2018-03-02 There is a new implementation of this object.
This is a python script to map a grayscale image as a height map onto the inside of a hollow sphere. The result is a spherical lithophane with a smooth outside.
- since the globe is quite small at the bottom I chose to use rafts for my first print - it would be a shame if anything fell over after 30 hours of printing
- you don't want to see any fill pattern shine through the walls and the whole concept of a lithophane depends on a solid wall
- on the other hand don't forget that the globe itself is hollow - the 100% infill only affects the wall of the globe
A couple of days ago I saw the YouTube video where RCLifeOn presented his spherical lithophane globe. He used Autodesk 3ds Max to design the object, where he placed the height map on the outside of the globe, but I immediately wondered how it would look like when the height map was hidden inside the globe.
I din't see before now that RCLifeOn also posted his globe here on Thingiverse.
Free and open source?
Not having access to this piece of software I researched if I could get a similar result using free tools. My favorite OpenSCAD does not (yet?) support mapping of bitmap files onto non-flat surfaces, so I had to look further.
I quickly found an example on how to create an .stl file in python and started to experiment. My first output was a simple cube, before I put all pieces together:
- scaling an image
- creating a sphere
- creating a second sphere
- putting the two spheres into each other
- modifying the thickness of the wall by means of the map
Once I got the orientation of the faces correct and also succeeded in putting the image data the correct way onto the spheres, I let my script run for an hour or so and created the mesh for a 120 mm diameter globe, which has now been on the printer for 24 hours with about 10 hours left to go according to Octoprint.
The map I use is the free height map image of the world by NASA.
I then took the time to fine tune the script a bit and add some comments for readability.
# user settings
dia = 120
depth = 3
wall = 0.8
latsteps = 600
longsteps = 1200
openingNdeg = 20 # opening x degrees from north pole
openingSdeg = 130 # opening x degrees from south pole
- dia is the diameter of the final globe in mm
- depth is the maximum variation of the thickness of the globe's wall
- wall is the minimum remaining thickness of the wall
- latsteps is the number of steps from north to south
- longsteps is the number of steps along the equator
- openingNdeg is the size of an optional opening at the north pole
- openingSdeg is the size of an optional opening at the south pole
The above example settings produce a narrow rim of the globe between 40°N (=-90+130) and 70°N (=90-20) for testing purposes.
pre-rendered .stl files
- lithophane_world_closed.stl complete world, 120mm diameter, no holes, 300 latitude steps, 600 longitude steps
- lithophane_sphere_outside low-resolution, mapped on the outside of the sphere
Work in progress
- 2018-01-24 started printing
- 2018-01-25 still printing while writing this Thing
- 2018-01-26 also uploaded a script to generate the map on the outside of the sphere