You can map an image to a cylinder, but not to half a sphere without
some distortion. I cannot successfully import your wallpaper image into
openscad, but if you can, it will probably not appear where you expect
it to.  With your image, if successfully imported, parts are likely to
fall out, if punched right through. I've shown a bit of code, some to
generate an SVG that openscad can handle, although as usual, it is
shifted. The other uncommented code punches it through a thin dome. I
think that is the simplest solution. It may be better if your image was
distorted, so that it was compressed at the edges, and expanded in the
centre.  Of course, you could cut the image more or less into triangles,
and treat the sphere as some other shape with flat faces.

  intersection(){
difference(){
        sphere(50/2);
        sphere((50/2)-2);
           }
       pat();
 }

/*
module svg(){
            difference(){
                square(50,true);
                    translate([-10,-10])circle (d=4);
                     circle(d=3);
                        translate([10,10])circle (d=4);
                         translate([15,8])circle (d=4);
                        translate([-20,20])circle (d=4);
                        translate([-10,10])circle (d=4);
           }
}
svg();
*/

module pat(){
    translate([-25,-75,0]) // to make svg centered
       linear_extrude(30)
         import("C:/Users/ray/Documents/pat.svg");
}

On 31/05/2024 11:38, Karl Exler via Discuss wrote:

Am 31.05.24 um 12:38 schrieb Karl Exler via Discuss:

a half sphere. The idea is to put it on a LED light and have beautiful
shadows on the wall.

Maybe you should read https://en.wikipedia.org/wiki/Map_projection .
This is the reverse operation (Sphere to plane), but it may show up
possible issues with these kind of operations to you. And maybe it give
you some ideas, how to solve your problem.

Are you trying to make a cutout or apply a texture to make something with
thin and thick regions?  You can probably apply a texture using the BOSL2
texturing capability with rotate_sweep().  I feel like this specific topic
(maybe even with a world map example) was discussed here kind of
recently.  This would require converting the SVG to a bitmap which you
then use as the texture input.

https://github.com/BelfrySCAD/BOSL2/wiki/skin.scad#functionmodule-rotate_sweep

On Fri, May 31, 2024 at 6:39 AM Karl Exler via Discuss <
discuss@lists.openscad.org> wrote:

I tried this today:
file can be downloaded from here:
https://github.com/sprabhakar2006/openSCAD/blob/main/points_on_sphere.scad

[image: Screenshot 2024-06-01 at 5.26.51 PM.png]

On Fri, 31 May 2024 at 16:09, Karl Exler via Discuss <
discuss@lists.openscad.org> wrote:

this makes a little more sense:

[image: Screenshot 2024-06-01 at 5.55.21 PM.png]

On Sat, 1 Jun 2024 at 17:29, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:

Instead of getting just coordinates, it would be interesting to learn, how
you map the coordinates onto the sphere.
Another promising idea could be to blow up  8 equiliteral triangles of an
octaeder to 8 eight's of a sphere.

On Sat, Jun 1, 2024 at 2:28 PM Sanjeev Prabhakar via Discuss <
discuss@lists.openscad.org> wrote:

Main idea is to be able to find intersection points.
Straight lines upwards are drawn from each point and then the intersection
is found.

On Sun, 2 Jun, 2024, 2:24 am Guenther Sohler via Discuss, <
discuss@lists.openscad.org> wrote:

That is what my earlier code snippet did, except my openscad would not
handle op's .SVG file. However, a more precise method would be to
'paint' the pattern on the walls and ceiling, position the led where you
want it, then ray-trace from that point to the pattern, and intersect
whatever shape of 'lamp shade' you wanted (figuratively speaking). I
can't do that in 'pure' openscad.

On 02/06/2024 01:46, Sanjeev Prabhakar via Discuss wrote:

tried it today once again, just to cover a larger area of sphere:
file can be downloaded from here:
https://github.com/sprabhakar2006/openSCAD/blob/main/points_on_sphere_rev1.scad
[image: Screenshot 2024-06-03 at 8.59.06 PM.png]

On Sun, 2 Jun 2024 at 06:16, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote: