#### 3.25.53.3 scanorder

By default the quadrangles making up a pm3d solid surface are rendered in the order they are encountered along the surface grid points. This order may be controlled by the options ‘scansautomatic‘|‘scansforward‘|‘scansbackward‘. These scan options are not in general compatible with hidden-surface removal.

If two successive scans do not have same number of points, then it has to be decided whether to start taking points for quadrangles from the beginning of both scans (‘flush begin‘), from their ends (‘flush end‘) or to center them (‘flush center‘). Note, that ‘flush (center|end)‘ are incompatible with ‘scansautomatic‘: if you specify ‘flush center‘ or ‘flush end‘ and ‘scansautomatic‘ is set, it is silently switched to ‘scansforward‘.

If two subsequent scans do not have the same number of points, the option ‘ftriangles‘ specifies whether color triangles are drawn at the scan tail(s) where there are not enough points in either of the scan. This can be used to draw a smooth map boundary.

Gnuplot does not do true hidden surface removal for solid surfaces, but often it is sufficient to render the component quadrangles in order from furthest to closest. This mode may be selected using the options

          set pm3d depthorder hidden3d

The ‘depthorder‘ option orders the solid quadrangles; the hidden3d option similarly orders the bounding lines (if drawn). Note that the global option hidden3d does not affect pm3d surfaces.