Empathy List Archives

GM

Gábor Magyar

Tue, Jun 4, 2024 9:14 AM

https://tool.itslitho.com/

Sanjeev Prabhakar via Discuss discuss@lists.openscad.org ezt írta
(időpont: 2024. jún. 3., H, 17:35):

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:

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:

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:

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:

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:

Dear all
I have an SVG file (see attachement) and I would like to attach it to
a
half sphere. The idea is to put it on a LED light and have beautiful
shadows on the wall.

many thanks
Karl

OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org

https://tool.itslitho.com/ Sanjeev Prabhakar via Discuss <discuss@lists.openscad.org> ezt írta (időpont: 2024. jún. 3., H, 17:35): > 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: > >> 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: >> >>> 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: >>> >>>> 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: >>>> >>>>> 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: >>>>> >>>>>> Dear all >>>>>> I have an SVG file (see attachement) and I would like to attach it to >>>>>> a >>>>>> half sphere. The idea is to put it on a LED light and have beautiful >>>>>> shadows on the wall. >>>>>> >>>>>> many thanks >>>>>> Karl >>>>>> _______________________________________________ >>>>>> OpenSCAD mailing list >>>>>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>>>>> >>>>> _______________________________________________ >>>> OpenSCAD mailing list >>>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>>> >>> _______________________________________________ >>> OpenSCAD mailing list >>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>> >> _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org >

KE

Karl Exler

Tue, Jun 4, 2024 10:21 AM

many thanks to all, for their great hints
Karl

Am 04.06.24 um 11:14 schrieb Gábor Magyar via Discuss:

https://tool.itslitho.com/

Sanjeev Prabhakar via Discuss discuss@lists.openscad.org ezt írta
(időpont: 2024. jún. 3., H, 17:35):

 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
 Screenshot 2024-06-03 at 8.59.06 PM.png

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

         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:

             this makes a little more sense:

             Screenshot 2024-06-01 at 5.55.21 PM.png

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

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

                 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:

                     Dear all
                     I have an SVG file (see attachement) and I
                     would like to attach it to a
                     half sphere. The idea is to put it on a LED
                     light and have beautiful
                     shadows on the wall.

                     many thanks
                     Karl
                     _______________________________________________
                     OpenSCAD mailing list
                     To unsubscribe send an email to
                     discuss-leave@lists.openscad.org

             _______________________________________________
             OpenSCAD mailing list
             To unsubscribe send an email to
             discuss-leave@lists.openscad.org

         _______________________________________________
         OpenSCAD mailing list
         To unsubscribe send an email to
         discuss-leave@lists.openscad.org

 _______________________________________________
 OpenSCAD mailing list
 To unsubscribe send an email to discuss-leave@lists.openscad.org

OpenSCAD mailing list
To unsubscribe send an email todiscuss-leave@lists.openscad.org

many thanks to all, for their great hints Karl Am 04.06.24 um 11:14 schrieb Gábor Magyar via Discuss: > https://tool.itslitho.com/ > > Sanjeev Prabhakar via Discuss <discuss@lists.openscad.org> ezt írta > (időpont: 2024. jún. 3., H, 17:35): > > 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 > Screenshot 2024-06-03 at 8.59.06 PM.png > > On Sun, 2 Jun 2024 at 06:16, Sanjeev Prabhakar > <sprabhakar2006@gmail.com> 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: > > 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: > > this makes a little more sense: > > Screenshot 2024-06-01 at 5.55.21 PM.png > > On Sat, 1 Jun 2024 at 17:29, Sanjeev Prabhakar > <sprabhakar2006@gmail.com> wrote: > > I tried this today: > file can be downloaded from here: > https://github.com/sprabhakar2006/openSCAD/blob/main/points_on_sphere.scad > > 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: > > Dear all > I have an SVG file (see attachement) and I > would like to attach it to a > half sphere. The idea is to put it on a LED > light and have beautiful > shadows on the wall. > > many thanks > Karl > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to > discuss-leave@lists.openscad.org > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to > discuss-leave@lists.openscad.org > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to > discuss-leave@lists.openscad.org > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org > > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email todiscuss-leave@lists.openscad.org

HL

Hans L

Wed, Jun 5, 2024 8:46 PM

Depending on how you map a rectangular image to the surface of a sphere, it
may distort greatly.

If you want to be able to recreate the undistorted image in the projection,
you need to do what is called a "stereographic projection"
https://en.wikipedia.org/wiki/Stereographic_projection

There are a number of examples online of projecting grids from spheres
etc.
https://www.youtube.com/watch?v=uuewH450Nag

Note that the light source should be as close to an ideal "point
light" source, and that the projection is very sensitive to the exact
position of the light.

On Tue, Jun 4, 2024 at 5:22 AM Karl Exler via Discuss <
discuss@lists.openscad.org> wrote:

many thanks to all, for their great hints
Karl
Am 04.06.24 um 11:14 schrieb Gábor Magyar via Discuss:

https://tool.itslitho.com/

Sanjeev Prabhakar via Discuss discuss@lists.openscad.org ezt írta
(időpont: 2024. jún. 3., H, 17:35):

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:

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:

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:

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:

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:

Dear all
I have an SVG file (see attachement) and I would like to attach it
to a
half sphere. The idea is to put it on a LED light and have beautiful
shadows on the wall.

