Bad Preview Image

Discussion in 'Bug Reporting' started by ttoinou, Mar 8, 2013.

  1. ttoinou
    ttoinou New Member
    Last edited: Mar 8, 2013
  2. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Missing geometry is usually the resulted of inverted or overlapping faces. Check out Netfabb, it has a check and a repair feature, and the basic version is free.
  3. ttoinou
    ttoinou New Member
    Oooh that was obvious I'm a noob.
    It works! But how come this process actually adds up volume ?
  4. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Inverted geometry has no volume. So when you make proper manifold geometry, it'll add that volume.
  5. stop4stuff
    stop4stuff Well-Known Member
    What Mike said.

    Basically, the missing parts are missing volume, put the missing parts back and the volume is not missing :)

  6. AmLachDesigns
    AmLachDesigns Well-Known Member
    What the guys above said.

    But unless it's not obvious:

    Shapeways get files in different formats, and even within the same formats people create models in different ways (single shell, multiple shell overlapping, multiple shell boolean'ed), so SW has to try and resolve these different models into a form that the printers can handle.

    With your model you saw that this process decided that part of your model did not work, so ignored it, and calculated the volume of the part that was ok. When you fixed your model, it recognised the extra geometry and recalculated the volume.

    And in case your actual question is why is it calculating the volume at all (which it probably wasn't, I know) it is in order to calculate the price, as except for ceramics the price of an object = handling charge + volume x unit volume price. Ceramics charge by surface area.
  7. ttoinou
    ttoinou New Member
    Hi all. Thanks for your answers.
    My model (before being repaired by netfabb) is just prism and "spheres" (discretized) that are colliding.

    @Youknowwho4eva : I don't see the link with inversion. My object is just in a thousands of little pieces ("multiple shell overlapping" just like AmLachDesigns said).

    @stop4stuff & AmLachDesigns : No !
    Shapeways compute the right price, according to netfabb volume, and even more (I don't know the doll / eur conversion but there is 1 euro more).
    The missing parts on the image are counted in the price (otherwise it would be like a third cheaper).

    Volume before repairing : 4.4 cm^3
    Volume after repairing : 5.9 cm^3

    That's weird because linking prisms (discretized cylinders) together should take back volume.

    And netfabb repairing is destroying my object (some edges are missing) !
    Last edited: Mar 9, 2013
  8. stop4stuff
    stop4stuff Well-Known Member
    NetFabb calculates the volume in the same manner as Shapeways, if parts are missing in NetFabb the missing parts are not counted in the volume calculation.

  9. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    The collision is most likely the problem. If your prisms sit face to face, this will result in 2 faces exiting in the same location. Netfabb (and shapeways repair software) will delete one face, and then try to make sense of the left over face. Make it so your faces don't exist in the same location. either shorten your prisms so they are still in the spheres, but not touching each other, or join them all together into one geometry before exporting and uploading.
  10. ttoinou
    ttoinou New Member
    Interesting ! (but netfabb displays well the object there is no part missing unlike with the Shapeways preview image.)

    @Youknowwho4eva : I forgot to draw the prisms' faces :rolleyes: .

    However I used the netfabb "simple repair" and this time it worked !
    My objects are "en route to the 3D printers" :p .
    Thank you all for the explanations.
  11. ttoinou
    ttoinou New Member
    Okay that issue is BACK !
    I'm creating a big object made of little cubes cutted by planes. The whole object is made of little plane-cutted tetrahedron AND a big object with only squares face. Theses objects touches each other and create an object in one piece at the end.
    The preview image sometimes doesn't render little tetrahedrons !
    On the left the meshlab preview and on the right the bad SW preview..

    Attached Files:

  12. stonysmith
    stonysmith Well-Known Member Moderator
    My suspicion is that your original model is not a single shell.
    The Shapeways import processes removes small shells that are below a certain size limit.
    It appears that you stacked a bunch of independent cubes and then sliced across them, leaving some of the shells very tiny.
    As was said before ... " join them all together into one geometry" ... you need to Boolean all your shells together into a single shell. Doing so would also drastically cut your triangle count and file size.

    You could try to see if that will fix it for you.
    Last edited: May 5, 2013
  13. ttoinou
    ttoinou New Member
    netfabb cloud doesn't work and netfabb software destroys my object.
    I'll end up by changing my cube-slicing algorithm...

    Interesting.. Is this just for the preview or also for the printing process ?
  14. stonysmith
    stonysmith Well-Known Member Moderator
    Generally, if it's missing from the preview, it will be missing from the final print also.
  15. ttoinou
    ttoinou New Member
    Ok I hope so otherwise there would be a fail in SW : you culd tear up your object into a lot of littles pieces to reduce the price :) .
    Do you know the volume of the smallest shell accepted by Shapeways in the STL import process ? Thanks.