<div class="gmail_quote">On Mon, Mar 8, 2010 at 10:04 AM, David Gobbi <span dir="ltr"><<a href="mailto:david.gobbi@gmail.com">david.gobbi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Hi Rakesh,<br>
<br>
It is used in cases where you have one vector, and need to find an<br>
arbitrary vector that is perpendicular to it.<br>
<br>
The idea behind this is that when you have one vector, there are an<br>
infinite number of vectors that are perpendicular that vector, so you<br>
need to supply an additional constraint (the angle "theta") to specify<br>
which perpendicular vector you want.<br>
<br>
This is in contrast to the case where you have two vectors and need to<br>
find a third that is perpendicular to the first two, in which case you<br>
can just use a cross product.<br>
<br>
David<br>
<div><div></div><div class="h5"></div></div></blockquote></div><br><div>I have nothing to add, David G's explanation was perfect, but here is a demonstration:</div><div><a href="http://www.vtk.org/Wiki/VTK/Examples/PerpendicularVector">http://www.vtk.org/Wiki/VTK/Examples/PerpendicularVector</a></div>
<div><br clear="all">Thanks,<br><br>David</div>