many thanks
Karl

OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org

Depending on how you map a rectangular image to the surface of a sphere, it may distort greatly. If you want to be able to recreate the undistorted image in the projection, you need to do what is called a "stereographic projection" https://en.wikipedia.org/wiki/Stereographic_projection There are a number of examples online of projecting grids from spheres etc. https://www.youtube.com/watch?v=uuewH450Nag Note that the light source should be as close to an ideal "point light" source, and that the projection is very sensitive to the exact position of the light. On Tue, Jun 4, 2024 at 5:22 AM Karl Exler via Discuss < discuss@lists.openscad.org> wrote: > many thanks to all, for their great hints > Karl > Am 04.06.24 um 11:14 schrieb Gábor Magyar via Discuss: > > https://tool.itslitho.com/ > > Sanjeev Prabhakar via Discuss <discuss@lists.openscad.org> ezt írta > (időpont: 2024. jún. 3., H, 17:35): > >> 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: >> >>> 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: >>> >>>> 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: >>>> >>>>> 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: >>>>> >>>>>> 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: >>>>>> >>>>>>> Dear all >>>>>>> I have an SVG file (see attachement) and I would like to attach it >>>>>>> to a >>>>>>> half sphere. The idea is to put it on a LED light and have beautiful >>>>>>> shadows on the wall. >>>>>>> >>>>>>> many thanks >>>>>>> Karl >>>>>>> _______________________________________________ >>>>>>> OpenSCAD mailing list >>>>>>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>>>>>> >>>>>> _______________________________________________ >>>>> OpenSCAD mailing list >>>>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>>>> >>>> _______________________________________________ >>>> OpenSCAD mailing list >>>> To unsubscribe send an email to discuss-leave@lists.openscad.org >>>> >>> _______________________________________________ >> OpenSCAD mailing list >> To unsubscribe send an email to discuss-leave@lists.openscad.org >> > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org >

CM

Curt McDowell

Wed, Jun 12, 2024 8:48 PM

On 6/5/2024 1:46 PM, Hans L via Discuss wrote:

Depending on how you map a rectangular image to the surface of a

sphere, it may distort greatly.

If you want to be able to recreate the undistorted image in the

projection, you need to do what is called a "stereographic projection"

https://en.wikipedia.org/wiki/Stereographic_projection

If the idea is to have a distorted image on the sphere that projects an
un-distorted image on a wall, one idea would be to assume a point light
source at the center of the sphere, project rays from there to each
pixel of the image on the wall, mathematically calculate the
intersection of the rays with the surface of the sphere, and punch holes
there. Then a point light source should project through the holes to
form the image on the wall. The clarity of the projected image might
vary because of quantum interference effects and limited transmission
efficiency, depending on the size of the holes and other factors.

I wrote some code for this and have attached the interesting function
line_sphere_intersection(p1, p2, center, r).

For example:

The (idealized) result of projecting the phallus wallpaper from this
sphere would look like this:

Unfortunately OpenSCAD F6 cannot render this sphere. It takes days or
weeks using CGAL, and with Manifold it quickly consumes gigabytes of
memory until the process gets killed (maybe it's a similar problem to
#5069 https://github.com/openscad/openscad/issues/5069?) It seems like
it would be really hard to 3D print anyway.

This one is simpler but maybe also hard to 3D print:

Manifold can handle it easily:

Regards,
Curt

On 6/5/2024 1:46 PM, Hans L via Discuss wrote:

Depending on how you map a rectangular image to the surface of a
sphere, it may distort greatly.

If you want to be able to recreate the undistorted image in the
projection, you need to do what is called a "stereographic projection"
https://en.wikipedia.org/wiki/Stereographic_projection

There are a number of examples online of projecting grids from spheres
etc.
https://www.youtube.com/watch?v=uuewH450Nag

Note that the light source should be as close to an ideal "point
light" source, and that the projection is very sensitive to the exact
position of the light.

On 6/5/2024 1:46 PM, Hans L via Discuss wrote: > Depending on how you map a rectangular image to the surface of a sphere, it may distort greatly. > > If you want to be able to recreate the undistorted image in the projection, you need to do what is called a "stereographic projection" > https://en.wikipedia.org/wiki/Stereographic_projection If the idea is to have a distorted image on the sphere that projects an un-distorted image on a wall, one idea would be to assume a point light source at the center of the sphere, project rays from there to each pixel of the image on the wall, mathematically calculate the intersection of the rays with the surface of the sphere, and punch holes there. Then a point light source should project through the holes to form the image on the wall. The clarity of the projected image might vary because of quantum interference effects and limited transmission efficiency, depending on the size of the holes and other factors. I wrote some code for this and have attached the interesting function *line_sphere_intersection(p1, p2, center, r)*. For example: The (idealized) result of projecting the phallus wallpaper from this sphere would look like this: Unfortunately OpenSCAD F6 cannot render this sphere. It takes days or weeks using CGAL, and with Manifold it quickly consumes gigabytes of memory until the process gets killed (maybe it's a similar problem to #5069 <https://github.com/openscad/openscad/issues/5069>?) It seems like it would be really hard to 3D print anyway. This one is simpler but maybe also hard to 3D print: Manifold can handle it easily: Regards, Curt On 6/5/2024 1:46 PM, Hans L via Discuss wrote: > Depending on how you map a rectangular image to the surface of a > sphere, it may distort greatly. > > If you want to be able to recreate the undistorted image in the > projection, you need to do what is called a "stereographic projection" > https://en.wikipedia.org/wiki/Stereographic_projection > > There are a number of examples online of projecting grids from spheres > etc. > https://www.youtube.com/watch?v=uuewH450Nag > > Note that the light source should be as close to an ideal "point > light" source, and that the projection is very sensitive to the exact > position of the light.

discuss@lists.openscad.org

half sphere with pattern