Well, for bioinformatitions the only benefit is that they can calculate 
distances without going into trigonometric functions.
However,  angles even in cartesian PDB system will require trigonometry. 
Fractional coordinates are more difficult, as even distance calculations 
require 
trigonometry and normalisation to cell dimensions :-\. This is all difference, 
no more. And what is nice, that   mathematics takes care of all these 
complications.
BTW, I have no problem with going back to fractional coordinates,  anyhow all 
calculations during refinement are in fractional coordinates  since BDLS or 
even Busing and Levy.
Is it possible to convert PDB coordinate convention to fractional?
 : - )

FF

Dr Felix Frolow   
Professor of Structural Biology and Biotechnology, Department of Molecular 
Microbiology and Biotechnology
Tel Aviv University 69978, Israel

Acta Crystallographica F, co-editor

e-mail: mbfro...@post.tau.ac.il
Tel:  ++972-3640-8723
Fax: ++972-3640-9407
Cellular: 0547 459 608 mathematic

On Jan 6, 2013, at 10:57 , George Sheldrick <gshe...@shelx.uni-ac.gwdg.de> 
wrote:

> Chemical crystallographers have always used fractional coordinates, it makes 
> it so
> much easier to handle symmetry, special positions etc. But if the PDB hadn't
> used orthogonal coordinates, bioinformatics might never have taken off.
> 
> George
> 
> On 01/06/2013 09:34 AM, Eleanor Dodson wrote:
>> 
>> Some of us resisted using an orthogonal format for coordinates, arguing that 
>> the output from a crystal structure should refer to crystal axes. 
>> And since symmetry was a crystal property it was important that we could 
>> "see" it easily.  The PDB format won out,  but I still use coordconv a lot 
>> to turn back the orthogonalised PDB style to fractional coordinates - to see 
>> if this heavy atom solution is the same as that one, given an origin shift, 
>> etc etc. 
>> Eleanor
>> 
>> On 4 Jan 2013, at 20:44, Soisson, Stephen M wrote:
>> 
> 
> -- 
> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry, 
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-22582
> 

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