Mesh manipulation in programming

Motivation

Apart from manual mesh manipulation of mesh in apps and tool like netfabb Studio, it is also possible to manipulate mesh with code - creating programs, that manipulate meshes in some more ro less interesting manner. It would be sad not to examine this topic as well being on the Faculty of Information Technology.

ADMesh

ADMesh is open-source CLI tool for STL mesh manipulation and simple repairs. Apart from CLI, there is also C library API.

Short example follows. This loads model.stl (binary or ASCII) and rewrites is as ASCII or binary STL - it converts binary to ASCII and vice versa.

#include <stdlib.h>
#include <admesh/stl.h>

int main(void) {
  stl_file stl_in;
  char *filename = "model.stl";

  printf("Opening %s\n", filename);
  stl_open(&stl_in, filename);
  stl_exit_on_error(&stl_in);

  if (stl_in.stats.type == binary) {
    printf("Writing ASCII file %s\n", filename);
    stl_write_ascii(&stl_in, filename, "ADMesh");
    stl_exit_on_error(&stl_in);
  } else {
    printf("Writing binary file %s\n", filename);
    stl_write_binary(&stl_in, filename, "ADMesh");
    stl_exit_on_error(&stl_in);
  }

  stl_close(&stl_in);
  return EXIT_SUCCESS;
}

Notice that:

Compile the source with:

gcc source.c -ladmesh

Eventually, if your ADMesh installation is not in your standard PATH:

gcc -L/dir/with/so -I/dir/with/h source.c -ladmesh

We cannot provide instructions for Windows, use standard programming tools for C as if you would like to use any other library.

All structs and function can be found in the header file admesh/stl.h. Unfortunately, there is no documentation.

Task

To get 3 points, program C, C++ or Python tool, that will determine best possible rotation around Z axis for the given file (as first command line argument). Best rotation in this case is such rotation, when the area of smallest rectangle with sides parallel to X and Y axis, that can embrace the 3D model, is smallest.

Look at the bottom side of green cuboid (only corners are drown) - that’s our rectangle.

The app will print the best rotation (in degrees) to it’s standard output. It will also save a rotated version of the STL to a second file (second command line argument) - it will be saved in the same format (binary/ASCII) as was the input file loaded. Rotated version will be rotated by the exact same angle as the tool printed.

Best angle can be determined by brute force with angles dividable by 5° (5°, 10°, 15°, …​).

Useful functions and data: