Also by default, the central 2048 x 2048 section of a FITS image is displayed
at bin 1. This default is controlled by the JS9.globalOpts.image object
properties, which can be set in your js9Prefs.js file.
The Bin/Filter/Section plugin allows you to extract sections
from FITS binary tables and images, with options to choose the image
center, image dimensions, and bin factor. For tables, the plugin also
allows you to filter rows of the table by means of arithmetic and
boolean operations on the table columns.
The Bin/Filter/Section plugin works with both FITS representation
files and with ordinary in-memory FITS files. If the displayed FITS
file is a representation file (i.e., it has a parent file, a JS9
helper is connected, etc.), the plugin will ask the JS9 helper to
extract the image section from the parent. Otherwise, it extracts the
section from the in-memory FITS file. This behavior is meant to be
transparent to the user.
When extracting an image section, you can set one or more of the
following options:
For example, if a table has FITS (tlmin, tlmax) dimensions 4096 x 4096, then:
Table filtering allows you to select rows from an FITS binary table
(e.g., an X-ray event list) by checking each row against an expression
involving the columns in the table. When a table is filtered, only
valid rows satisfying these expressions are used to make the image.
A filter expression consists of an arithmetic or logical operation
involving one or more column values from a table. Columns can be
compared to other columns or to numeric constants. Standard JavaScript
math functions can be applied to columns. JavaScript (or C) semantics
are used when constructing expressions, with the usual precedence and
associativity rules holding sway:
NB: when using cfitsio (the default, instead of the deprecated
fitsy.js), table filtering follows cfitsio conventions, which is
documented
here.
Once the desired parameters have been set, pressing the Run
button will filter, bin and display the data.
FITS Image Sections, with Binning and Filtering
The rows in a FITS binary table must be binned before being displayed
as an image. By default, JS9 uses a bin factor of 1 to extract the
central 2048 x 2048 section of the data for display. This default is
controlled by the JS9.globalOpts.table object properties, which can be
set in your js9Prefs.js file.
Specifying 0,0 for the center will cause the section to be extracted from the
center of the image.
Operator Associativity
-------- -------------
() left to right
! (bitwise not) - (unary minus) right to left
* / left to right
+ - left to right
< <= > >= left to right
== != left to right
& (bitwise and) left to right
^ (bitwise exclusive or) left to right
| (bitwise inclusive or) left to right
&& (logical and) left to right
|| (logical or) left to right
= right to left
For example, if energy and pha are columns in a table,
then the following are valid expressions:
pha > 1
energy == pha
pha > 1 && energy ≤ 2
max(pha,energy)≥2.5
Last updated: July 7, 2017