<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META NAME="Generator" CONTENT="MS Exchange Server version 6.5.7651.59"> <TITLE>RE: [Gate-users] difference between /gps/position and /gps/center ?</TITLE> </HEAD> <BODY>  The command /gps/center is for a volume of source. The /gps/position is for single particle. If you want a particle source from one point, you can use /gps/position + /gps/direction to define your particle beam. Otherwise, if you specify a shape of source, you have to use /gps/center to put it into whatever you want position.Then gps will randomly choose position in your defined volume for each particle. Yu Chen, Ph.D. University of Massachusetts Medical School Division of Nuclear Medicine 55 Lake Avenue North Worcester, MA 01655-0243 Phone:  (508) 856-6123 Fax:    (508) 856-4572 -----Original Message----- From: gate-users-bounces@lists.healthgrid.org on behalf of lizhi Sent: Tue 12/4/2007 5:47 AM To: gate-users@lists.healthgrid.org Subject: [Gate-users] difference between /gps/position and /gps/center ? Dear GATER: Would somebody explain me what is the difference between /gps/position and /gps/center ? Examples in gate users guide said using "/gps/centre" to placement a source.  Can I use "/gps/position"? I have check Gate help, it saids: Command directory path : /gate/source/beamsource/gps/ Guidance : General Paricle Source control commands.  The first 9 commands are the same as in G4ParticleGun  Sub-directories :  Commands :  1) List * List available particles.  2) particle * Set particle to be generated.  3) direction * Set momentum direction.  4) energy * Set kinetic energy.  5) position * Set starting position of the particle.  6) ion * Set properties of ion to be generated.  7) time * Set initial time of the particle.  8) polarization * Set polarization.  9) number * Set number of particles to be generated.  10) type * Sets source distribution type.  11) shape * Sets source shape type.  12) positronRange * Sets positron range.  13) centre * Set centre coordinates of source. ......... But I did not understand the difference. Thank you for anyone explain me it. Kind Regards Zhi LI VUB _______________________________________________ Gate-users mailing list Gate-users@lists.healthgrid.org <A HREF="http://lists.healthgrid.org/mailman/listinfo/gate-users">http://lists.healthgrid.org/mailman/listinfo/gate-users</A> </BODY> </HTML>