question

Here's the distance calculation for use in the ondrawtrigger - with code to hide the contents if over 20m away.

// If this function returns a true, the default draw code of the object will not be executed.
Vec3 mgroundviewpoint=Vec3(viewpointx(view).value,viewpointy(view).value,viewpointz(view).value);
Vec3 mcurrcentre=current.getLocation(0.5,0.5,0.5).project(current.up,model());
Vec3 groundpath=mgroundviewpoint-mcurrcentre;
double azimuth=-1*viewpointrx(view).value;
double elevation=Math.radians(azimuth);
double viewradius=viewpointradius(view).value;
double groundradius=Math.cos(elevation)*viewradius;
double z=Math.sin(elevation)*viewradius;
double bearing=viewpointrz(view).value-90;
double rotation=Math.radians(bearing);
double y=Math.sin(rotation)*groundradius;
double x=Math.cos(rotation)*groundradius;
Vec3 topov=Vec3(x,y,z);
Vec3 mpov=mgroundviewpoint+topov;
Vec3 path=mpov-mcurrcentre;
 
 
//print("dist:",path.magnitude,"azimuth",azimuth,"groundRadius",groundradius,"height",z,"bearing",bearing,"x",x,"y",y,"flexdistfromview:",distfromviewpoint(current,view));
if (path.magnitude>20)
    switch_hidecontents(current,1);
else
    switch_hidecontents(current,0);

Note the existance of the checkbox for fustrum culling and the FlexSim function distfromviewpoint() which, as the print statement in the code above demonstrates, yields different values (which were often incorrect when I tested it).