>> >In vernacular the solid cone is a teepee: D is >> >its base; A is its peak; C is the fire in the >> >center of the base; the axis is the smoke rising; >> >and theta is the angle between the smoke rising >> >and one of the support poles from the edge of the >> >base to the peak. >> > > ><snip> > >Ashley , can you clarify which of the following corresponds to your problem? > >[1] As used by Laurent, a finite teepee bounded by its base? > In this case do you have to worry about the other finite teepee on the >other side of the peak being included? > >[2] A single infinite cone containing (0, 0,0), which is how I interpreted >your initial definition? > >[3] Two infinite cones, one on each side of the peak A. > >In either of the latter two cases you only need to calculate phi, not any >distances. > >Thanks, > >Cheers, Peter It is [1]. Since I am dealing with a satellite and what it can see on the ground (known as it's footprint) it depends upon what side of the earth it and the satellite are on, ie it's no good if the satellite is over the artic and it tells me that the station in the antarctic can recieve the signal, just because it happens to be directly opposite. Here is a clearer explanation, I hope. The satallite, located at (sX#,sY#,sZ#) in the XYZ (3D) Plane, centered at the center of the earth such that the X axis comes out at the equator in the 0th degree of longitude and the Y axis comes out at the equator 90 degrees further around and the Z axis emerges from the north pole. A groundstation located at (lX#,lY#,lZ#) wants to know if it will be in range to recieve data from the satellite that can transmit in what appears as a cone, ie it would appear as like and upside down ice-cream cone where the tip of the cone is at the satellite and the rim of the cone sits on the surface of the earth such that the central axis of the cone is perpendicular to the tangents at the surface of the sphere of earth ie if you connected the tip of the cone with the center of it's base then the line would extend through the origin (0,0,0). If that needs some explaining try thinking about a basketball where the valve is the Z axis and one of the seams forms the 0th degree of longitude (hopefully there is one for the equator as well) and then think of an ice-cream cone sitting on the ball such that it would be perpendicular to the tangent at the surface or altenativley make a cone with a segment of a circle of paper to play around with. Then suppose there is a dot on the surface of the ball that you want to determine if it's in the cone (mathematically not visually). I hope that makes it clearer without confusing it anymore, Thanks for the help, Regards, Ashley ~)~ ============================================================= Ashley Butterworth Email: macbse@... ============================================================= _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com