glassman3d Posted October 11, 2010 Share Posted October 11, 2010 Hi all I am using the pyro tools to generate clouds. I am having a problem with the initial state on the low res pyro object. I am looking to sim from an initialstate without emiting anymore density into the sim. Ultimatlty i aim to get a whispy cloudiness similar to sirrus clouds I have cached out a pyro sim to get the initial state that i wanted. I have brought this into a geo node, then I have used VOPs to add a vignette to the density field (purely for asthetic reasons) and then delete sops to seperate each relevant volume primitive or primitives to plug into the relevant initial data slots on the pyro node in DOPS ie density, fuel, temp, and vel. as soon as i sim, the density falls by 90% between frames 1 and 2 then the density holds at that level throughout the sim. I have even tried scaling up the density by a factor of ten to make up for this loss but the density loss becomes greater. I'm not using combustion in my sim and diffusion is set very low. I am also using the BFECC advection type as i have heard that this is better for holding density. is there a fundamental step i have missed in my setup somewhere? It would be fantastic if i could prevent or limit this initial density loss - it only happens on the first frame then levels out. Has anyone had any similar problems? please see attached hipfile for details thanks in advance densityLoss_odForce.hip Quote Link to comment Share on other sites More sharing options...
~nature~ Posted October 12, 2010 Share Posted October 12, 2010 Hi,glassman3d, This problem should suffer from the operation between the density field and sink field inside the pyro solver which actually confine the density field range to be less than or equal to one. so no matter how large it was, it will be modified at the initial stage of pyro solve that is when you jump from frame 1 to frame 2. So I guess sidefx add scale option to the intial density data of smoke is a weak point to pyro solver. Hope it helps Cheers Quote Link to comment Share on other sites More sharing options...
glassman3d Posted October 12, 2010 Author Share Posted October 12, 2010 (edited) Hi,glassman3d, This problem should suffer from the operation between the density field and sink field inside the pyro solver which actually confine the density field range to be less than or equal to one. so no matter how large it was, it will be modified at the initial stage of pyro solve that is when you jump from frame 1 to frame 2. So I guess sidefx add scale option to the intial density data of smoke is a weak point to pyro solver. Hope it helps Cheers Hi ~nature~ thanks! that has saved me days of testing! It does definately seem a bit strange that you can scale density to values over 1 that then get overridden instantly by the sink mask Maybe a better scale operation on the pyro density data field would raise the average values yet keep them clamped at 1. any ideas anyone how to acheive this?? I'm gonna have a look now cheers Edited October 12, 2010 by glassman3d Quote Link to comment Share on other sites More sharing options...
bunker Posted October 12, 2010 Share Posted October 12, 2010 you can update the apply sink stage with a simple gasfield vop. density = clamp(density-sink,0,1000) > just to make sure the density values are positive densityLoss_odForce_2.hip or disable the sink if you don't need it... Hi ~nature~ thanks! that has saved me days of testing! It does definately seem a bit strange that you can scale density to values over 1 that then get overridden instantly by the sink mask Maybe a better scale operation on the pyro density data field would raise the average values yet keep them clamped at 1. any ideas anyone how to acheive this?? I'm gonna have a look now cheers Quote Link to comment Share on other sites More sharing options...
~nature~ Posted October 12, 2010 Share Posted October 12, 2010 (edited) Again,the houdini11 new "source apply" HDA suffers the same problem, the "emission amount" parameter takes no effect when the value is greater than 1, because the source field can never be greater than 1 in pyro solver, but the density field can be scaled up above 1, the "smoke amount" parameter is the multiplier of source field before it is added to the density field. Hope sidefx can look into it. Edited October 12, 2010 by ~nature~ Quote Link to comment Share on other sites More sharing options...
glassman3d Posted October 19, 2010 Author Share Posted October 19, 2010 hi bunker any chance you could reload that example file? It keeps crashing my houdini when i try to open it??? Quote Link to comment Share on other sites More sharing options...
bunker Posted July 27, 2011 Share Posted July 27, 2011 The file works fine. You need Houdini 11. hi bunker any chance you could reload that example file? It keeps crashing my houdini when i try to open it??? Quote Link to comment Share on other sites More sharing options...
ikarus Posted July 27, 2011 Share Posted July 27, 2011 why not just scale your density down to 0-1 then increase the density in the visualization settings Quote Link to comment Share on other sites More sharing options...
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