To place nodes along the boundary of a closed shape

Select Place Nodes.
Select the appropriate color mask.
From the Entity option menu, choose Line or Outline.
Select Element as the Boundary option.

Note: This option is not accessible when there is no active image.
Identify the vector element to be used as a boundary. The element must be a closed shape.
If Line is chosen, nodes are placed everywhere the boundary of the element crosses raster lines. Outlines or edges are not considered.

If Outline is chosen, nodes are placed everywhere the boundary of the element crosses the edge of raster objects or lines. Both sides of raster lines are considered.

Both Raster Snap and Vector Snap toggles are disabled with this option.