Mis-match Of Attributes

[JohnnyBGoode]

hey all,

sorry for the basic question, but its something that i want to understand better - and want to know if there is any way i can stop it warning.

basically, i have a merge sop that is giving me the yellow warning of

'a mis-match of attributes on the inputs was detected'...and i want to know how to stop this and define attributes myself

i am assuming this has something to do with the shading/uv's.

in simple terms i have a sphere with slapped on shader. This sphere is copied and the new one given a uv'd texture and the they are merged together

as one has uv attribute defined, i am assuming that when it merges the other creates uv's but all set to 0? so i expect that i have to explicitly define the attributes before merging them?

If i want to export as obj later, and the two sphere's have same uv space i assume this will be a problem - how do i make sure they dont....

sorry for the elementary question, its just something i want to clear up before exporting obj's or making otl's

cheers

J

[deecue]

hey johnny,

looks like you've pretty much figured it out yourself but to clarify:

as one has uv attribute defined, i am assuming that when it merges the other creates uv's but all set to 0?

yes, this is true and you can confirm it by checking out the spreadsheet on the merge sop.. what's happening is as of the merge, houdini sees this as one object/surface.. so now, instead of two individual pieces of geometry with say 42 points on them each, you now have one with 84. but wait, the 42 points on that piece have this attribute called UV.. now, that my geometry is 84 points, i can't just have an attrib on some points and not others.. so it warns you (with a yellow flag, not red) that this has happened.. and in order to fix it, houdini has created the attribute for the other 42 points and just set them to 0. this is exactly what would happen if you used an attribcreate sop and used a specific group number.. it's not just going to create the attribs for just that group.. it's going to create it for every point/vert/prim and just apply the value you set to the ones in the group while applying 0 to the others. so essentially, there is nothing wrong or broken here, it's just houdini warning you of what has happened and that it did something to correct it.

....and want to know if there is any way i can stop it warning.....and i want to know how to stop this and define attributes myself....how do i make sure they dont....

there's a number of ways to do this.. for your specific example, you could just create the uv's on the original sphere before copying it and merging it back together. that way the copy will include the attrib and won't have an issue when merging back together. another method is the attribcopy sop. that will just copy the attrib and values, point for point from one geometry to the other..(if the destination geo is larger in numbers, the attrib is cycled).. yet another method is the attrib transfer sop.. this will attempt to create attrib's on the destination geo based on distance functions.. very handy indeed.. and of course there is always the attrib create sop to define custom attribs and variable mappings. as well as the attribute sop which allows renaming and deleting of attribs.. i would suggest going and trying them all out.. just type in tab->attrib and you'll get a whole list of things to play with..

hth,

dave

[Visual Cortex Lab]

deepcue ... THANKS.

this clarified to me this warning as well.. i was on the right way to it.. but your explaination has been THE clarification

cheers.

[JohnnyBGoode]

yeah - thanks so much Deecue - very much appreciated!