UV Map Sphere with relax texture
Create Sphere with Rhino
When you create a sphere in polygon mesh you need to approximate the shape. Rhino can UV Map a sphere directly but the UV Mapping is not very good. As you can see the UV Mapping on the sphere is not relax.
But you can UV map sphere sector by sector using cylindrical mapping.
A picture is good to explain but a 3D model is even better.
Download the 3DM
1st : Choose how many sector you want for your sphere shape.
6 is very rough and it's not very good
10 is good
12 much better
16 The current model (224 polygons. See Step 12)
18 You sphere now have good resolution
More give it a try but the result you will obtain
will have very high polygon count.
2nd step
Create a construction circle in the top view. Draw a circle with
the same radius of the sphere you want to create. And create a line from centre
to one of the quadrant.
3rd step
Copy-Rotate the line from step 2.
You need to calculate the rotation angle.
How ? Simple you want to create a sector of sphere.
Calculate the angle of this sector for this tutorial 16 sectors.
360º/16 = 22.5º /2 = 11.25º
Now copy rotate the line +11.25º and -11.25º
After you have rotated the lines create a line from end point to end point.
4th step
Now switch to Front view and create an ARC.
Create an ARC to control the sphere curve.
Centre = Centre of circle from step 2
Start point = Quadrant of circle from step 2
Angle = 90º
5th step
Move the Arc from step 4
Start Move command
Select the Arc
Point to move from: Select end point of the arc.
Point to move to : Select end point of one of the line you have rotated on step 3.
6th step
Create a Cylindrical Surface
Start Sweep 1 Rail Surface Command
Select rail curve : Select the line you have created at the end of step 3.
Select cross-section curves : Select the Arc you have moved on step 5.
7th step
Project line on Surface
Start Project curve on surface Command
Select points and curves to project : Select the line you have created on step
1.
Select surfaces or poly surfaces to project onto : Select the surface created
on step 6.
8th step
Create Surface to trim the Surface you created on step 6
Start Extrude Command
Select curves to extrude : Select the lines (2) you have rotated on step 2
Extrusion distance : Just make sure the extruded surface intersect the cylindrical
surface. (See the Magenta Surface on layer "Step 08".)
9th step
Trim the cylindrical Surface
Start Trim command
Select the cutting Object : Select the Extruded Surface you created on step 8.
Select object to trim : Click on surface outside the V surface.
(For the result see the surface on layer "Step 09").
Comments
In order to help you to create your texture for the trimmed surface from Step 9 you can "Unroll Surface". When you start this command Rhino generate a planar surface from the cylindrical surface.
This technique can be used on a complete Cylinder.
Why we need to unroll surface ?
It's just to help you to create your texture.
10th step
Unroll Developable Surface
Start Unroll Developable Srf Command
Select Surface or Poly-suface to unroll : Select the Trimmed surface from Step
9.
Select curves on Surface to unroll : Select the projected line created on step 7.
11th step
Create your texture.
Now you have two option to create your texture :
1. Create a screen shot of this planar surface Open your paint program and create
your texture.
2. Or create your texture by applying a basic texture on this planar surface
and add 3D elements to create all detail you want.
12th step
Create the polygon mesh
Now you need to choose how many division is needed to create the sphere.
For this tutorial we work on half sphere if you have chosen 16 sectors on step
1 try to obtain 7-8 polygon for 1 sector.
Start Mesh from Nurbs surface Command
Select surfaces or poly surfaces to mesh : Select the trimmed surface from step
9.
On Polygon Mesh Options Popup menu Click on Preview button and check the result : 32 polygons
It's to high, you need to reduce them.
Drag the Track bar to Fewer Polygons and try to have 7-8 polygons.
Use the Preview button to check the polygon count.
Why ? In order to have sphere with relative low polygon count.
You can calculate the polygon count before to create the sphere.
Formula :
16 sectors X 7 polygons = 112 polygons for the half sphere, and 224 polygons for the complete sphere.
After the polygon mesh is created hide the surface.
13th step
Apply texture on your mesh.
Start Object Properties Command
Select objects for properties editing : Select the polygon Mesh and press "Enter".
On Material TAB Activate Basic and Click on Texture Button and select your texture.
You can render this mesh to check if your texture is not upside down or rotated. In that case you need to rotate your texture to match the mesh.
14th step
Ask Rhino to create your sphere.
Switch on TOP View and start the Array Polar Command
Select object to array : Select the polygon mesh.
Make sure Object snap POINT option is activated.
Centre of polar array : Select the point of the point on the last triangle of
the mesh. ( Or you can select the centre of the circle created on step 2.)
Number of elements : Enter the number of sector you have chosen of step 1. (
16 )
Angle to fill : 360º
The half of the sphere is created. Click Render and check the result.
As you can see each sector is clearly visible. But the result you will obtain in the game is more beautiful.
Last modification on
28.08.2007 2:54
by Guillaume Saumure.