4.48. POWGEN: Powder pattern graphics

Authors: Doug du Boulay

Contact: Doug du Boulay, Crystallography Centre, University of Western Australia, Nedlands 6907, Australia

Warning: This is alpha software!

POWGEN optionally reads a binary pattern archive created with ADDPAT and calculates the expected pattern. These patterns can be viewed and specific factors controlling the calculation manually adjusted to improve fit. The plot range and various graphics rendering attributes can be adjusted and the plots dumped to a plot file for editing or printing. Multiple plots can be generated on one page and multiple pages can be printed.

4.48.1. Overview

POWGEN is a graphical interface program for displaying and manipulating powder diffraction pattern plots. It was designed to permit the user to dump an image of the manipulated page to a .ppp file for previewing with PREVUE or plotting with PLOTX. Multiple pages can be dumped and multiple powder plots can be displayed on one page. The graphical interface was designed exclusively using Tcl/Tk graphics functions, but if desired, the on screen graphics mode can be turned off and a complete description of ONE single page can be specified from the POWGEN control lines. That allows for efficient plotting once a plot format has been designed. In interactive mode the user can manipulate many of the attributes of either, the current graph block, or the layout of the whole page.

Figure 4-3. Screen shot of POWGEN

POWGEN requires as input, either of a .pat file produced by ADDPAT, or a .POT file produced by RIETVD. A check is made for the .POT file first, defaulting to the .PAT file if it exists. If the .PAT file is obtained, it is envisaged that a powder profile could be calculated and manipulated to a certain extent on screen. That requires atom site and hkl data on the input bdf so ADDATM and ADDREF are prerequisites in this mode. Many of the RIETVD commands also apply to POWGEN.

Page layouts can be either rigorously enforced to users specifications, or optimised to fit the page in a number of ways. The page layout is specified via the ARANGE option, where relative graph block positions are specified on a 9x9 grid, with (5,5) defining the location of a one graph block page. Typically EXAMPP will initiate with one graph invoked but with others being added or deleted as the user requires.

4.48.2. File Assignments

4.48.3. Examples

POWGEN pat ho cm 0.5 1.0
:
phase ed  0.00065    :  set the scale factor for this phase
peak  voight 10. 0.5 :  span(in halfwidths) mixing func
hwidth 0.008 0.01 0.0 : 
pasymm  0.0 0.0      : assume symmetric peak
:
block  $2  5 5 :       This block is centered in layout (5 5)    
:                      this block has no numeric label 
:                      So apply these settings to all subsequent blocks
axis x 10 72
axis y -1000 10000
trace obs  1  0.0 0.10 1.0 no $2 1 
trace cal  2  0.0 0.05 1.0 no $2 1 
trace del  3  0.0 0.0 1.0 no $2 1 
:
block 2 5 6 :          This graph block is below previous block
titext This is graph number 2
axis x 10 30 :          plot range 2 theta = 10 to 30 degrees
axis y -1000 6000 :     Intensity range 
axslab x two theta angle
axslab y Intensity (counts per sec) 
trace obs  1  0.0 0.1 1.0 no $2 1  : plot observed
trace cal  2  0.0 0.0 1.0 no $2 1  : plot calculated
trace del  3  0.0 0.2 1.0 no $2 1  : plot difference (delta)
:
:                     If print is requested a .ppp plot file is written
PREVUE ppp
PLOTX xfigl ppp :     produce .fig file for line editing/printing in XFIG
finish