Using Cut Sections Under OpenGL in 3D Mode

Using cut sections under OpenGL in 3D mode

D3PLOT has always displayed deformed space (Eulerian) cut sections correctly because they are flat and OpenGL provides "clipping planes" that will intersect the model correctly. D3PLOT still has to synthesise the cut surfaces of solids and capping polygons for shells, but the hardware has looked after the rest of the problem.

However prior to D3PLOT 10.0 basic space (Lagrangian) planes, which cease to be flat once the model deforms, have not been rendered correctly in OpenGL 3D mode. The cut surfaces through solids and the capping polygons for shells were displayed correctly, but the intersection of the rest of the model with the plane worked on the deformed space (flat) plane in 3D mode, which was in the wrong place, and gave a "jagged edge" effect in 2D mode.

From D3PLOT 10.0 onwards this limitation has been removed, and basic space cut sections now render correctly in 3D graphics mode.

The intersection between the plane and elements with a determinate topology (solids, shells, thick shells, beams, springs, seatbelts) is calculated individually for each item, and the fraction of the symbol which should be visible on the "drawn" side of the plane is shown correctly.

Nodes themselves, and elements with only a single node (SPH elements, masses, spotwelds, etc), are treated as being either "wholly visible" or "wholly clipped" by the plane and are drawn in full or not drawn accordingly. This logic is also applied to items without a determinate topology (eg joints, rigidwalls) and to composite elements such a spotweld clusters. This means that their symbols, which are of finite size, will pop into and out of view as the plane crosses them rather than being intersected gradually. This is not strictly correct, but it is acceptable and - more to the point - is fast to process and gives good graphics speeds.