Apologies for the newbie question.

I would like to inset a circle using the following nodes:

Circle (Radius 0.82, 0.82, 24 Divisions)
Polyextrude (Inset 0.02) - Works fine
Polyextrude (Inset 0.6) - This seems to be producing shading errors

Am I missing something here?


Clayton

Houdini Apprentice 21.0.631

Your second extrusion is extruding everything coming into that node - so you're getting overlapping polys.
On your second extrusion you just want to inset that inner poly.

To do so:
In extrusion one: enable the 'front group' option in the 'Output geo and groups' section.
In extrusion two: select that group - 'extrude front' - from the group drop down menu.

These aren't shading errors, but geometry overlap. If you set the distance to 0.3 in the second extrusion, you'll see this overlap. Make the inset negative to understand what's happening. The trick is that each node is independent and doesn't know what came before it. Insets require specifying a group or polygon numbers where they should be inserted, otherwise they'll be inserted everywhere. The first polyextrusion works with a single polygon, so there's no choice. The second polyextrusion receives multiple polygons, and you don't specify where to insert, so it tries to take the entire group and create a new inset from the edge, which all gets mixed up. But you probably want to continue insetting the center. For such a simple polygon, it's easier to select this polygon by clicking the arrow to the right of the Group field (it's the first one in the parameters). Generally, when you create the first polyextrusion, you need to enable the creation of the Front Group—this is the center of the inset or extrusion. Then, in the next extrusion, you need to select this group in the top group field, and the operation will be applied to it. And so on. Your entire chain will work with this group. Then, if you change the starting polygon, the number of segments, or anything else that changes the polygon numbering, everything will automatically rebuild. Generally, remember that 1) all nodes are independent, 2) you need to specify groups or specific polygon/point/edge numbers for operations, 3) if you change the input geometry, the polygon numbering will change, and everything will work incorrectly, 4) to avoid this, work with automatic or manual groups as much as possible. Then you only have to change the group contents at the beginning, and everything will change automatically. This will save you a ton of effort in long operations. But for simple operations, this is too redundant, and it's easier to select specific polygons and specify specific numbers—it's faster.

Many thanks both!! It worked!

I made sure that both output front and output side were checked during the extrusion. My mistake was having output back checked which produces overlapping geometry on a 2-dimensional surface.

What is also good about this method is that I do not have to add a blast node to delete the final centre face, I simply unchecked output front. I also didn't realise you can remove the actual inset itself by unchecking the output side and keeping the output front checked.