mini-challenge

[TIG]

VERY clever Pilou !
Bravo to you too.

Here's my slight reworking of your brilliant ideas, with some explanatory notes.
I think this way is a little simpler and easier to see what's happening.

[pbacot]

In the example, why push pull up on the face? The whole point seems to be to find Point 'B'. (diagram THAT clause )

Maybe this is beyond my maths. True: the center cut line in the first picture does describe the center of the final board, call it point 'X'. B is a right angle from 'X' but it's a right angle from the board's diagonal, not from the final axis of the board. Still it lies on the edge of the board a distance d/2 from point X?

brace - 1.png

[Pilou]

@TIG
Cool but there is a little mystery
In your file (from the mine modified) tichkness is not 1.000000m but 0.997509m
CD = 1.320818 m
Or you don't change the drawing and just type the text's explanations for only the theory?

In a nurbs modeler with the Technic of circle (first example of Jeff video) (with of course sames measures)
CD = 1.3239127 m & angle 40.945192°

The adventure is not finished!



File nurbs format 3dm

[pbacot]

Gilles,

I Have no idea how you figured that out One snaps to a line that is not there until the execution. That's wild!

Peter

[gilles]

Good try but...

[TIG]

Pilou's version appears to work...
But when I reproduce it there's inaccuracy again
Logic [initially] says that offsetting [pushpulling] a face that is coplanar with the known diagonal by width/2 and then adding the new sloping lines through the points ought to make them along the rail's raking edges ???
BUT the offset is perpendicular to the diagonal NOT the rails sides !
Hence the errors... very much like all other approximation methods

[pbacot]

TIG,

To me the problem is that d/2 should be measured perpendicular to the final edge, not the diagonal.

Peter

[TIG]

TIG,

To me the problem is that d/2 should be measured perpendicular to the final edge, not the diagonal.

Peter

Exactly right - I was adding that to my last post as you posted...
The difference between offsetting the diagonal and the sides is the error.

[andybot]

Gilles,

I Have no idea how you figured that out One snaps to a line that is not there until the execution. That's wild!

Peter

Indeed - components interacting with each other during manipulation has always been baffling to me. Some things work and some don't (for example try to move a line in a mirrored component so that it's on the mirror plane - it won't snap to the other side, it'll just keep going past the mirror plane)

[TIG]

I have yet another 'drawn' solution...
I can't fault it... but then again... you might...

[bmike]

I have yet another drawn solution... I can't fault it but then again...

that appears to work... instead of copying the line up by the thickness of the brace, i +rotated about the center of the original line 180d. then traced over everything to get my shape.

except, when i use the tape, with 0.000000 accuracy, i get 5.995197, instead of what should be 6" in my example.

copying the bottom line up 6" (2x the measurement i used for 1/2w) should yield better results, but then i'd guess that the top or bottom would be off. or the rotate tool is inherently inaccurate.

[gilles]

I Have no idea how you figured that out One snaps to a line that is not there until the execution. That's wild!

The line was not here but exist so you can interact with, I use this technic frequently.

[Rich O Brien]

A slight variation on TIG's

http://www.screenr.com/7VC8

[TIG]

I have yet another drawn solution... I can't fault it but then again...

that appears to work... instead of copying the line up by the thickness of the brace, i +rotated about the center of the original line 180d. then traced over everything to get my shape.

except, when i use the tape, with 0.000000 accuracy, i get 5.995197, instead of what should be 6" in my example.

copying the bottom line up 6" (2x the measurement i used for 1/2w) should yield better results, but then i'd guess that the top or bottom would be off. or the rotate tool is inherently inaccurate.

Move+Ctrl to copy the bottom long-side lines up to 'T' [as there are two lines, split by the width/2 perpendicular line...] moved up to the top of the right-hand post [T]...

[TIG]

A slight variation on TIG's
http://www.screenr.com/7VC8

Another working solution [I think!]... but it uses a script

[Rich O Brien]

A script that should be a default tool

If only Google accepted sketchUcation's offer to buy Sketchp that time

[TIG]

A script that should be a default tool
If only Google had accepted SketchUcation's offer to buy Sketchup that time

I know... I know... but we are now all Trimblers-in-our-boots

[pbacot]

I have yet another 'drawn' solution...
I can't fault it... but then again... you might...

