Units and Sizing

Units and Sizing

Okay, this is stupid, and I know it's stupid, but searching the forum isn't giving any answers, and the problem appears throughout Cheetah 3D.

Has anyone got a definitive answer about setting units and sizes when working with Cheetah 3D?

Apparently it's a unitless system, except that dynamics DOES use units for calculations and defaults to 1 unit = 1 meter. But how do you set the Grid Size? What about Quantize, or Grid Snap values? When you call up the Ruler - what units does it use? Can you change that? How does a choice of units affect Clipping distance? Because it obviously does. And what about Optimizing a mesh? Because what size you're working in affects the ability to weld close vertices without collapsing in odd places. Knowing all this, how do you set up a blue print to work at correct scale?

Basically has anybody summarized how you set up an accurate scale or size for working in Cheetah 3D and set all the relevant parameters to work together?

Thanks.

Hi Kurt,
you don't need to set up anything because the units of all the tools are the same.
0.01 Ruler distance is the same as 0.01 clipping distance or optimize distance or transform distance.

Only when you start a project you need to define for yourself what the scale should be.

Modeling a warrior of 2m height would be reasonable with one Cheetah unit = 1m.
Then all the measures of all tools would work in meters, because you have determined so, no need to tell the app about it :smile:

Making a gemstone ring would work better with one unit = 1 cm = 0.01 m.
Then all tools measure in centimeters.

You have to decide how to interpret the units once and then stick to it, there will be no problem because all the tools work in only one and the same coordinate system.

Problems may arise with scaled objects, those have a different local coordinate system than the global one.
Therefore you better not model with scaled objects or use burn scale tool.

When you import objects that have to be scaled to fit into the scene you have to live with the complications but what you create yourself will be consistent with everything else as long as it is scaled 1/1/1.

As you said, dynamics are preferrably used with one unit = 1m, but for everything else you are free to determine what one unit shoud mean.

An exception are certain texture nodes like checkerboard or dots, they have indeed a different scale which is very confusing but can be dealt with by multiplying with a correction factor if needed.

misoversaturated said:

Hi Kurt,
you don't need to set up anything because the units of all the tools are the same.
0.01 Ruler distance is the same as 0.01 clipping distance or optimize distance or transform distance.

Only when you start a project you need to define for yourself what the scale should be.

Modeling a warrior of 2m height would be reasonable with one Cheetah unit = 1m.
Then all the measures of all tools would work in meters, because you have determined so, no need to tell the app about it :smile:

Making a gemstone ring would work better with one unit = 1 cm = 0.01 m.
Then all tools measure in centimeters.

You have to decide how to interpret the units once and then stick to it, there will be no problem because all the tools work in only one and the same coordinate system.

Problems may arise with scaled objects, those have a different local coordinate system than the global one.
Therefore you better not model with scaled objects or use burn scale tool.

When you import objects that have to be scaled to fit into the scene you have to live with the complications but what you create yourself will be consistent with everything else as long as it is scaled 1/1/1.

As you said, dynamics are preferrably used with one unit = 1m, but for everything else you are free to determine what one unit shoud mean.

An exception are certain texture nodes like checkerboard or dots, they have indeed a different scale which is very confusing but can be dealt with by multiplying with a correction factor if needed.

Click to expand...

Good explanation. I agree 100%. You decide what 1 unit is (requires some experience and thought), and stick with it. Changing mid-project is awkward.
—shift studio.

* If useful, check the subsequent option for non-decimal metrication:
* For a past project I needed a 30x30 (= 1 foot, ±) grid / minor plus a 90x90 grid (= 1yard, ±) / major. I decided to superimpose the major grid on C3D´s standard grid, ie 1 yard = 1 standard step.
* To generate some simple visual guides, I produced a couple of planar grids for the XZ horizontal plane and the XY elevation plane at the 1 foot grid spacings.
* For WIP, toggling off the visibility of the standard grid is useful (I have defined a hotkey for that), as zooming the camera will display the original decimal grid-lines, updated to a suitable resolution, which just is confusing.
* In the transform tool, I set the snap to a practical value, eg 0.3333 or 0.1667 (this clearly depends on the "customised" grid).
* If you require US “metrics”, you can also deploy the option to use basic math operators (+,-,*,/) in numeric fields for parameters and tools. Simple example: You have decided on a grid 1 foot square. To operate with inches simply add “/12” to the numeric input; if yards are required, add “*3”; for lightyears, you need to multiply with 3,104e+16 :frown: :tongue:
* Just bear in mind that in some cases you will introduce rounding errors. Also consider that the ruler will use the C3D standard grid for distances.
* I almost always ignore the size parameters. Some reasonable time is mandatory in any case to plan a (series of) model(s) before sitting down in front of the Mac to implement preexisting mental concepts. Your work-flow may differ.
* As Shifty and Miss OS have implied, this is primarily a matter of experience and pre-production logistix.

Thanks for all the useful information everyone. As usual it will take some time for everything to sink in.

I ran into trouble when trying to Optimize a mesh. I then ran a bevel operation, which failed. Turns out some nearby points had NOT merged during the Optimize, and the bevel tool could not do it's job.

I finally scaled my mesh up quite a bit, then burned the transform, and was able to get it to optimize. After that it beveled without any problems, but I did question whether or not I had made an error in starting to model without considering the size and scale.

Oh well, lesson learned, on to other modeling tasks.

Thanks again.