Author Topic: CMs or MMs for Arch Viz scene units in MAX?  (Read 251 times)

2019-04-16, 15:04:55

Rhodesy

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We currently use MM for our scene units in Max, largely as a crossover from traditional CAD drafting and architectural conventions in the metric world. But Maxes default is CM and every asset we buy seems to come as cm. We also sometimes get issues with drawings off the working plane - which perhaps we would get less of if we used CM? Also even in a medium sized scheme I get massive Z-fighting in my perspective view and I wonder if this is just because of the way Max handles small units in a bigger scene?

Anyway it would be interesting to hear what others have their units set to as I'm thinking maybe we should switch if people are getting less problems sticking with CMs.

Thanks

2019-04-16, 15:28:05
Reply #1

dzintas

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I would recommend using centimeters or even meters for bigger projects. For me, mostly working with interiors centimeters works great.
Millimeters only useful from small scale models.


2019-04-16, 15:38:21
Reply #2

pokoy

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Somewhat of a rule of thumb - for any system unit you choose, the accuracy is sufficient approximately for 3 decimals and lower 4 digits.
Your mileage may vary, but the result will be like this:

for mm - 0.001 mm and 1000 mm will be ok - 0.0001 mm and 10 000 mm will be problematic
for cm - 0.001 cm and 1000 cm will be ok - 0.0001 cm and 10 000 cm will be problematic
for m - 0.001 m and 1000 m will be ok - 0.0001 m and 10 000 m will be problematic
etc...
For the small values, you'll have rounding errors sometimes, for large values you'll see that, for example, object placement will 'jitter', you won't be able to place objects precisely anymore, they'll 'jump' to the next rounded value.

We use meters for system units which allows us to model with sufficient detail in the mm range and allows us to move objects 100s of meters without problems.
Choose system units depending on what your scene will show (small scale or large scale) and how precisely you need to model or place something.

Just in case - we're not talking about display units (these are independent from system units) but system units, right? Some people are mistaking one for another so it's important to know what's what.

2019-04-16, 16:54:34
Reply #3

PROH

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Hi. I agree with pokoy. Just a little note: if you work with meters as system unit, you need to set Max to use 4 digits (.0000). Otherwise even your mm (3rd decimal) won't be precise.

I mostly work in meters or cm, and occasionally I model parts in cm and then import/merge them into the "meter-model". If you check the "respect system unit" checkbox in the system unit dialog box, the scaling will be done automatically during import/merge.

Hope it helps

2019-04-16, 17:04:10
Reply #4

Rhodesy

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Thanks guys, yes I was referring to system units.

Interesting. Well I might suggest we have a go at at least upping to CMs and give it a try going forward. I can see metres getting a bit frustrating, with a lot of 0.01 sort of measurements going in for me but CMs shouldnt need as many decimal points.

2019-04-17, 08:35:39
Reply #5

dzintas

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Thanks guys, yes I was referring to system units.

Interesting. Well I might suggest we have a go at at least upping to CMs and give it a try going forward. I can see metres getting a bit frustrating, with a lot of 0.01 sort of measurements going in for me but CMs shouldnt need as many decimal points.

There is few ways to deal with that. You can always stick to mm in display units. That way you wont need to type everything with decimals, other way is to just specify units at the end of the measurement. If you're using meters for example and typing 2500mm for a box height you will get end result of a 2.5meters. I mostly use this to convert imperial measurements to metric.   

2019-04-17, 10:09:29
Reply #6

Rhodesy

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Thanks Dzintas. Yes I like the way we can have different display unit. Good that we can stick with mm there for habit.

For those that jump between M and CM do you run in to issues with real world texture sizes not scaling right with merged assets? CMs look to be working well in my initial tests but we are working on a masterplanning model that is a few city blocks and Metres visually help with the Z fighting no end!

2019-04-17, 12:00:59
Reply #7

PROH

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Hi. In general things behave correct when merging cm models into files using meter, but occasionally I've seen problems with the UVW scaling. Haven't yet found any system in "when" or "why" this happens, but usually it's simple to fix.

Just remember to check the "respect system units" in the system unit dialog box!

Hope it helps

2019-04-17, 12:09:21
Reply #8

romullus

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AFAIK, 3ds max procedural maps has problems when converting system units. Parameters like noise, cell size, are bound to system units, but they completely ignorant of... well, "units". So, if noise size was set 1 (cm) in a scene, then converting it to meters, noise size will still be 1 (m).
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2019-04-17, 12:26:11
Reply #9

PROH

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Yes. Some parameters will not change correctly. The way some procedural maps are handled, is that the tile value changes instead of the size value. So if a cm procedural with tile value 1 is merged into a meter file, then tile is changed to 100. IIRC this is limited to 3 digits, and therefore you might get problems when merging mm files into meter.

My comment above was regarding the real world UVW, but there are specific values that doesn't change correct, like "round edges". When correcting these values, it's worth noting, that all you need to do is tapping in the original unit-name, and Max will convert the value itself. F.x.: If your original value was set set to 1mm and comes in as 1m, then replace "m" with "mm" and the value is automatically changed to 0,001m.

Hope it helps

2019-04-17, 16:51:59
Reply #10

Rhodesy

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Thanks for the info. I think it is likely that we will stick to CMs and just live with some issues in any extra large scenes which arent as common.