# RBD: how to set the scene size for simulation correctly?

THREAD CLOSED
 Thread Tools Display Modes
 11 November 2011 ScratchARTS Veteran   portfolio Philipp Kratzer 3D-Artist Montfort Advertising Bregenz, Austria RBD: how to set the scene size for simulation correctly? Hey there CG-talkers! I'm exploring Houdini at the moment, been through some of the basics and right now I'm messing around with RBD (going through a Digital Tutors Tutorial "Fundamentals of Rigid Body Dynamics in Houdini"). While doing so, I'm wondering how to correctly set the scale for my scene and objects in order to get a physically correct simulation result? I found HIP File Options within the Preferences saying 1m = 1 Unit, 1kg = 1 Unit. So far so good. But scaling for example an Apple (model provided by Digital Tutors) and a Groundplane to 0.1=10cm units (SOP-Level using a Transform Node) gives me very odd results. The apple is falling unrealistically fast. For the math part, it makes somehow sense, because Gravity is set to -9,8m/s^2) but it doesnt look real...I'm no physicist by all means, but it looks strange. The false scale values (the apple being about 2 units in size which would be 1m radius(!!) looks natural though. I'm confused So how do you approach this scale issue correctly? Thx in advance for your help, and again cheers!! __________________ www.scratch-arts.net share quote
 11 November 2011 rjw Veteran Definitely change the main preferences units to what you want. It defaults to 1 Houdini unit equalling to 1 metre. This preference only works before you build your simulation. It will adjust any Gravity Forces and Density/Mass parameters on new Simulation objects. Changing the above preference does not adjust any of the parameters in the simulation which is what I presume you are doing. You have to go in to your simulation object nodes (RBD Object DOP, RBD Glue Object DOP, etc) and adjust the density parameter. Just multiply it by your scale factor. Same goes for gravity. Actually, here's a tip. You can create a global variable in Houdini and call it say "UNIT_SCALE". You can set this in the "Aliases and Variables..." Dialog from the main Edit menu. You can then multiply your Density values and Gravity (and anywhere else you need to adjust the scale for) and just change the global variable and done. Density: 1000 * \$UNIT_SCALE Hope this gets you going. -jeff share quote
 11 November 2011 penboack Penboack portfolio Charles Kirk United Kingdom You need to think about the physics. If you think about what dropping an apple looks like, over a range of 50-100cm, say from desk height to the floor, it happens very fast, so you need to setup the simulation in such a way that the units give you the result you are looking for. Drop an apple from a couple of floors up, how long would it take to reach the ground and what would it look like? share quote
 11 November 2011 ScratchARTS Veteran   portfolio Philipp Kratzer 3D-Artist Montfort Advertising Bregenz, Austria Hey again! Thx for the tips folks! It seems to work now! I just tried out everything you said. The global variable ist great, one location to set the value, and then simply use the variable. Nice one! That's indeed helpfull (also for other things, not just RBD's). I also took penboack's tip seriouse and searched my attic for my good old physics teaching books and did some math right away. According to the book (and a friend of mine wich actually is physicist) it takes an apple about 0,4something seconds (10 frames), to fall from 30cm to hit the ground plane. So it was perfectly correct what I saw at the first time. What made it look odd I guess was that I had to less substeps calculated for my simulation to make the apple perform correctly. I raised the number up and it looked nice! And I guess I had become so used to look at too slow running simulations (which is default in Houdini due to the large values for one unit being 1m) that I interpreted the correct solution being "to fast". Thx to both of you for helping me out with this one! __________________ www.scratch-arts.net share quote
 11 November 2011 CGTalk Moderation Expert Thread automatically closed This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum. __________________ CGTalk Policy/Legalities Note that as CGTalk Members, you agree to the terms and conditions of using this website. share quote
 Thread Closed share thread

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off CGSociety Society of Digital Artists www.cgsociety.org Powered by vBulletinCopyright ©2000 - 2006, Jelsoft Enterprises Ltd.
Minimize Ads
Forum Jump
 Please select one User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home -------------------- Gallery     Latest Entries     Featured 2D     Featured 3D     CG Awards     Community Awards Main     News     General Discussion     Off Topic     Recruitment         Temp Job Board Challenges     CGS Environment 101     Education     Demo Reel     Portfolio Review GROUPS WIP ADVICE     CGS Pro     New 2D/3D Sketchbooks 2018     WIP 2D/3D & Animation         WIP/Critique: 3D         WIP/Critique: 2D             Speedpaints & Sketchbooks         WIP/Critique: Animation     Partners and Groups         Art Direction and Interviews         Kitbash 3D Thunderdome         Collaborative Projects Autodesk     Autodesk Maya         Maya Dynamics         Maya Rendering         Maya Character Setup         Maya Programming     Autodesk Miscellaneous         Autodesk MotionBuilder         Autodesk Mudbox         Autodesk Softimage             XSI: Programming             ICE: Interactive Creative Environment     Autodesk 3ds max         3dsMax Tutorials & Tips         3dsMax Resources         3dsMax SDK and MaxScript         Plugins & Add-ons         Particle Flow     Mudbox Featured Gallery ZBrush     Featured Zbrush Gallery     Pixologic ZBrush     Keyshot     Marvelous Designer Texturing     Allegorithmic Substance         Substance Designer         Substance Painter         Substance Featured Gallery     Texturing XYZ     Mari     Marmoset Toolbag Software     Maxon Cinema 4D         Cinema 4D Resources     Side Effects Houdini     Compositing Software         The Foundry Nuke         Adobe After Effects         Autodesk Effects and Compositing         Eyeon Software Digital Fusion     Additional Software         Lightwave 3D             LW Resources             LW Tutorials         The Foundry Modo             The Foundry Time Travel Challenge         E-on Software Vue         Photoshop / Painter         Blender         3DCoat Techniques     Art Techniques and Theories     Digital Matte Painting         Digital Matte Painting Mini-Challenge     Modeling         Modeling Challenge             Member Model Collection     Texturing and Surfacing     Character Rigging     Animation     Lighting and Shaders         Lighting Challenges     Compositing and Editing     Anatomy and Figurative Art         SPOTLIGHT: Best of the Artistic Anatomy and Figurative Art Forum         Tutorials and Workshops         Personal Anatomy & Sketchbook Threads         References, Resources, and Supplies Technical     VR/AR     Master Virtual Reality with BrioVR     Workstation Builds     Game Engine     Graphics Programming     Technical and Hardware     Support and Reported Post
Miscellaneous

All times are GMT. The time now is 04:07 AM.

Powered by vBulletin
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.