Spiral Ramp using Tube

[Anonymous]

Hi,

I have created a object that creates a spiral ramp. Ie it rotates around a centre point and increases in height. I am using the tube command to do this.

I have 2 parts to my question/problem

Part 1: My problem occurs with the vertical edges. The vertical edges appear as though they are curved, curved in elevation as well as in plan? I have had a look at the inbuilt ArchiCAD objects that use tube and they do not seem to do this? although i am sure i have seen it happen before with another object a while back. Any suggestions. I have tried upping the number of segments of the curve but it still happens. Anyone else had this problem?

Part 2 to my question is has anyone used any other objects to do this. I have noticed their is a inaccuracy with the tube object as it slightly deforms the profile along its length?

[Anonymous]

if you have the cookbook there is a section on spirals & helixes i think that you may be better of using the prism command rather than tube if you a requiring a profile that is rectangular in section

[Anonymous]

Mark,
I have used BPRISM_, TUBE, and TUBEA for this purpose.
I have found that BPRISM_ to be the easiest to code
because you don't have to define a path and the smoothness
is controlled with a resol statement.
Peter Devlin

[David Collins]

Mark wrote:
The vertical edges appear as though they are curved, curved in elevation as well as in plan?

I have seen GDL objects created with REVOLVE and TUBE appear oddly smoothed in OpenGL. Is that what you're seeing? In TUBE, the status values of the profile nodes control smoothing. 1 smooths the tube, 0 doesn't. Maybe you can switch off the smoothing of the ramp sides? Not great, because you'll see the vertical line at each step of the tube path.

The Cookbook does conclude that the bPrism method gives the best rendered appearance, but it sure is a twisty approach to the problem.

[Anonymous]

Thanks guys, seems like the bprism in the cookbook might be the way to go, i will give that a try.

[Rob]

I have found that BPRISM_ to be the easiest to code

well, that's right but it is not going to work for a spiral ramp, actually I should say it works with a great limitation because BPRISM_ command has got an internal relationship defined for the height and radius: radius must be always bigger then height...
attached screenshot

[Anonymous]

Hello Rob,
I don't understand why this would be a problem.
If you want a very tight spiral just make "H" negative.
Maybe I don't understand what you are saying.
Peter Devlin

[Anonymous]

I should have shown the dimensions this way.
Peter Devlin