True Perspective solution needed please.

[Guitte]

Good day,

 

Any suggestions on how to work out the true perspective of a glass segment on an 33.8 degree angle? I did try on the right-hand side, get stuck thereafter.

 

https://www.dropbox.com/s/zs02ahi0ys9ozr8/Zone-F%20try.dwg?dl=0

 

Thank in advance.

Guitte

[SEANT]

I don't know enough about glazing to get a good picture of what it is you are trying to do, based on the contents of that drawing. I do know that a couple of perspective transformation option do exist; do you have a Ortho view of that layout?

[Guitte]

Hi Seant,

 

No, we only have these two views. We have here the Top view of a Cone, with 1 side view demonstrating that the panel is lying on a 33.8deg angle. What would be the true view if i looked at the panel on a 90deg angle. The problem is that all 4 ends of the glass panel has each their own angle. I need to apply trig without a 90 deg reference point and still today i struggle with it. To make it a bit easy i tried to construct the true view of the glass panel and not sure if that is right.

 

I'll add another view. So it can give perhaps more clarity.

 

https://www.dropbox.com/s/zs02ahi0ys9ozr8/Zone-F%20try.dwg?dl=0

 

Below is what im looking, not sure if my construction is correct.

Please see second page on presentation.

 

http://www.google.co.za/url?sa=i&source=imgres&cd=&cad=rja&uact=8&ved=0CAgQjRwwAA&url=http%3A%2F%2Fwww.slideshare.net%2FVivekSricharan%2Fist-year-engineeringgraphicsedforbestudents-1-1&ei=8pWLVfC2LMqf7gbDo5rYDQ&psig=AFQjCNFsHa0zx47Zc2Bnpoeh6Hw6fqEAkw&ust=1435297650816295

Edited June 25, 2015 by Guitte

[SEANT]

If I had to guess I'd say that the "top view" is actually an auxiliary view - aligned to the first rafter and (hopefully) the fist run of trapezoids. If that is true then the first run of traps should be actual size, the remainder would have some off angle induced distortion. What is your ultimate objective; a different drawing view, or the true shape of each segment to prep for fabrication?

[Guitte]

We need to work out the true shape of each segment to prep for fabrication.

[SEANT]

Unfortunately, the corresponding angles of the trapezoids do not match so the view is not aligned to the first row (i.e., the traps are probably not actual measure).

 

Your first assessment is probably correct. The actual sizes will have to be derived either by Trig, or modeling the geometry in 3D to get the correct dimensions.

[Guitte]

https://www.dropbox.com/s/zfd42klr75zaua1/Zone-F%20try%20%282%29.dwg?dl=0 - Think your right, the side glass doesn't line up with the glass next to it (R1-A1 with R2-A1) best would be to ask Pythagoras. Have to divide the trapezoid into 4 angles to get a right angle.

[SEANT]

The geometry in the attached file will look confusing, but the file demos a down and dirty 3d method for deriving the shape. See the yellow geometry.

Zone-F try_3D.dwg

[Guitte]

Thank Seant, if you see my latest attachment you will notice that each beams angle is different from the one next to it. R1 = 33.8deg, R2 = 33.5 deg, R3 = 32.70deg at R12 = +- 54deg. I really appreciate your input. Inventor would have done a great job... unfortunately don't have it.

[SEANT]

Sorry. I was still assuming the original drawing had the auxiliary view aligned with at least the first rafter.

 

I'll bow out now - I do not have sufficient insight into the project.

[Guitte]

No need to be sorry Seant. One of the things was to find out if my construction to get true view of the panel was correct. At school things didn't make any sense, cause you don't know where to use it in practice. Now the practice comes and no teacher... Luckily we have a forum.

[steven-g]

Is this drawing the true plan, because your original question is about perspective, it looks like the drawing could be of a perspective view. But is this in fact the actual shape of the construction so that everything is off center. And out of curiosity what is the material being used, it looks like tubular section

[Guitte]

Hi Steven, what i needed to know and actually all i wanted to know was how to construct a trapezoid's true view (in this case the glass).

Is my construction on the drawing the correct way of doing?

 

This is meant to be off center. The support structure is tubular steel with the glass on top. Not sure what the spec's are though.

[steven-g]

The attached drawing isn't using your data, it is just an example of how I would go about creating the true glass shapes from the given details using geometry theory, I would suggest trying it out first before issuing details and getting hundreds of glass pieces made. Ideally you should have access to a 3D drawing to make this kind of work a lot easier. And if I have made any glaring mistakes hopefully someone else will point them out.

trapezoid.dwg

[Guitte]

Thanks Steven,

 

Sorry, Im lost with your drawing.

[steven-g]

Sorry about that, just spotted that the second sketch didn't actually point to the end of the lines, as I intended it too, does this make it any clearer, I added the first panel from the bottom left hand corner of your drawing.

trapezoid2.dwg

[Guitte]

LOL, better. It somehow makes sense. You took the top view panel (884mm) and add the true width of the panel in diameter, which is r = 1063. You have added a perpendicular line in and just stretch 884 perpendicular to the edge of the circle. On your sketch is the top view 1063mm now the true view of the panel, right?

[steven-g]

On your sketch is the top view 1063mm now the true view of the panel, right?

It's how I would do it, as I said you really need someway to verify that it is correct before you start cutting glass, as the only sure fire way of doing this is drawing it in 3D, or making a mock up.

[tzframpton]

I have to side with SEANT in his advice to approach the design first in 3D, then you can select any view you need from any angle and produce accurate perspective-based views. If not on this project, then the next one. SEANT is probably one of the most talented individuals when it comes to mathematical and trigonometrical CAD processes.

[SEANT]

Thanks Tannar. Very gratifying to hear an industry power user acknowledge my efforts.

 

If I were given a similar task as presented in the original post, I would definitely addressed this with 3D geometry. It's just my 'Go To' methodology.

 

The problems posted here at CadTutor, though, present great opportunities to keep the old mathematic/trigonometric brain matter active. So, in following the footsteps of steven-g, here is another possible 2D way of re-expanding the truncated geometry. A bit confusing I know, but see if the attached recreates the proper dimensions. If it works, the geometry can be converted a full rafter run at a time.

ViaBlockScale.dwg