# simple unit calculation? anyone know?

i’ve been using blender for about 2 yrs now and just barely thought i’d dig into more precision modeling. hence the following questions.

is there a simple way of calculating units/inches/??

i use both blender3d and sketchup.

both are awesome programs. currently i’m working on an arcade joystick. modeling the buttons is extremely easy in blender. however, when it comes to the measurements is when it becomes bad.

button.

for instance, the diameter of one of the buttons is 1.06inches. i understand that blender uses an arbitrary unit system. so i tried using this system to create my buttons. this is the bevel part.
sizex 1.0600
sizey 1.0600

the button top is 0.78 and when entered into blender there is a HUGE gap. (once the arc is made)
in sketcup the gap is tiny (once the gap is made.)

i exported it as .3ds and the mesh in sketchup reads as 3" diameter

in sketchup i can make the button as 1.06", but once exported and imported into blender, the imported mesh reads as 1.0

anyway to correctly translate dimensions between the two? (i’m not knocking the way blender dimensions are done, i think it’s a simple way to measure.) is there maybe something i’m not understanding about the unit system?

my second question, why does blender calculate a circle outside a square of the same dimension?

blender. square and circle at location 0,0,0 both with a size of 1.0,1.0,1.0

sketchup.square and circle at location 0,0,0 both with a size of 1.0,1.0,1.0
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actually, you’ve got it wrong

the numeric input panel in object mode doesn’t show the SIZE of the object in units, it shows the scaling of the object [as a multiple]…

you’re going to have a really hard time doing anything precise in blender. … umm, just don’t… sketchup is at least as precise as you make it… blender is not at all.

Hello,

First, it sounds like you’re getting some digit rounding in there (1.06 rounded to 1.0). The easiest way to avoid that kind of problem is to make things really, really big. I’d try changing that diameter to 10.6 or 106 and then scaling down in the target app, be it SketchUp or Blender.

As far as being accurate goes, when I need accurate blender measurements I assume that one blender unit equals one meter and do the rest of the calculations manually. The real problem arises when you need finer divisions of the grid at low sizes, but again this can be resolved by making the model really big (10 blender units equal to one meter, for example). Under view properties, you can also set the grid spacing to 0.8 or 1.2; these might be more useful for you if you’re working in feet and inches.

When using the numerical entry box remember to use it on vertices / control points only. It’s basically the only way you’ll end up with decent accuracy, unless you’re attempting to scale or move an entire model.

Hope this helps.

as kattkieru says…use the numeric input in edit mode. The default size of a circle when added fresh actually has the radius of sqrt(2) (or 1.414). Go into edit mode, scale it down so that the radius is exactly .5, then back to object mode. the scale/size value in the input box still reads 1.00, right? Good. Leave that as your default “1 unit” circle, and copy it as needed, scaling to the desired size you want.

blender can be very precise (3 decimal places usually). You shouldn’t have any problems if you follow these rules.

I also make “measuring sticks” of various sizes for visual comparisons. (make a plane, delete all verts, ctrl click to make a vert and snap it to cursor (ideally 0,0), then extrude up (constrain in Z by exactly 1.0). Back to object mode (with size xyz still at 1). Now you have a meter stick (or mm or cm as you want) that you can scale likewise for other measurements).