hi: i have some question about normal and orientation
1-dose the normal give every fase of geometry (or maybe evry point , i don't know exactly ) a direction to the center of this geometry?
2-how to work with this parameter and how i can see the normal's vector to evry fase (or point)?
3-and in the attached file (normal 2) whin the orientation of circle1 is XY plane the circle is aligned to the evry point of the tube(making by loft) ideally,but when i change the orientation to this circle(circle1) to YZ or ZX plane the aligned take a strange form who i can't understand, any one can explain me how this happend and explane what is the orient of the geometry?

xoctan657
1-dose the normal give every fase of geometry (or maybe evry point , i don't know exactly ) a direction to the center of this geometry?

All primitives have an orientation based on the way Houdini stitches polygons from points. Basically the vertex order. You can't edit this normal. Well yes you can: move some points on the face.

You can assign a normal attribute to the points. Best done with the Facet SOP or the Point SOP.

xoctan657
2-how to work with this parameter and how i can see the normal's vector to evry fase (or point)?

Easiest way to work with point normals is the Point SOP. There you have direct access to the normal data. Please see the numerous example files for the Point SOP in the operator Help.

3-and in the attached file (normal 2) whin the orientation of circle1 is XY plane the circle is aligned to the evry point of the tube(making by loft) ideally,but when i change the orientation to this circle(circle1) to YZ or ZX plane the aligned take a strange form who i can't understand, any one can explain me how this happend and explane what is the orient of the geometry?
Houdini aims everything down the Z axis. You orient your geometry the way you want it to point with the Z axis. The Copy SOP will orient your geometry using it's Z axis and match that with the incoming point template normals.
See the numerous examples files for the Copy SOP in the operator Help. And please read the comments on the nodes (MMB on the tiles).

ok,thanks for answer,but
in the answer of the questions you say:
1-Houdini aims everything down the Z axis. You orient your geometry the way you want it to point with the Z axis. The Copy SOP will orient your geometry using it's Z axis and match that with the incoming point template normals.
how i can know how houdini orient the normals of point's geometry template,is it always to the Z axis .and you mean the Zaxis of the world space or the bounding box's center axis.and if i have a sphere ,are the normals of all points be aimed to the center of this sphere or not ?
2- You can't edit this normal. Well yes you can: move some points on the face.
i couldn't understand how to edit ,what you mean move some point on the fase which fase and which points
the oreint is controled what?
i have just one week working on the houdini and in the last i work with maya so ………….
3- See the numerous examples files for the Copy SOP in the operator Help. And please read the comments on the nodes (MMB on the tiles).
what is MMB and where i can read the comments i searched the houdini help for MMB but i don't find any thing,i am sorry ,but if you can explain to me more.thanks again

1) MMB is the middle mouse button
2) The normals of the default circle always point in the z-direction. The normal of a polygon in general is (usually) perpendicular to it.

Have a look at the sweep sop and the tutorial section about sweeps. They do explain a bit more about normals and orientating geometry on curves etc.

Pagefan ,thanks the video is very nice and help me very much ,but i still have some quistion
in the photo dowen i have circle1 in the XY plane and a tube who making by loft two circles (circle2) evry one from a 8 divisions
whin i copy the circle1 to the tube that is what happend and the quistion in the photo.

so anybody can give a compendium about the normal ………… please

Think there is nothing wrong with your picture. The geometry is copied on the lofted circles and orients itself to the normals of the points on the loft.

The normals on the copied circles aren't rotated, they just follow from the way the circles are orientated.

Pagefan ,look at to the picture down and you can notes how the
goemetry (circle1)have a rotation around the lofted circles's normals and the houdini file are in attached

hello xoctan,

There are a few things to note regarding your file, and a few general ‘3d’ related principles that need clarifying.

There are 2 kinds of normals (well… there are more, but in everyday use houdini use, there are 2).

The first kind is known in the houdini world as a primitive normal. The primitive normal is determined by the winding of the vertices (using the left-hand wound, or right-hand wound method, depending on your platform). This normal is determined mathematically, and for all intents and purposes can only be ‘reversed’. you can manipulate it, as someone mentioned but you have to deform the geometry, and have the system recompute it for it. this kind of normal is mathematically derived based on the positions of the vertices that make up a particular face.

The second kind of normal is known as the point normal, and it is ‘free-game’. you can compute it using the facet sop, OR, optionally, you can set it to be whatever you want. IIRC, the facet sop, will average neighboring primitive normals, and set the point normal to that, so in this context the point normal can be derived from the primitive normal.

Now, as for your particular issue, as you may already know, it takes 2 vectors to precisely orient a piece of geometry in 3d space. By convention these are called N and up. If you examine your geometry (mmb on the loft1 sop), you'll note that in your case, neither of those are defined – which means that houdini will go and do ‘something’ (that ‘something’ depends on the inputs and circumstances).

Take a look at the attached file, and note that when I added an additional up vector(point1 sop), the orientation of the circles gets ‘fixed’.

In this particular case, the N attribute, though not explicitly defined is derived from the geometry, and the up vector provides the extra vector along which to orient your circle.

Hope this helps,

G

ps: just for the record, the sweep sop (when used on a single circle) will do a better job by default. you can then simply copy the result, and endup in the same place. There are probably 100 ways to achieve this result… so you are likely to hear other approaches as well.

that is great (keyframe) . and i try to understand that,so if i have any question i will ask again

thank you very much this is very helpfull.

keyframe
can you give any link or any literature to read about this and know in-depth information…

keyframe
can you give any link or any literature to read about this and know in-depth information…

http://en.wikipedia.org/wiki/Surface_normal [en.wikipedia.org]
http://msdn.microsoft.com/en-us/library/bb324491(VS.85).aspx [msdn.microsoft.com] (OMG, actually something useful on a Microsoft site!)
http://en.wikipedia.org/wiki/Normal_component [en.wikipedia.org]

Actually there is a whole list about mathematical normals on wikipedia:
http://en.wikipedia.org/wiki/Normal_(mathematics) [en.wikipedia.org]

Have fun reading all that stuff