someone asked me how i evenly rotated and positioned the three cannons on the Haxor Outpost 78-369 and i should have answered with a blog post for anyone else wondering
things are already square enough in the virtual worlds when you build everything out of prims and i tend to take the easy way with rotated things such as the cannons on the outpost. it’s faster and easier just to make four of them at 90 degrees from each other than to rotate them 120 degrees to have three of them. since the cannons are sitting on a central command sphere, their placement should, ideally, be spot on as far as x and y coordinates go
i’ll illustrate how to do “uneven” rotations yet end up with everything placed to the exact pixel. to show this, i’ll do it with five arms from the base to the chair i made yesterday as a freebie
many office chairs have 5 arms with casters as their base. for OpenSim, it would be easier if it only had four (like in the chairs i made two days ago – the economy models) but five is what real one has and that’s what i wanted this fancy chair to have also
just like the cannons, you make one complete object and in this case that would be the radial arm, the vertical cylinder holding the pivoting rod connected to the casters, and that caster itself. for the sake of the illustration, i removed the caster. make whatever it is as complete as possible, including texturing so that you don’t end up trying to place something by eye or needing to shift select a bunch of parts for texturing
next rez out something that sits in the exact centre of the final build. for the cannon i used a tall plain box positioned at the x and y of where the command sphere would be and for the chair it’s the centre post that the chair’s pneumatic cylinder sits in (the air thingie that makes the chair go up and down). it helps to place your centre object on whole numbers as far as x and y coordinates go. now i shift duplicate the complete arm and rotate it 180 degrees and place it opposite the original at the exact same distance from the centre post as the original. now i link them together with the centre post being the root prim
you can see in the pics that the “extra” arm is just plainly textured so that i can easily tell it apart from the final ones
here’s comes the uneven math rotation. i want 5 arms so i divide 360 degrees by five and get 72 degrees – that’s what i’ll need to rotate each arm in order to get five evenly spaced ones
now i shift duplicate the entire assembly and ctrl-z it back to where it was without unselecting it. then i type 72 into the z rotation field in the edit box since the centre object is a cylinder (using something like a cylinder or box with zero rotation as a temporary centre point keeps this math easier)
then i repeat that to make the other arms and to keep it simple, i keep duplicating the original one – the third arm would be 144 degrees (72 x 2), the fourth would be 216, and the final one, is 288 degrees
now you see why i colour coded the parts because there are a total of ten arms but only five have the correct positioning. now in unlink the whole thing and delete all the default textured parts and i am left with 5 chairs arms perfectly placed. you should leave one centre prim or add one back in so that you can link it all back together with it as the root so that you can precisely place it in your build
this is pretty easy and beats the frustration of trying to eyeball angles and positions =)
variation: you don’t have to duplicate the object and place it opposite of the original one, you can simply connect your built part to a root prim that is in the centre and when you rotate the duplicated one, just type it the x and y coordinates of the original to pop it into position
did you miss the weekend chair posts but need some office chairs? get them at enerhax.com as freebies =)
one “arm” with centre post
duplicate arm placed 180 degrees off and same distance from centre
shift-duplicate and then ctrl-z
rotate by 72 degrees (or whatever you need)
repeat and rotate in the next multiple needed
fourth out of five arms and why i colour code them
if i used 60 degrees and one more arm, i could have a cool 60′s retro atomic clock! =)
delete the “extra” parts and voila!
from prim to chair without getting too dizzy =D
You are a very nifty builder ;D
Eros Deus
16 Jul 12 at 2:55 pm
To think, all of this could extra dancing around be solved with the introduction of definable pivot points! That, along with definable parenting are my two biggest wishes for object enhancements in Opensim. The rest of the list is about a good meter long and gets progressively sillier as it goes.
ATupper
16 Jul 12 at 3:16 pm
I could swear one of the viewers lets you rotate from a point or the end of a prim… I forget which! I just do it the way Ener does.
Azzura
16 Jul 12 at 3:32 pm
Nifty Trick, I’ve used a similar method in the past when making Circular garden sections.
I always thought there had to be a better way.
Hey Ener, do you make use of Qarl’s Align Prim Tool?
Techplex Engineer
17 Jul 12 at 6:37 am
I use a similar method. To use your objects, Ener, here’s what I do;
Create the caster, arm, etc and link as a set, but without a center post.
Position so that the co-ordinates are whole numbers. Easy to remember that way.
Shift-copy enough to fill my needs.
Link the first to a center post, then rotate the required amount, 72 degrees.
Move the next back into those easy-to-remember coordinates and link to the post.
Repeat until you have the base.
As a side note, how many of us told our math teachers “we’ll never use this stuff”? *laughs*
Sarge Misfit
17 Jul 12 at 1:07 pm
i’ll try your technique Sarge, i think it would save me a step =)
i love Qarl’s tool but am not in the habit of using it
Al, it sounds like you may be talking about mechanics? that would be awesome to have in OpenSim – then you could make real machines =)
Ener Hax
17 Jul 12 at 2:59 pm
If I recall, OpenSim has Ninja physics which uses actual joints, such as for hinges. (checks INI files) yes, there’s a setting in the Joint Support section of OpenSimDefraults.ini
I’ve no idea why its not used.
Here’s a link to OpenSim’s Wiki entry: http://opensimulator.org/wiki/NINJA_Physics
Sarge Misfit
17 Jul 12 at 6:39 pm
holy crap Sarge! i really do live under a prim! awesome link, thanks!!! =)
Ener Hax
17 Jul 12 at 6:45 pm