Without doing a test, I don't see the logic that when you rotate the line back up, that point E hits the diagonal at any meaningful (or snappable) point. It can't be hitting the 'M' midpoint of the diagonal... therefore it isn't width/2 off the true axis of the board. In fact, isn't the angle created the same as measuring width/2 from M to the bottom edge?

[TIG]

That's was the point... you snap it to M but E can never 'touch' it - but it will align... landing on the centerline.
BUT... you have me 'banged to rights' - it doesn't work as it's not an exact fit, so there is still a tolerance issue
Back to the drawing board...

[driven]

been watching with no spare time...

my solution, two instances of square component, the second moved to top of target post and rotated 180º, then in edit mode rotated again from pivot point and snaped to first instances [also rotating] none pivot corner.

2012-05-03 12.10.11 am.png

john

[TIG]

Driven

I think this a variation of the two-instance-rotation-with-mutual-snapping solution posted earlier today...

Can you elaborate...

So far, I think that is the only good way [along with Fredo's weird snap inferencing example] ???

[driven]

Tig,
your most likely right, I haven't had a good look at all the 'solutions'
I'm working 18hr days at the moment and just had a quick shot at it, needed a play before sleep...
john

[mac1]

mini__mac2.skp

Here is improved on solution I posted early and all dimension have been verified to SU 32 bit float accuracy against the close form solution I presented above.
Note I have been using some of the post dimension Jeff posted early of 96" post height, 65" spacing and 3.5 rail width.
No plugin is used.
I did use the technique I posted almost a year or so ago on the exact solution of sphere line intersection.

[andybot]

mini__mac2.skp

Here is improved on solution I posted early and all dimension have been verified to SU 32 bit float accuracy against the close form solution I presented above.
Note I have been using some of the post dimension Jeff posted early of 96" post height, 65" spacing and 3.5 rail width.
No plugin is used.
I did use the technique I posted almost a year or so ago on the exact solution of sphere line intersection.

Hey Mac1 - what "sphere" are you using? It's not clear in your model what your steps are.

[mac1]

mini__mac2.skp

Here is improved on solution I posted early and all dimension have been verified to SU 32 bit float accuracy against the close form solution I presented above.
Note I have been using some of the post dimension Jeff posted early of 96" post height, 65" spacing and 3.5 rail width.
No plugin is used.
I did use the technique I posted almost a year or so ago on the exact solution of sphere line intersection.

Hey Mac1 - what "sphere" are you using? It's not clear in your model what your steps are.

Sorry did not make my self clear enough for you. At the bottom right I show the intersect point, at the bottom left I show the center of the sphere. Since SU is a 3d program any time you talk about intersecting a rotated line with a target line it must be on a spherical basis. There was no intent to show a sphere but the math basis must consider that or you do not have a closed form solution. SO the directed line segment from the line rotation point ( aka center of sphere) to the intersection of the target line( used as ref for guide point) is the points one needs to get the angle of rotation and the intersect with the rail width to the left post. SO the intersect ( guide point ) at the target line, the two 3.5 inch spaced guide lines are all rotated to the top of the left post to establish the points needed to draw the 3.5 rail to the proper points. Here is a screen shot of the skip file I posted some time ago.

SPHERE LINE INTERSECT.jpg

[mac1]

Fence truuth.jpg

BTW you need ground truth to know if your model is correct.
I presented the closed form solution for the 2d case above. Here is the excel results to check my model'

[Ecuadorian]

The fact that this thread is already 19 pages long has made me seriously consider learning either MoI or Rhino.

[Pilou]

Take Moi : It's the SU of Nurbs against Rhino !
Less powerful functions but it's not the same spirite!

I don't abort to find a more easy answer at this damned problem of align rotation who fail at mini micro sub-atomic snaping!

[andybot]

BTW you need ground truth to know if your model is correct.

Clear as mud

You still don't show your steps. I'd love to see the "sphere" you are using, or are you just talking about calculating and not modeling. Sure, anyone understanding basic trig can calculate the length of the edge based on the diagonal, that's been done a few times in this thread, but entering numbers seems to still end up with rounding errors in SU...

[CHARLIE__V]

Greetings all,

A few months back I had a similar conundrum..........after fussing a bit I just "eyeballed it" to get my cross bracing.

"Knowing" the challenge, I have taken another swing at it...........though it still does not "zero out".

In short.........center the cross brace and scale it's "ends" to meet the vertical(s).

Sorry..........I do not possess video skills.

Best,