Mini-challenge
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@tig said:
Mac1
How do you get the rotated guide pt to snap exactly onto the horizontal top guideline ?
The guide point and the guide lines are rotated ( their 3.5 spacing is used to get the intersect point on the post A bottom. The post B top is used for the snap ref. Have to do that since you cannot inference to guide lines. The error can occur on the other end when trying to get the guide point on the line. If you what more accuracy one could use the technique Jeane uses for interpolation to come close to the intersect point when rotating one line into another.
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Yeah, that's essentially the same thing I did, but the reason I didn't make a circle is the circle geometry is too imprecise to work accurately in every scenario.
I'll check out TIGs latest when I get to the studio.
Best,
Jason. -
This is the simplest non-plugin way I can think of - it's much less hassle than my last attempt...
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@dave r said:
That stuck with me, too. I can't remember who I took to prom, though.
Your wife will be pleased to read this. -
Looks like use of a centerline to start is not a good idea?
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@tig said:
This is the simplest non-plugin way I can think of - it's much less hassle than my last attempt...
That's what gilles came up with.
http://forums.sketchucation.com/viewtopic.php?f=15&t=44972&start=90#p401988however, there's a slight shift in the angle of the long side, so technically, it's not precisely tangent to the 300mm circle that would be drawn at the start point.
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Another tricky Tig method with always fantasy of temp crutches
In theory the more elegant is the rotation method : one circle / one rotation
It's like this that nurbs programms do
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SU does not manage angles under 0.001° in rotation, another frustrating inaccuracy.
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Gilles and TIG,
This method is not precise. I've added a "true tangent" to where the corner of the board should be, and if you zoom way in, you can see there is an imprecision there.
if you zoom in to the corner, you can see how it doesn't exactly match the true tangent.
Andy
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@tig said:
This is the simplest non-plugin way I can think of - it's much less hassle than my last attempt...
Unfortunately it's not accurate either. It's "just" an approach like all other attempts before. If you were to measure along the long edges(true distance between long edges) instead of still using the already existing dimension (300.000000mm)you can see that it is still less than exactly 300mm. After rotating the short 300mm edges on both sides towards the respective Clines, these Clines by themselves aren't perpendicular to the long edges anymore. So you need two new Clines and rotate the short edges again, and afgter that again etc. You'll get closer and closer but to quote Jeff: "no sigare", for it isn't 100%. SU can't do it with its native tools.
SketchUp simply lacks the true (construction-)circle and unfortunately does not snap an endpoint A (of a rotated edge AB) to another edge CD (unless the edge's other endpoint B is already on CD.
As you said before, Your "true tangent intersection" and also (I'll take his word for it) Jeff's DC are the solutions to go by.
SU-team (now that you're not caged by Google anymore) please, it's high time for a construction circle tool to solve these issues. -
TIG, I have to say, your true tangents ruby is thanks again!
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OK, I broke down and looked at the math on this -- it seems dirt simple to do so I think this is the solution (based on the math).
In this instance the desired width is 2 inches.
Best,
Jason. -
This is not perfect, sorry.
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This started as an exercise in drawing something using only SUp's native tools that is actually impossible to do to 100% accuracy; however, it can be done manually to a reasonable accuracy.
You are of course right, in that the width of my 300mm rail when adjusted using my methods is in fact 299.982273mm [the ends are still slightly skewed to the long sides!], but since that 0.0177mm is much thinner than a human hair and only about 1/3rd of the thickness of a Rizla cigarette paper [approaching the limit of human visual acuity!]... and we aren't [usually] designing nanobots or sending someone to Mars - all of these simplified approaches are usually adequate. For how often might we expect to find a piece of wood exactly 300mm wide - even when measured with some uncommonly accurate gauge ?
Repeating this process twice does get even ridiculously closer, but with little benefit...
My True-Tangent's - True Intersection tool will give the best result, but we should also not loose sight of the fact that since trigonometry/geometry uses 'irrational numbers' in its sines/cosines/square-roots etc the result of most angular rotations of points cannot be be determined with absolute accuracy either - but it is just close enough that it will report for all intents and purposes as the expect values ! If you made the same 300mm rail using True Intersection it would measure in the SKP as 300mm exactly - although in fact it's maybe ±0.0000001mm off too - but Ruby and SUp always rounds answers to suit themselves - just as SUp will do if it ever gets built-in tools to do this.
This all said, I do agree however, that some simple native guide-arc tools would be very useful so that we might find the intersection of two arcs without using convoluted calculations as used in my toolset...
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There is an oddity where if you measure the ends it is correct but if you measure the middle sometimes it will not be, I'm not sure why...
What I don't get is I entered all values into the VCB -- thus taking any accuracy issues out of my hands... 90 degrees should be exactly 90 degrees and 2 inches should be exactly 2 inches. The only way I can see this not being true is if the inferencing engine is not precise -- and if we can't trust that, then can we trust anything?
Either Pythagoras is wrong or SketchUp is: http://www.mathopenref.com/rectanglediagonals.html
Best,
Jason. -
Yeah, no doubt -- yesterday I came within 1 micron of perfection... that's some pretty ridiculous tolerance for a crossbeam.
But the concept of cumulative errors building up over the course of a drawing is disquieting.
Best,
Jason. -
Clever solution Fredo !
Well done.
I agree with you that a fully accurate non-plugin solution is just not possible.
You can get accurate enough for most purposes, but to do it properly needs complex calculations with sines/cosines/tangents/PythagorasTheorem etc... so it has to be done by a plugin-tool or a [new/changed] native tool.
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