willlinks Posted April 23, 2009 Share Posted April 23, 2009 Hi everyone, I was trying to make small objects move on the surface of a large object. However, the small objects start rotating itself along X axi when I used points of the surface to copy and animated. I want to make them keep facing forward (towards the direction they are proceeding). I tried to use up vector but I couldn't make it work.... Please help me Thanks in advance. Quote Link to comment Share on other sites More sharing options...
pclaes Posted April 24, 2009 Share Posted April 24, 2009 (edited) I used the edge force in the point sop as the up vector. Because the up attribute is a vector it should be changed alongside with the normals as it goes through the transform operations. Basically you copies are now oriented towards their closest neighbours (this is based upon the point order that influences the way the edge force is calculated. The result is a vector formed by $PT - ($PT+1) ), do a search on edge_force here on odforce to understand some of the variable/attribute declaration better. I don't know if this fully solves your problem? - oops just read you wanted to keep them facing forwards, let's see if I can adjust the file a bit to do that. facingDirection_02.hipnc Edited April 24, 2009 by pclaes Quote Link to comment Share on other sites More sharing options...
pclaes Posted April 24, 2009 Share Posted April 24, 2009 This one should do it, a cross product between the z-axis (this should be the axis you are rotating around, you really want to define this somewhere in a control variable a bit higher up on the network in case you want to rotate around a different axis) and the surface normal. check the visualization null to see the what the up vector looks like. facingDirection_03.hipnc Quote Link to comment Share on other sites More sharing options...
willlinks Posted April 24, 2009 Author Share Posted April 24, 2009 This one should do it,a cross product between the z-axis (this should be the axis you are rotating around, you really want to define this somewhere in a control variable a bit higher up on the network in case you want to rotate around a different axis) and the surface normal. check the visualization null to see the what the up vector looks like. Yeah, This is exactly what I wanted to do! I've never used cross product before. It is so useful Thank you so much, Peter! Quote Link to comment Share on other sites More sharing options...
pclaes Posted April 24, 2009 Share Posted April 24, 2009 Yeah, This is exactly what I wanted to do!I've never used cross product before. It is so useful Thank you so much, Peter! It really is, dot product as well. Not that I want to shamelessly advertise or anything, but I created some video tutorials a while back which explain some of this stuff in Houdini terms. First covers a bit of the math, then convert it into Houdini expressions. So yeah, if you're curious have a look: http://www.3dbuzz.com/xcart/product.php?productid=58 It's about effects, but really it's about data manipulation in sops, pops, vops and using expressions. Quote Link to comment Share on other sites More sharing options...
willlinks Posted April 24, 2009 Author Share Posted April 24, 2009 It really is, dot product as well. Not that I want to shamelessly advertise or anything, but I created some video tutorials a while back which explain some of this stuff in Houdini terms. First covers a bit of the math, then convert it into Houdini expressions. So yeah, if you're curious have a look: http://www.3dbuzz.com/xcart/product.php?productid=58 It's about effects, but really it's about data manipulation in sops, pops, vops and using expressions. Oh, cool! I'll check it out. I was driven by necessity to use expressions recently. Thanks again. Quote Link to comment Share on other sites More sharing options...
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