How to fix this artifact?

[jellowone]

The artifact is highlighted by the red arrow in both the model and the rendering.  The window should be open but there appears to be a film covering the outside.  Does anyone know what cause this and how to get rid of it?

Thanks!

[loganfoster]

My guess is that you have one hell of a nasty ngon there. An ngon is a poly/face that is made up of more than 4 edges. nGons are bad because you are relying on the software or gpu to figure out how it needs to convert the many sided face into triangles (the basis of all visible geometry), and one of the telling signs of this being a problem is what you see on your photo.

How to fix this is to force quads or triangles into that nGnon. This is easily done through ePoly functions like connect, but there are lots of various ways that you can do it. The only downside is that this might take a bit of time. 

Note: You can get away with nGnons at times with your models sometimes (though they are best to be avoided), but the slightest change in vertex positions or angles to how the software/gpu triangulates the mesh will potentially visually break the model. 

[leeminardi]

How did you construct the window?  If you used a Boolean subtract it is possible to get infinitely thin surfaces if the object being subtracted was flush with the surface of the geometry you are subtracting it from.  One solution is to make sure the object being subtracted fully penetrates the model before giving the subtract operation.

As for the model, if it is an editable mesh  you can try offending faces or if it is  an editable poly try deleting offending Polygons.  You may have to create some new faces or polygons after the deletion but you should have the vertices you need to simplify this task.

[jellowone]

Thanks for all the replies.  I do agree that one problem is the ngons is forcing the software to figure out a lot of things which frequently fails.  In this case how to link the window to the rest of the plane which it sits on.

As to it being Boolean with an object that not fully penetrate the model, this was not the case as the artifact was not there when I first Boolean the model but came later when I manipulated the model – I suspect because of the problem mentioned in the above paragraph.

The good news is I found an easy fix for it.  Basically the idea is to not allow the software to figure things out but to do it yourself.  In this specific case, I did a QUICKSLICE on the face of the model across the plane where the two windows existed – this put in edges that links the windows to the rest of the plane and immediately fixed the problem