketch, locate where I would want the points and how high they should be relative to 0 (the original top of the slab), and use the slab tool to put them in. It works pretty much like the topo tool, I think. I always want to use the slab insertion level as 0 and build or drop from there. The only way I can think of to improve it is to have a slope annotation family - then I could totally wing it and still know I was good.

Jeff

[Wes Macaulay]

Draw a slab and edit some points -- say a point in the middle that's down 1'. Put then a new point down right beside it -- it will be down another 1' from the first point! I don't think this is good behaviour at all.

It's not adding points based on the top of the slab -- it's adding them relative to the height of the slab wherever you're clicking. So if you place one point at -1' relative, then one riiiight next to it at 1' relative, it will be down -2'.

But when you edit the points, they show their numbers not relative to each other, but relative to their height from the top of slab.

Check out the section: the points were both set to -1' relative. The first point goes in, then the second goes in 1' lower.

[Brian Myers]

I agree Wes, this seems confusing. I wanted to demonstrate this feature in a recent webinar with multiple points and found myself during practice just not being comfortable with it. In the end for simplicity I just demonstrated a single point (which was good enough) because placing points the way it defaults just didn't feel intuitive to me yet. Don't get me wrong, I love the feature, but how it goes about placing these points doesn't follow the workflow I would expect (it really threw me the first time I used it, it took me a couple seconds to realize what it was doing).

[jeff.95551]

When I use this tool, I work in one of two ways -
First, since I'm working from sketch, I add all the points at 0, then go back and modify them at the point, or

I put a number in the elevation box and UNCHECK the relative box. The relative option adds too much uncertainty - if I'm adding a point at -6" at some point along a slope, how do I know exactly what the height was before and what impact that's going to have...

And I certainly wouldn't want it to try to list the heights later in some 'relative' way. The only way to understand the elevations is relative to some common datum, which is the floor's insertion point. Is it going to tell me relative to what the elevation was before I inserted the point? What happens after I move a different point and change all the dynamics? That would be like trying to manage elevations on a waterbed - push down in one place and everything around it moves. I don't know that that would be a great process... I vote for leaving it the way it is.

Jeff

[dfriesen]

Draw a slab and edit some points -- say a point in the middle that's down 1'. Put then a new point down right beside it -- it will be down another 1' from the first point! I don't think this is good behaviour at all.Very good point, Wes, thanks for the head's up. The behaviour should be that new points are placed relative to the defined floor height.
I guess in the mean time till they correct that, the way to do it is place all your points at 0'-0", then edit them. Any new points after that will then have to be adjusted. At least we can select a bunch of points in edit mode.

[Wes Macaulay]

Jeff, what you're asking for is to have the "Relative" checkbox (when adding points) reference the elevation of the top of slab. That's what I'm asking for too. I want the elevations I'm entering when adding points to be the same when editing them. Currently, they're two different numbers.

[jeff.95551]

Gotcha! Without knowing it, I've gotten around this by doing the first method I listed - add all the points at 0'-0", then go back and modify them, which gives you the correct readings without the confusion, or by using absolute elevations. I just haven't worked that way to be frustrated by the process. So you're not asking them to change how the points are listed after they exist, only how you put them in... I'm with you - relative should mean relative to the floor's base level, not to some indeterminate already modified point...

[patricks]

Hmm I guess that explains why I was getting all those add taper lines on my slab when I was trying to draw a depressed slab.

What I've been doing is instead of placing points, I'm drawing lines (one of the other floor modification tools) where the lower area of my depressed slab occurs, and then setting those lines at elevation -2" or whatever, and then I'm able to get the desired results.