16. What are the HIN extensions that Molecule Presentations uses for orbitals?

The extensions for storing orbital information are:

IsosurfaceValue:  The value which the isosurface represents.  The
                  isosurface is built up from interpolating between
                  the values on the grid points to find point in space
                  with this value.

OrbitalRendering: 0 for mesh, 1 for unshaded polygons, 2 for shaded polygons.

GridStepCount:    The three integers give the number of points in the x,
                  y, and z directions (multiply the three to get the
                  total number of grid points).

GridStepSize:     This real number gives the increment (in Angstrom)
                  between grid points for each of the x, y, and z directions.

GridOrigin:       This gives the starting point for the grid (i.e. the
                  point with the lowest x, y, and z coordinates).

GridData:         The values for the grid points, in the order of z
                  varying fastest, then y and x varying slowest.
                  Note that one set of data may span several lines
                  but each line begins with "GridData" so that HyperChem
                  can ignore it (it is just for line width that there
                  are six numbers per line).

Some (non-optimal!) psuedo code for reading in the grid would be:

iPoint=0
for ix=1 to GridStepCount(1)
    x_coord = GridOrigin(1) + (ix-1)*GridStepSize
    for iy=1 to GridStepCount(2)
        y_coord = GridOrigin(2) + (iy-1)*GridStepSize
        for iz=1 to GridStepCount(3)
            z_coord = GridOrigin(2) + (iz-1)*GridStepSize
            iPoint = iPoint + 1
            Value = GridData(iPoint)
        end for
    end for
end for

This question has come up from users wishing to use ChemPlus to plot isosurfaces of the density or other properties.

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