CGAL users discussion list

[Claus Volko <>]

We are trying to make OBJ files saved from Google Maps HD compatible with CGAL 5.6 for Shape Detection (Region Growing). On opening the OBJ file I get an error message that does not explain what is wrong, but after converting to OFF it is more verbose:

CGAL::Polyhedron_incremental_builder_3<HDS>::
lookup_halfedge(): input error: facet 49 shares a halfedge from vertex 145 to vertex 146 with facet 48.

Polyhedron_scan_OFF<Traits>::
operator()(): input error: facet 50 has fewer than 3 vertices.
ERROR: cannot read the input file!

I wrote a short program in C# that should fix the problem (attached). However, the result is a file that is somewhat degenerated: the number of planes is equal to the number of faces. This cannot be used.

Does anybody have an idea how else this could be fixed?

--

Dipl.-Ing. Dr. Claus D. Volko, BSc
http://www.cdvolko.net/

using System.Globalization;
using System.Security.Cryptography;

var input = new StreamReader(new FileStream("c:\\temp\\Scene.obj", 
FileMode.Open));
var output = new StreamWriter(new FileStream("c:\\temp\\scene.txt", 
FileMode.Create));
var s = "";
var listVertices = new List<int>();
while (!input.EndOfStream)
{
    var s0 = input.ReadLine();
    s = s0;
    if (!s.StartsWith("f "))
    {
        output.WriteLine(s);
        continue;
    }
    s = s[2..];
    var v0 = parseVertex(s[..s.IndexOf(" ")]);
    s = s[(s.IndexOf(" ") + 1)..];
    var v1 = parseVertex(s[..s.IndexOf(" ")]);
    s = s[(s.IndexOf(" ") + 1)..];
    var v2 = parseVertex(s);
    var b0 = listVertices.Contains(v0);
    var b1 = listVertices.Contains(v1);
    var b2 = listVertices.Contains(v2);
    if ((b0 && b1) || (b1 && b2) || (b2 && b0)) continue;
    if ((v0 == v1) || (v1 == v2) || (v2 == v0)) continue;
    listVertices.Add(v0);
    listVertices.Add(v1);
    listVertices.Add(v2);
    output.WriteLine(s0);
}

output.Close();

int parseVertex(string s)
{
    if (!s.Contains("/")) return int.Parse(s);
    s = s[..s.IndexOf("/")];
    return int.Parse(s);
}