Truncating and re-saving a Mesh (in .stl format)

New to Julia
1

I would like to load a .stl file of triangular facets, remove most from the mesh and save as a new .stl file.

using FileIO, MeshIO
mesh = load("test.stl")
using GeometryBasics
new_mesh = Mesh(mesh[1:3])  # grab first three triangles
save("test_out.stl", new_mesh)

The code above fails with a method error. Other more detailed forms of setting up a new Mesh from the old have also met with issues deeper in GeometryBasics, so I must be missing something.

What is the accepted approach? Can someone provide a short working example of this?
Thanks!

2

Can you help by making the example reproducible?
What’s the method error?
It looks good in theory, but maybe just some wrongly ordered arguments or so… or a bug!

new_mesh = Mesh(mesh[1:3])

This could work, but is definitely untested :wink:

3

Thanks for the quick reply Simon! This code :

open("test.stl", "w") do io 
    write(io, "solid \n")
    write(io, " facet normal 1.0 1.0 1.0\n")
    write(io, "    outer loop\n")
    write(io, "        vertex 1.0 0.0 0.0\n")
    write(io, "        vertex 0.0 1.0 0.0\n")
    write(io, "        vertex 0.0 0.0 1.0\n")
    write(io, "    endloop\n")
    write(io, " endfacet\n")
    write(io, " facet normal 1.0 1.0 1.0\n")
    write(io, "    outer loop\n")
    write(io, "        vertex 2.0 0.0 0.0\n")
    write(io, "        vertex 0.0 2.0 0.0\n")
    write(io, "        vertex 0.0 0.0 2.0\n")
    write(io, "    endloop\n")
    write(io, " endfacet\n")
    write(io, " facet normal 1.0 1.0 1.0\n")
    write(io, "    outer loop\n")
    write(io, "        vertex 3.0 0.0 0.0\n")
    write(io, "        vertex 0.0 3.0 0.0\n")
    write(io, "        vertex 0.0 0.0 3.0\n")
    write(io, "    endloop\n")
    write(io, " endfacet\n")
    write(io, "endsolid \n")
end

using FileIO, MeshIO
mesh = load("test.stl")
using GeometryBasics
new_mesh = Mesh(mesh[1:2])  # grab first two triangles
save("test_out.stl", new_mesh)

will produce this error :

Error encountered while saving "test_out.stl".

Fatal error:
ERROR: LoadError: MethodError: no method matching coordinates(::Mesh{3,Float32,GeometryBasics.Ngon{3,Float32,3,PointMeta{3,Float32,Point{3,Float32},(:normals,),Tuple{Vec{3,Float32}}}},Array{GeometryBasics.Ngon{3,Float32,3,PointMeta{3,Float32,Point{3,Float32},(:normals,),Tuple{Vec{3,Float32}}}},1}})
Closest candidates are:
  coordinates(::GeometryBasics.Ngon) at /home/user/.julia/packages/GeometryBasics/csguK/src/basic_types.jl:73
  coordinates(::LineString) at /home/user/.julia/packages/GeometryBasics/csguK/src/basic_types.jl:187
  coordinates(::TupleView) at /home/user/.julia/packages/GeometryBasics/csguK/src/viewtypes.jl:39
  ...
Stacktrace:
 [1] handle_error(::MethodError, ::File{DataFormat{:STL_ASCII}}) at /home/user/.julia/packages/FileIO/2fEu2/src/error_handling.jl:82
 [2] handle_exceptions(::Array{Any,1}, ::String) at /home/user/.julia/packages/FileIO/2fEu2/src/error_handling.jl:77
 [3] save(::Formatted, ::Any; options::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /home/user/.julia/packages/FileIO/2fEu2/src/loadsave.jl:238
 [4] save at /home/user/.julia/packages/FileIO/2fEu2/src/loadsave.jl:217 [inlined]
 [5] #save#19 at /home/user/.julia/packages/FileIO/2fEu2/src/loadsave.jl:139 [inlined]
 [6] save(::String, ::Mesh{3,Float32,GeometryBasics.Ngon{3,Float32,3,PointMeta{3,Float32,Point{3,Float32},(:normals,),Tuple{Vec{3,Float32}}}},Array{GeometryBasics.Ngon{3,Float32,3,PointMeta{3,Float32,Point{3,Float32},(:normals,),Tuple{Vec{3,Float32}}}},1}}) at /home/user/.julia/packages/FileIO/2fEu2/src/loadsave.jl:139
 [7] top-level scope at /home/user/mesh_save_error.jl:36
 [8] include(::String) at ./client.jl:439
 [9] top-level scope at REPL[1]:1
in expression starting at /home/user/mesh_save_error.jl:36

on Julia v1.4.1 with recent packages :

...
  [5789e2e9] FileIO v1.4.4
...
  [5c1252a2] GeometryBasics v0.3.3
...
  [7269a6da] MeshIO v0.4.3
...