Hi,
Rendering a number of identical isosurfaces, I noticed that one of them was
'missing'.  The problem seems to be based on a number of things - the
placement of  the object, the camera position, and bizarrely, a rotation
about the axis of symmetry which should produce no noticeable difference.
Checking the messages thread, it claims that the maximum gradient found was
0, and also lists all intersection tests with the isosurface as failing.

The other isosurfaces appeared exactly as they should, even in areas that
overlap where the 'vanished' isosurface should be.

I'm using version 3.6.1, on Windows 2000

camera {

    //orthographic

    location <4,8,10>

    direction <0,0,8>

    right <16,0,0>

    up <0,12,0>

    look_at <0,0,0>

}

#declare PentaToroid=object{

    isosurface{

        function{

            pow(sqrt(pow(x,2) + pow(z,2)) - 3 + (pow(z,5) -
10*pow(z,3)*pow(x,2) + 5*z*pow(x,4)) / pow(sqrt(pow(x,2) + pow(z,2)),5),2)
+ pow(y - (pow(x,5) - 10*pow(x,3)*pow(z,2) + 5*x*pow(z,4)) /
pow(sqrt(pow(x,2) + pow(z,2)),5),2) - 0.04

        }

        contained_by{box{<4.2,1.2,4.2><-4.2,-1.2,-4.2>}}

        evaluate 0.64*270,1.25,0.7

        all_intersections

        accuracy 0.001

        texture{T_Wood1}

    }

}
object{PentaToroid translate y*5 rotate y*0 rotate x*63.4333 rotate y*285
texture{T_Wood32}}

I find the object reappears for angles <250 or >320.
Thanks

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