'Return the length of one pixel in the direction indicated (in local coordinates)
If ortho=True, then return the length of one pixel orthogonal to the direction indicated.
Return None if pixel size is not yet defined (usually because the item has not yet been displayed).'

def pixelLength(self, direction, ortho=False):

    (normV, orthoV) = self.pixelVectors(direction)
    if ((normV == None) or (orthoV == None)):
        return None
    if ortho:
        return orthoV.length()
    return normV.length()
