Hi guys, I can hear the groans when I mention geometry, but how else are you gonna solve this problem
Take 3 sides of a triangle with sides say 3.5,4.5,5.5 unit lengths.
Try to draw that in su and most know, you cant, because of the limitations of segmented arcs when trying intersect the sides. Even using the highest resolution 960segment per circle it wont join properly with accurate sides.
You can’t for example create a polygon with a defined side length. Try drawing a pentagon with unit side length
AFAIK this limitation is the same for 2016 and this is not a criticism, its the nature of the beast.
Some years ago I put together the algebra equations to solve this problem (groans), intersection of 2 circles (2d) and 3 spheres (3d) and made it all work on excel. Complex and fiddly but just high school maths
So I punted this to the community asking for someone to help turn my equation written in simple pseudo code into a Ruby app for everyones’ benfit, but got no offers
I’m hoping in 2016, given the amount of clever extensions out there that someone will see the value of this little tool
As we all know, accuracy is essential in su, you can’t be near enough, its not good enough and erros left in your model have a habit of propagating and you cant get faces to fill properly. Trying to fix these minute errors in an advanced model retrospectively is a ball breaking task
Sorry guys but the arc tool is the same old segmented circle and wont give the right point of intersection for a true circle and this is where you can be caught out. Note I have measured the true length of the sides, not the radius of the arc tool (3.5 and 4.5)
tried trilateration, but its buggy doesn’t work for me though I did find the manual eventually, uses cosine law and , if it worked, may not be accurate to 13 places?
TIG true tangents doesn’t do anything, no instructions
SUCCESS! After going thru the fiendishly difficult process of creating a Trimble account, I was finally able to download the Skema survey app
and it seems to work great simple to use and seems accurate AFAIK
the perfect tetrahedron. If anyone can tell me how to post a .skp file here I’ll be glad to share. (wonder why Trimble doesn’t want us sharing models?)
Each of the 6 sides is exactly 1.000000
It was done using Skema
If anyone is interested I’ll post details, but it involve constructing the height triangle (using Skema)
to get the height line then moving it to the centroid of the base. The rest is done by copy base and rotate (see the height line I made at the top of the pic
That draws the five regular Platonic solids, specified by either edge length or radius of enclosing sphere. You can edit the size subsequently as well.
Hre is link showing some of Paul Bourke’s work Starting on page five is on intersection of a line and sphere ( or circle) you should find helpful. http://paulbourke.net/geometry/circlesphere/
thanx Mac, that link has pages 8,9 which show the algebraic equations for the intersection of 2 spheres and gives a circle, then use intersection of 2 circles on that to get 2 +/- points in space for the point in space required from 3 vertices intersecting, qed.
I am sure I ought to be able to do this with the Skema tool, will revert
Hmm; I just clicked the link above, it does not show page# but when you try to print it shows 28 pages. The part I though you would find of interest is the line 3 d sphere part but was not expecting any action on your part just FYI. It was published in 1992 and can be useful for problems like you noted.
