Hi, relative newby (2 years), having issues with an animation.

The scene is Outer Space, Earth in front and the Moon flies by in front of the camera.  The problem is, the Moon is set to follow a path (circle) smoothly but for some reason it is only moving every 3 or 4 frames, so it is stuttering past rather than floating smoothly by.

Having looked at the % along path, that is changing at every frame so it appears that the position is being rounded up or down

Units are KM, system Units are M. As it’s got stereo cameras I need the KM scale, I’m wondering if it can’t cope with the distance (Earth is at 0,0,0, Moon is at 0,33000,0, circle radius = 38300 KM), but I don’t feel it should with these units.  I also have a Satellite in the scene, it follows a smaller circle and moves smoothly, but it’s position is only 4300KM from zero and its circle radius is 3.2KM.

Any Space nerds out there might notice the measurements are a little off - I’ve had to use some artistic licence to get the Satellite (small object) to work with the Earth (humungous object).

I’m yet to master this program so it may be obvious, but I’d love if someone can help me out here.  I was supposed to have a 3 week deadline but due to other jobs coming in that’s now just 3 days and the other Max guy here is off sick.  Not that I’m panicking at all, y’know!

Kelly

3DS Max 2011 / Showcase 2011 (Backburner 2008.1.1)
Mac Pro (running Windows 7) all 64 bit
Intel Xeon E5520 @ 2.27GHz 2.39GHz (Dual) 16GB Ram
NVidia GeForce 9500 GT x2 + GeForce GTX 285

Highly likely rounding - Max only uses single precision floating point maths which is prone to rounding errors with very large or very small values.

Consider a single straight line exactly 100 units long and an object following that path for exactly 100 frames. Each frame will record the position at each 1/100th of the length of the line i.e. it will move 1 unit per frame. Now double the length of the line. Each 1/100th will be double the distance (2 units).
Now extrapolate that to your situation where your system units are Metres, path radius is 38,000 KM (displayed dimension) but is in reality 38,000,000 (1000M per KM) - a value already way outside the capabilities of single precision numbers. The length of that path will be 2*PI*R which is 238,761,041 - I’m not surprised you’re having problems.

The only way to overcome the problem is to use system units of such a size that the values required are orders of magnitude smaller. Then, of course, you will run into the opposite problem - some of your dimensions (moon diameter for example) will become absolutely tiny. More than 2 decimal places in a dimension will cause rounding errors and considering the values involved that will be quite likely to happen.

The trick is to choose system units in such a way that the large values aren’t too large and the small ones aren’t too small - even if doing so uses non-standard values for the system units. For example, where Metres are too large (smaller simensions have too many decimal places) and cm are too small (large dimensions are too large) then I would use system units of “1 unit = 10cm” (aka a decimetre) which is non-standard in the sense that it is not a provided unit, but it removes a “0” from the large numbers and a decimal place from the small ones thus bringing everthing within the range which Max can comfortably handle.

Another trick is to split the path into multiple smaller paths. Because the Path Constraint works on percentages, you will get better resolution per path than with the original circle - 4 times better if you split the circle into 4. Apply Path Constraints to Dummy objects (1 per path) and a Link Constraint from the moon to each dummy in turn. Watch the curves though as you will want them all to be linear (no speed-ups and slow-downs).

Max 4.2 through 2013.
XP-64 (SP2)
NVidia 9800GTX-512 (Driver 266.58).
Core 2 Quad Q6600 2.4GHz, 8Gb Ram, DX9.0c.

Hi Steve,

Worked a charm, thanks so much!  I just removed the circular path for the Moon and replaced it with a (relatively) short line, now it floats smoothly!

I don’t have time at the moment to work out the maths in your post, but I will definitely revisit this for the next time, really useful stuff, especially about the in-between Unit scales of 10cm (or 10/100m in my case).

Thanks so much!!

Kelly

3DS Max 2011 / Showcase 2011 (Backburner 2008.1.1)
Mac Pro (running Windows 7) all 64 bit
Intel Xeon E5520 @ 2.27GHz 2.39GHz (Dual) 16GB Ram
NVidia GeForce 9500 GT x2 + GeForce GTX 285

Some info on that issue here.

Why not give 3ds Max the same precision as Autocad!

They’ve had years and still not up to snuff on accuracy in Max, yet!!!!

Samab 13 June 2011 06:58 AM

Some info on that issue here.