Treat them as 3-space and look at the sign of the Z-component of the cross product?
Henry Rich > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brian Schott > Sent: Tuesday, August 08, 2006 12:15 PM > To: [email protected] > Subject: [Jgeneral] on you left > > Two objects in 2 dimensional space are facing the > same direction, say D degrees. How does one determine which > object is on the left if the positions of the two objects A > and B in 2D, are given as A and B, for example as follows? > > 'A B' =: 2 1;1 _1 > D =: 90 NB. facing to the East > result: A is on the left > > 'A B' =: _1 0;1 1 > D =: 0 NB. facing to the North > result: A is on the left > > 'A B' =: _1 0;_1 0 > D =: 0 NB. facing to the North > result: A is on the left and on the right (undecided?) > > How does one compute such results? > > (B=) > > Brian Schott > ---------------------------------------------------------------------- > For information about J forums see > http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
