Create polygon with hole

[Nguyễn Văn Mỹ]

I create polygons by Polygonizer class, but it can not create polygon with a polygon inside, it only create a polygon outside,

Sorry for my English

Thanks,

[Diego Guidi]

can you post an example of the code are you using?

[shawty]

What you need to do is create a MULTIPOLYGON not just a POLYGON

You can do it easily using the wktReader classes in NTS....

Create a string containing your polygon definition as shown here:

http://en.wikipedia.org/wiki/Well-known_text

Then once you have this string use a wktReader to convert it to an NTS geometry.

Shawty

[Nguyễn Văn Mỹ]

I am programing MicroStation Addmin, i load all line in a dgn file to List<LineString> and using code:

Polygonizer polygonizer = new Polygonizer();

                polygonizer.Add(listLines);

                var polys = polygonizer.GetPolygons();

It's ok, but can not get Polygon inside a polygon.

My solution: after get polygon, i scan line inside this polygon, then add to a List<LineString> listHoleLines, it's ok, using polygonizer again

Polygonizer holePolygonizer = new Polygonizer();

                        holePolygonizer.Add(listHoleLines);                        

                        var holePolys = holePolygonizer.GetPolygons();

but it allways return no polygon in holePolys.

thanks.

Vào 13:53:31 UTC+7 Thứ hai, ngày 13 tháng năm năm 2013, Diego Guidi đã viết:

[FObermaier]

You are getting polygon with holes and you want the hole-polygons as extra polygons?

 Why don’t you iterate over the resulting polygons, see if they have holes

   ((IPolygon)geom).NumInteriorRings > 0

and then build new polygons for the interior rings

   //…

  var f = geom.Factory;

  var p = (IPolygon) geom;

  var polys = new List<IGeometry>();

  foreach (var i = 0; i < p.NumInteriorRings; i++)

  {

      polys.Add(f.CreatePolyogn((ILinearRing)p.GetInteriorRingN(i), null));

[Nguyễn Văn Mỹ]

Hi FObermaier,

Thanks for your reply.

 I want to getting 2 polygons in this case. 

I iterate over the resulting polygons, but  ((IPolygon)geom).NumInteriorRings always return 0 for all polygons, seem like Polygonizer can not get InterriorRings. 
Thanks again, specially Sharpmap project, it's very usefull with me.

Vào 21:56:18 UTC+7 Thứ năm, ngày 07 tháng mười một năm 2013, FObermaier đã viết:

[FObermaier]

Could you provide the WKT of the polygonizer input geometries and result?

[Nguyễn Văn Mỹ]

Hi FObermaier,

I attach 2 files, Line.txt contain set of LineString from a dgn file, and Polygons.txt contain a set of Polygon after polygonizer.

My solution: I iterate over the resulting polygons, then get all linestrings inside this polygon (example 4 linestring) and polygonizer its (4 linestrings) again, 

i think GetPolygons() method will return 1 polygon but it return 0 polygon.

What wrong in my solution?

Thanks,

Vào 17:26:03 UTC+7 Thứ sáu, ngày 08 tháng mười một năm 2013, FObermaier đã viết:

[Nguyễn Văn Mỹ]

Hi FObermaier,

I am tested on different dgn files, method ((IPolygon)geom).NumInteriorRings do not return 0 if have a LinearRing inside polygon, but i only have a list of LineString. 

Vào 17:26:03 UTC+7 Thứ sáu, ngày 08 tháng mười một năm 2013, FObermaier đã viết:

[FObermaier]

You are -probably- not getting the desired result because the input linestrings are not all well connected.

For example the x-ordinate of the 2nd Point of the 2ndlast linestring and the x-ordinate of the 1st point of the last linestring are off by a tiny fraction.

Not knowing how you build your NTS geometries, you might want to use a scaled precision to avoid that.

[Nguyễn Văn Mỹ]

thanks for your reply.

Best regards, FObermaie

Vào 18:20:11 UTC+7 Chủ nhật, ngày 10 tháng mười một năm 2013, FObermaier đã viết: