Interiors and exteriors when working with multipolygons

LarsDomesjö

Hello ESRI-community ,

I am working with creating a Geodatabase of buildings and have run into an issue I wanted to get straightened out.

I have a written a software to parse buildings from GML into ESRI geometries and then store them in a GDB/SDE, but I seem to be able to get the Shapes working properly for some of the more complex building bodies.

The more complex buildings get their GML-data split into multiple parts which I want to merge into one shape in ArcGIS Pro.

So I do this by first creating a Polygon for each part, then taking all those polygons and creating one Polygon out of them.

The Issue I am having however is that some of the polygons end up as interior holes and some as exteriors, see this sample:

I have read some documentation saying that the order of the points in the polygon is important, as depending on if they are CW or CCW will determine if it will be an interior or exterior ring.

I have ensured that the points are in the correct orientation but am still having the same issue.

I have read some other documentation saying that a polygon within an exterior polygon will always end up as an interior polygon, and a polygon within that interior polygon will end up as an exterior polygon and so on.

Could anyone give me some direction on this? I have created a sample application for this which i could attach if what I am trying to accomplish should be working but I have ran into some issue

Thanks!

Best regards

Lars

Wolf

Hi Lars, 

 Just to re-iterate the issue one more time: after converting a set of polygons from GML these polygons can be rendered as 'distinct' polygon records as shown below, showing all the expected detail (extrusions etc.): 

 

If we take these 'distinct' polygon records and create one 'multi-part' polygon record using the 'distinct' polygons as parts, the rendered representation has 'holes' as compared to the rendering of the 'distinct' records.

I showed the data to the development team and here is the gist of their reply:

ArcGIS Pro only renders multipart polygons without 'holes' if these polygons are 'simple' polygons.  One of the requirements of a 'simple' polygon is that 'rings cannot overlap'.  If there's an overlap of parts, rendering can exhibit 'holes' because ArcGIS Pro uses the even-odd rule when rendering polygons.  As defined by this rule overlapping parts will produce holes when rendered.  Here is a definition of the Even-Odd rule: https://en.wikipedia.org/wiki/Even%E2%80%93odd_rule

So in order to render the converted GML you have two options: add a 'distinct' polygon for each part of the building (and use an id field to identify polygons belonging to a specific building) or union the polygon parts of a building into a single building polygon (in which case you only get the footprint outline of the building).

For the next release, we will try to update our ProConcept documentation to address these rendering behaviors in more detail.