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Eliolechat

Un esprit dans ma scène !?! Problème position objet

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Bien sur,  ça dépend de ses habitudes et de l'échelle des éléments sur lesquels on travaille etc, de notre coté ce sont des maisons, des bâtiments ; grands, moyens ou petits, presque toujours à placer dans un environnement rue, terrain, etc ...
Du coup c'est plus simple de bosser en cm ; une porte 90 cm de large, un garde-corps 100 cm de haut, un barreaudage 2 cm d'epaisseur, un jardin 800 cm X 450 cm, etc ... Je me vois pas faire des portes de 0,9 m et des barreaudages de 0,02 m.

 

 

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23 hours ago, zules said:

Archviz = architectural visualization : en archi on bosse en mètre

En archi peut-être, mais la visualisation architecturale, ce n'est pas de l'archi ;) 

Pour ma part, j'ai quasiment toujours mis le system unit a 10cm, et le display en fonction de ce que j'ai besoin sur le moment...

De toute façon , le but c'est d'avoir le system unit le plus médian possible par rapport à la scène actuelle, pour tout un tas de raison interne a max et aux renderers. C'est d'ailleurs l'une des premières raisons pour laquelle on fait les props dans des scène distinctes, pour avoir le system unit le plus adapté.

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1 hour ago, SugaR said:

pourquoi donc ? 

Quand tu as un objet de 10 cm de long tu dois donc le modeliser avec des cotes de 100 cm ? Ou je comprend pas ... cad que 1 cm reel  = 10 cm dans ton max ?

Je suis comme Nicolas, curieux d'en savoir plus :D 

 

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2 hours ago, patagoniak said:

Quand tu as un objet de 10 cm de long tu dois donc le modeliser avec des cotes de 100 cm ? Ou je comprend pas ... cad que 1 cm reel  = 10 cm dans ton max ?

Euh... Ok juste pour être sur, vous savez à quoi sert le system unit ? J'ai l'impression qu'il y a confusion entre le system unit et le display unit.

Peu importe le system unit, le display unit est uniquement là pour "aider" l'utilisateur. D'ailleurs plein de softs de 3d n'ont juste pas d'unités. Par contre le system unit est lui important (si on souhaite travailler à l'échelle, ce qui ne veux d'ailleurs pas dire grand chose dès qu'on commence à utiliser plusieurs softs avec échange de models...)

En gros, le system unit est la pour déterminer la taille d'une unité interne à max (donc ici rien à voir avec le display unit). Le system unit sert à pas mal de chose, par exemple, si vous avez eu des soucis de zoom (les steps sont très petites, ou inversement, ne permettant pas de zoomer correctement, c'est typiquement un problème de system unit (les steps du zoom étant lié au system unit). 

Pour reprendre l'exemple de Patagoniak, si je veux modéliser une box 10*10*10cm, avec un system unit à 10cm. Si je travaille sans unité dans le display unit, je ferais une box de 1*1*1. Si je travaille avec le cm en display unit, je ferais une box de 10*10*10cm (display), mais en interne (donc pour max, pas l'utilisateur), ca sera bien une box de 1*1*1. 

C'est ce que je disais plus tôt, le system unit doit être médian à votre scène. Vu que je n'ai quasiment jamais fait de scène dans max plus grosse que quelque dizaine de mètre, 10cm en system unit est franchement idéale car :

 - les objets les plus petit seront de l'ordre du millimetre, donc 0.01 system unit

 - les objets les plus grand eux font une dizaine de mètre, soit 100 system unit.

Résultat, mon system unit a 10cm est idéal, car médian. Si j'étais en 1cm (system), j'aurais du 0.1 / 1000, ce qui n'est pas idéal.

 

Par sur d'être bien clair, mais pour récapituler, peu importe ce que vous faites (archviz, vfx, industriel, animation, etc...), le display unit est juste la pour aider l'utilisateur et le system unit doit être le plus médian possible à la scène actuelle. Du coup peut importe vos préférences / habitudes, si vous voulez travailler en mètre, cm, ou mm (ou kilomètre xD), vous gérez ça uniquement sur le display unit.

 

 

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1 hour ago, SugaR said:

Euh... Ok juste pour être sur, vous savez à quoi sert le system unit ? J'ai l'impression qu'il y a confusion entre le system unit et le display unit.

 

LOL .. c'est bien possible, je met tjs tout pareil (disply et unit en cm), mais je vais lire ton explication avec attention, merci !

 

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Effectivement pas banal. Mais quels sont les avantages convaincants de privilégier un system unit médian ? Parce que si c'est juste les steps du zoom... Je me doute qu'il y a autre chose, mais je visualise pas.
Et c'est sans doute un coup de main à prendre, mais je trouve ça a priori plus pratique de faire correspondre system et display, je suis  bien trop feignant pour penser en unité  ? Quoique pourquoi pas, selon la nature du job.

