Talk:cansas1d documentation: Difference between revisions
(The Intensity Problem : 3 types of intensity are possible) |
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The "intensity" (see [[cansas1d_SASdata]]) is permitted in three different forms. | The "intensity" (see [[cansas1d_SASdata]]) is permitted in three different forms. | ||
# absolute units: differential cross-section per unit volume per unit solid angle | # absolute units: differential cross-section per unit volume per unit solid angle (typical unit: 1/cm) | ||
# absolute units: differential cross-section per unit atom per unit solid angle | # absolute units: differential cross-section per unit atom per unit solid angle (typical unit: cm^2) | ||
# arbitrary units: usually a ratio of two detectors but ''unit'' is meaningless | # arbitrary units: usually a ratio of two detectors but ''unit'' is meaningless (typical unit: a.u.) | ||
This presents a few problems for analysis software to sort out when reading the data. Fortunately, it is possible to analyze the ''unit'' attribute to decide which type of intensity is being reported and make choices at the time the file is read. '''''But this is an area for consideration and possible improvement.''''' | This presents a few problems for analysis software to sort out when reading the data. Fortunately, it is possible to analyze the ''unit'' attribute to decide which type of intensity is being reported and make choices at the time the file is read. '''''But this is an area for consideration and possible improvement.''''' | ||
Latest revision as of 00:58, 15 November 2008
Problems
The Intensity Problem
The "intensity" (see cansas1d_SASdata) is permitted in three different forms.
- absolute units: differential cross-section per unit volume per unit solid angle (typical unit: 1/cm)
- absolute units: differential cross-section per unit atom per unit solid angle (typical unit: cm^2)
- arbitrary units: usually a ratio of two detectors but unit is meaningless (typical unit: a.u.)
This presents a few problems for analysis software to sort out when reading the data. Fortunately, it is possible to analyze the unit attribute to decide which type of intensity is being reported and make choices at the time the file is read. But this is an area for consideration and possible improvement.
One problem arises with software that automatically converts data into some canonical units used by that software. The software should not convert units between these three types of intensity indiscriminately.
A second problem is that when arbitrary units are used, then the set of possible analytical results is restricted (such as no meaningful volume fraction or number density can be determined directly from <math>I(Q)</math>).
Open topics
How to store results of processing or analysis?
There is no support yet for writing data processing or analysis results back into the canSAS1d/1.0 format. Several details need to be described, including:
- Results should be placed into a SASprocess element
- How should results data be portrayed?
- How to identify the principle axes or parameters?
- How to pass metadata not specifically described?
Some examples already exist in the TRAC repository:
- size distribution: http://svn.smallangles.net/trac/canSAS/browser/1dwg/trunk/bimodal-test1.xml
- undescribed metadata: http://svn.smallangles.net/trac/canSAS/browser/1dwg/trunk/cansas1d.xml
- IgorPro wavenote metadata: http://svn.smallangles.net/trac/canSAS/browser/1dwg/trunk/s81-polyurea.xml
- COLETTE metadata: http://svn.smallangles.net/trac/canSAS/browser/1dwg/trunk/W1W2.XML
