I’m aware of the fact that Blender is not meant to be a powerful CAD-Tool, but I’d like to know if it is possible to add a flat or something with a plane bottom exactly tangentially to a curved surface? Like a cube on a sphere or so…
I’m about to add some windows to a plane, but these are not parallel to any main-axis.
basically it is possible with the power of viewport alignment and the 3D cursor. It´s a dirty method, but the result is CAD exact.
Lets say you got a uv sphere.
You cut a new ring-edgeloop, basically the meridian you want your tangent to be on.
Now select the point (vertex) you want the tangent to be.
Press shift+s and snap the cursor to the vertex.
select View>align view> selected> top.
now the view aligns, assuming Z is the normal at the point, in the YX plane of the point, matching your viewport with the tangent plane.
Now be sure to have selected in general preferences to add new objects at the location of the cursor and to match the view axis, not the global axis.
If you add for instance a plane now, it is exactly the tangent plane of your selected point.
It bears dangers though.
If you messed up your face/vertex normals by scaling non uniform in object mode, be sure to apply scale in object mode and recalculate all normals outside as well.
Else you might get false tangents and don´t notice it because the normals are off unoticable.
I can follow your instructions of the the first break, but after that I get a little bit confused, after I have matched my view normal to the selected vertex, my plane still appears normal to the main z-axis, I don’t really know what settings are exactly required…
Sorry for the sloppy explaination - it is hard to judge someone elses already aquired skills through the net.
I rather explain further if I get asked than giving step to step instructions down to the last bit.
You forgot to set in your user preferences to align the new object to your view axis rather than to the world axis.
As you see your plane is aligned with world XYZ.
You got to open your preferences “file>user preferences” or ctrl+alt+u
Then go to the “editing” tab and there you see in the leftmost column “align to:” and change it from “world” to “view”
When you add the plane then, it will be added in your view XY plane (assuming OpenGL standards and the depth of your view is the Z axis)
You might also want to press numpad5 to switch to ortographic view. Perspective view during modeling only fools ones eye and you loose your sense for proportion =)
The tangent plane for a face is the face itself, you simply would have to duplicate it and scale it up. That is so obvious that I didn´t take it into account.
I guess it is all about a tangent plane in a point on a curve, which is a vertex.
On a sidenode I think it would be a walk in a park for someone into python to create a “make tangent plane in selected vertex” plugin.
ok but as i said it’s kind of a prolbem cause edge and vertex dn’t really have a normal face
unless you follow the edge but again at which rotation do yu add the face or normal to it ?
They do.
There are vertex and edge normals as well, just because you can´t display them in blender doesn´t mean they are not there - they are basically actors behind the curtain
A vertex normal is the geometrical mean of the intersecting planes defining the vertex.
A edge normal is the geometrical mean of the intersecting planes defining the edge.
For instance when you switch an object from “solid” to “smooth” this is exactly what happens. The shading is not per face normal anymore, it is per vertex normal - actually it is per vertex before as well, the vertex normal just is the same vector as the faces’.
When you align your view “top” to a vertex you align it with this “invisible vertex normal”
The best advice to learn this stuff is to get some books on computer graphic, but be warned it is a broad topic, at university we had 3 different courses for it and 3 other ones for computer vision.
IMO the best place to start is the Khronos group
There are also many free resources on OpenGL, and in order to be able to work with OpenGL pretty much every detailed book about it covers the generic theory of computer graphic like shading, tangents, lighting, shadows, texturing, aliasing, texture filtering.
Also many universities offer good free papers on the topic.
And you really don´t need to be able to code to grasp the theory, but it brings you a step closer to understanding how and why some things work the way they do and why some don’t.
Personally I read the OpenGL Redbook and Bluebook along with some books about graphic engines and computer graphic in general.
Unfortunately those kind of technical books are rather expensive so you can´t just buy one out of the blue, you really need to know what you are after.
If you want a nice starting point in the wikipedia this is a good place to start:
If you follow the links there you´ll get a lot of shading methods and other stuff explained. Within 10 minutes you´ll have 1000 tabs open all with wiki articles and you´ll see what mess you got yourself into