wildparky Posted August 28, 2003 Share Posted August 28, 2003 how can i get a velocity of splitted particle (when it's birth) ? not runtime velocity but creation velocity Quote Link to comment Share on other sites More sharing options...
wildparky Posted August 28, 2003 Author Share Posted August 28, 2003 like a creation expresion of maya particle ! Quote Link to comment Share on other sites More sharing options...
FrankFirsching Posted August 28, 2003 Share Posted August 28, 2003 In the Attributes-tab of your split-POP you only need to set the drop-down-box to "set initial velocity"? You then have to set the Variance to zero and enter your expression in the Velocity fields. Quote Link to comment Share on other sites More sharing options...
wildparky Posted August 28, 2003 Author Share Posted August 28, 2003 my splitted particle velocity is change per frame. i want to a constant velocity of just birthed Quote Link to comment Share on other sites More sharing options...
anakin78z Posted August 28, 2003 Share Posted August 28, 2003 err... well, the velocities get affected by what you have going on in the rest of your particle system. If you don't want the velocities to change, don't apply any drag, force or anything after the split. Quote Link to comment Share on other sites More sharing options...
wildparky Posted August 29, 2003 Author Share Posted August 29, 2003 maya particle expression is divided two type, one is a creation expression, the other is a runtime expression. i think that commonly '$VX,$VY,$VZ' is a runtime variable in houdini . my splited particle's color is chaged by a changed velocity each frame . ----> $CR=dot(vector3($VX,$VY,$VZ), vector3(2,2,0)) i want someting like this ----> $CR=dot( a rest velocity(when it is birth), vector3(2,2,0)) then, $CR can have a constant value all the time . isn't it possible by expression? Quote Link to comment Share on other sites More sharing options...
AndrewVK Posted August 29, 2003 Share Posted August 29, 2003 Add Group POP: Group Name: InitVelGrp Rule (enable): $AGE == 0 -------------------------------------------- Add Attribute POP: Source Group: InitVelGrp Name: initvel Type: vector Value: $VX $VY $VZ -------------------------------------------- Add Drag POP, open geometry spreadsheet, run simulation and compare "V" and "initvel" attributes. Quote Link to comment Share on other sites More sharing options...
wildparky Posted August 29, 2003 Author Share Posted August 29, 2003 hi! andrewVK, thanks your advise it's works. Quote Link to comment Share on other sites More sharing options...
chrisedu Posted May 18, 2007 Share Posted May 18, 2007 I am trying a similar setup to use an attribute POP to create a variable to scale a geometry copied on a copy SOP. at POP network: group POP : $AGE==0 attribute POP source group = group name = yscale value = rand($ID ) on Details View, it shows me the yscale value correctly but I can't use this attribute at copy SOP. thx for any help cheers Quote Link to comment Share on other sites More sharing options...
old school Posted May 18, 2007 Share Posted May 18, 2007 This is best done with the float pscale attribute. The Copy SOP will use this to scale your copies if present on your right hand template input points. You can add pscale with a Point SOP or in POPs use the Property POP's Misc folder. Quote Link to comment Share on other sites More sharing options...
chrisedu Posted May 18, 2007 Share Posted May 18, 2007 Hello Old School! thx, it worked perfectly! just wondering why I can't use an attribute pop to pass information to copy sop instead? kind regards Quote Link to comment Share on other sites More sharing options...
antoinedurr Posted May 18, 2007 Share Posted May 18, 2007 Add Group POP:Group Name: InitVelGrp Rule (enable): $AGE == 0 -------------------------------------------- Add Attribute POP: Source Group: InitVelGrp Name: initvel Type: vector Value: $VX $VY $VZ -------------------------------------------- Add Drag POP, open geometry spreadsheet, run simulation and compare "V" and "initvel" attributes. Even simpler, just add a name into the 'birth group' field of the split POP (or source POP), leaving 'preserve group' unchecked. I have 'bgroup' (for birth-group) in by default on all my source POPs, as that lets me easily tweak values at birth time. Quote Link to comment Share on other sites More sharing options...
old school Posted May 19, 2007 Share Posted May 19, 2007 just wondering why I can't use an attribute pop to pass information to copy sop instead? This is one part of the Copy SOP that is quite black box. Because the Copy SOP has to deal with the template attributes internally, it is difficult to support custom local variables. You can use the point() expression to index in to the the right input template geometry but that get's slow. Many times I just transfer the attributes from the template to the copied geometry then use a whole host of SOPs that use those transferred attributes to do stuff. Faster than using point() expressions. leaving 'preserve group' unchecked. I never make persistent groups from any source, location or split POPs. I leave that for a subsequent Group POP using the group from "source" option. Birth groups are great for initialzing stuff before the particles hit the first time step. I have 'bgroup' (for birth-group) in by default on all my source POPs, as that lets me easily tweak values at birth time. I usually use random group names like "just_born" "just_split". 'bgroup' is as good as any and is shorter. Good enough for me! Quote Link to comment Share on other sites More sharing options...
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