Date: Fri, 03 May 2002 16:41:57 
Newsgroup: sci.techniques.xtallography 
Subject: Re: International Tables Diagrams
From: Mike Glazer [[email protected]]
At: Oxford University, England

There are two answers to this as far as I can see:
1. If they put the origin somewhere else then you would legitimately write
and ask why there? It's there because it's there!

2. It is convenient to use the top left corner because with a right-handed
choice of axes one has a down the page, b to the right and c out of the
page. Thus by putting the origin at the top left we have the three positive
axes a b and c coming from this origin across and down the page.

Mike Glazer
Oxford

Date: Fri, 03 May 2002 19:37:48
Newsgroup: sci.techniques.xtallography 
Subject: Re: International Tables Diagrams
From: James Silverton [[email protected]]

Mike Glazer wrote:
>
> There are two answers to this as far as I can see:
> 1. If they put the origin somewhere else then you would legitimately write
> and ask why there? It's there because it's there!

> 2. It is convenient to use the top left corner because with a right-handed
> choice of axes one has a down the page, b to the right and c out of the
> page. Thus by putting the origin at the top left we have the three positive
> axes a b and c coming from this origin across and down the page.
>
> Mike Glazer
> Oxford
>
> "James Silverton"  wrote in message
> news:[email protected]...

> > Someone just asked me why the space group diagrams in the Tables have
> > the origin at the top left corner of the page. I have a vague feeling
> > that someone once told me but I cannot remember. Does anyone know?

Thanks for the reply Mike. Of course, ultimately the question is
unimportant apart from historical interest but I have never accepted
"because it is" as an answer :-).

However, the original questioner felt that the system was contrary to
the normal way of drawing a graph with the origin at the lower left. I'm
afraid that I don't see the arguments about convenience since the origin
could be placed at the lower left with a 90 degree rotation of the
picture without doing violence to the handedness. I don't have a copy of
Kathleen Lonsdale's first version of the Tables but was it perhaps her
choice? By no means all books on crystallography follow the Tables.

Best wishes,

Jim.
--
James V. Silverton
Potomac, Maryland.

Subject:  Re: International Tables Diagrams
Date: Mon, 6 May 2002 10:16:16 +0100
From: "Mike Glazer" [[email protected]]
Organization: Oxford University, England
Newsgroups: sci.techniques.xtallography

The structure factor tables of Kathleen Lonsdale were without diagrams. She
does mention in her introduction that choices of origins etc were made by
Wyckoff and are also given in the Internationale Tabellen Vol 1. 1935. In
this latter volume (which I also have) the chapter on space groups is by
Astbury, Mauguin, Hermann, Niggli, Brandenberger and Lonsdale (ne Yardley).
In the introduction they describe the current choice of origin as being in
the top left.  They also say "The representation rests principally on
Schiebold's atlas (which I do not have!) along with certain modifications
linking up with those due to Astbury and Yardley(Lonsdale)." The earlier
tables of Astbury and Yardley were published  in Phil. Trans. Roy. Soc, A224
(1924) but I have not had time to go and read this.

By the way, funnily enough the standard choice of origin for graphics in
computer screens is at the top left too!

Mike Glazer
Oxford

Subject: Re: International Tables Diagrams
Date: Mon, 6 May 2002 12:55:16 +0100
From: Harry Powell [[email protected]]
Organization: University of Cambridge, England
Newsgroups: sci.techniques.xtallography

Hi

Two other commonly encountered places where the top left is the origin
chosen are books (and other printed organs) using the Latin and Cyrillic
alphabets and the raster for VDUs (e.g. television, comuter
displays...). 

You're probably reading this using an application that sets the origin at
the top left...
 
> By the way, funnily enough the standard choice of origin for graphics in
> computer screens is at the top left too!

Harry
-- 
Dr Harry Powell, MRC Laboratory of Molecular Biology,
MRC Centre, Hills Road, Cambridge, CB2 2QH

See http://www.mrc-lmb.cam.ac.uk/harry  for Mosflm, BCA and
crystal growing details