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j'avais gardé ça de coté: 

 

Quote

There are a couple of things to keep in mind when dealing with units (especially System Units setup).

Precision!
Max always manipulates data internally in generic units, stored in single precision floating point format. This means that there are physical limits of how fine and how large the values can be.
If you are modeling the fine mechanics of a watch, you would probably go with 1 Generic Unit == 1 mm, which gives you lots of detail when dealing with sub-mm values. Obviously, the whole model would not be larger than couple of centimeters, so you are safe in both directions.
On the other hand, modeling an entire city would be an overkill at these same settings, as you never model with such precision all the crews in the construction of every window in every building. At the same time, if you are designing a sequence including detailed characters in that city, using 1 Generic Unit == 1 foot would be a disaster as you wouldn’t be able to get enough detail in your characters. For example, if you are using a spline to model a whip the character is holding, and want to use the NormalizeSpline modifier on top of it, you will discover that the lowest Generic Units value allowed by the modifier is 1.0, which does not let you apply it effectively to a whip modeled at 1GU=1 foot! Even worse, some plug-ins like SimCloth for example will be unable to solve the cloth collisions at such settings because of lack of decimal precision in the manipulated vertex data, boolean operations between small objects will always fail etc.
As if that is not bad enough, viewport navigation can become unusable when working at the wrong scale! Z clipping becomes difficult without using manual clipping planes. Rotating the mouse wheel one tick can zoom past your tiny character as the setup is made for a large city and not for bugs in the street…

So in a word, you have to consider the relative size of the objects and the minumum and maximum detail you are going to deal with.

There is an additional problem with loosing precision with increasing distance from the origin. As the position values grow, the ability of the application to represent values with floating point precision decreases. This is what the Accuracy field in the System Units setup is for. It lets you enter a distance to the origin and see what the finest possible detail would be.

Normally, when creating a model of the Earth (e.g. 1GU = 1000 km) , you can forget about representing its population at the same time. :slight_smile:

Data exchange.
When importing data, for example an architectural model or a model of a car made in AutoCAD or another external application, you want to end up with usable size.
Let’s say you have a 3D model of a house designed in AutoCAD using 1 Generic Unit as 1 cm, which is about 40 meters (4000 cm) wide.
And you have a detailed model of a VW Beetle also made in AutoCAD, but this time at the typical engineering scale of 1 Generic Unit = 1 mm. The length of the model would be 4080 mm, or 4.08 m (an old year 1970 1302 model). Obviously, the house is 10 times wider than the car, but both have about the same size in Generic Units - around 4000!

If you would import the two models into a 3ds max scene which is set to 1 Generic Unit = 1 cm, the house will transfer the data 1:1 from AutoCAD, giving you exactly the same Generic Units values in the max scene, but the car model would be imported 10 times larger!
If you would import the car model into a scene with 1 Generic Unit == 1 mm and then merge the saved scene with the house that was imported at 4000 Generic Units = 4000 cm, the model will land into the millimeters scene as 40000 units = 40000 mm = 4000 cm = 40 m, and the car will fit in the garage! (Same in the other direction).
So the knowledge of the System Units of both files helps 3dsmax scale the values when merging to give you objects that fit together despite the differences in the assumed meaning of the Generic Units used to store the data internally…

As you know, trying to mass-rescale the units after the fact can lead to problems, but for mergin single ASSETS into a scene the system really works. It is a good idea to think about the units before creating a single polygon, as it could make the difference between creative heaven and fighting-the-scene hell!

User Interface and Workflow
The “Display Units” settings are just an UI layer that converts the internal Generic Units representation into something a human can understand better. They are NOT used to match data between files and don’t affect the way the data is stored, but can affect the way the data is entered. For example, if in the above example you were interested in putting a small block together made of instances of the house and your system units were still set to 1GU==1mm, you would have to enter large numbers with lots of zeros just to move the house a steet away. Changing the UI to display Metric> Meters will show you a house that is 40 m wide, and to move it 60 meters to the side you would have to enter only 60 in the Transform Type-In, not 6000 !
Also, these settings can be a life saviour when dealing with international projects where the two sides use different systems (SI metric vs. Imperial). Let’s say a model for a movie set was developed in Canada using meters and shipped to a company in Hollywood using feet and inches. The guys there want to do some work on the model but have no idea what the values mean in the real-world measurements they are used to.
Simply changing the Display Units to show Feet and Decimal Inches will turn a 40 meters house into a 131’2.803" house without touching any data internally. The guys can manipulate the model and UNDERSTAND how big it really is without learning the metric system - max does the math for them!

I hope this helps a bit. I am sure I have just scratched the surface.

Bobo

 

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