CASA Region Format

Overview

Region files have two different kinds of definitions, "regions" and "annotations", each of which is one line long. To indicate an annotation, a line must begin with "ann".  Lines that begin with the comment character (#) are not considered for processing or display.  

The first line of a file may define global parameters that are to be used for all regions and annotations in that file, in which case the line starts with the word "global". The parameters set here may also be overridden by keywords in a specific line, in which case the keywords pertain only to that one line.  

• Regions: all regions are considered by tasks.  They will be displayed by visualization tasks as well as used to create masks, etc., as appropriate.

• Annotations: these are used by display tasks, and are for visual reference only.

Region definitions

All regions lines will follow this general arrangement:

{shape} {additional parameter=value pairs}

The possible parameter/value pairs are described in more detail below.  Note that most parameters beyond the shape and its coordinates can be defined globally.

Possible units for coordinates are:

• sexagesimal, e.g. 18h12m24s for right ascension or -03.47.27.1 for declination
• decimal degrees, e.g. 140.0342deg for both RA and Dec
• pixels, e.g. 204pix

Possible units of length are:

• degrees, e.g. 23deg
• arcminutes, e.g. 23arcmin
• arcseconds, e.g. 23arcsec
• pixels, e.g. 23pix

Units must always be included when defining a region.

Allowed shapes

• Rectangular box; the two coordinates are two opposite corners:

box[[x1, y1], [x2, y2]]

• Center box; [x, y] define the center point of the box and [x_width, y_width] the width of the sides:

centerbox[[x, y], [x_width, y_width]]

• Rotated box; [x, y] define the center point of the box; [x_width, y_width] the width of the sides; rotang the rotation angle:

rotbox[[x, y], [x_width, y_width], rotang]

• Polygon; there could be many [x, y] corners; note that the last point

will connect with the first point to close the polygon:

poly[[x1, y1], [x2, y2], [x3, y3], ...]

• Circle; center of the circle [x,y], r is the radius:

circle[[x, y], r]

• Annulus; center of the circle is [x, y], [r1, r2] are inner and outer radii:

annulus[[x, y], [r1, r2]]

• Ellipse; center of the ellipse is [x, y]; semi-major and semi-minor axes are [bmaj, bmin]; position angle of the major axis is pa:

ellipse[[x, y], [bmaj, bmin], pa]

Annotation definitions

In addition to the definitions for regions [above], the following are always treated as annotations:

• Line; coordinates define the end points of the line:

line[[x1, y1], [x2, y2]]

• Vector; coordinates define end points; second coordinate pair is location of tip of arrow:

vector[[x1, y1], [x2, y2]]

• Text; coordinates define leftmost point of text string:

text[[x, y], 'my text']

• Symbol; coordinates define location of symbol (see [Appendix A] for a list of allowed symbols):

symbol[[x, y], {symbol}]

Global definitions

Definitions to be used throughout the region file are placed on a line beginning with 'global', usually at the top of the file.  These definitions may also be used on any individual region or annotation line; in this case, the value defined on that line will override the predefined global (but only for that line).  If a 'global' line occurs later in the file, subsequent lines will obey those definitions.

Coordinate reference frame:

• Possible values: J2000, JMEAN, JTRUE, APP, B1950, B1950_VLA, BMEAN, BTRUE, GALACTIC, HADEC, AZEL, AZELSW, AZELNE, AZELGEO, AZELSWGEO, AZELNEGEO, JNAT, ECLIPTIC, MECLIPTIC, TECLIPTIC, SUPERGAL, ITRF, TOPO, ICRS

• Default: image value

coord = J2000

Frequency/velocity axis:

• Possible values: REST, LSRK, LSRD, BARY, GEO, TOPO, GALACTO, LGROUP, CMB
• Default: image value

frame=TOPO

Frequency/velocity range:

range=[min, max]

• Possible units: GHz, MHz, kHz, km/s, Hz, channel
• Default: image range

Correlation axis:

corr=[X, Y]

• Possible values: I, Q, U, V, RR, RL, LR, LL, XX, XY, YX, YY, RX, RY, LX, LY, XR, XL, YR, YL, PP, PQ, QP, QQ, RCircular, LCircular, Linear, Ptotal, Plinear, PFtotal, PFlinear, Pangle
• Default: all planes present in image

Velocity calculation:

veltype=RADIO  

• Possible values: RADIO, OPTICAL, Z, BETA, GAMMA
• Default: image value

Rest frequency:

restfreq=1.42GHz

• Default: image value

Line characteristics:

linewidth=1
linestyle='-'

• Possible values: any line style recognized by matplotlib: '-'=solid, '--'=dashed, '-.'=dot-dashed, ':'=dotted
• Default: linewidth=1, linestyle='-'

Symbol characteristics:

symsize = 1 
symthick = 1

Region, symbol, and text color:

color=red

• Possible values: any color recognized by matplotlib, including hex values
• Default: color=green

Text font characteristics:

font=Helvetica 
fontsize=10pt 
fontstyle=bold
usetex=True/False

• Possible values: those available in matplotlib. The 'usetex' is a boolean parameter that determines whether or not the text line should be interpreted as LaTeX, and would require working LaTeX, dvipng, and Ghostscript installations (equivalent to the text.usetex parameter in matplotlib).

Allowed additional parameters

These must be defined per region line:

Labels: label='string'   # text label for a region; should be placed so text does not overlap with region boundary

"OR/NOT" operators: A "+" at the beginning of a line will flag it with a boolean "OR" (default), and a "-" will flag it with a boolean "NOT". Overlapping regions will be treated according to their sequence in the file; i.e., ((((entireImage OR line1) OR line2) NOT line3) OR line4). This allows some flexibility in building "non-standard" regions. Note that a task (e.g., clean) will still consider all lines: if one wishes to remove a region from consideration, it should be commented out ("#"). Default: OR (+)

Examples

A file with both global definitions and per-line definitions:

global coord=B1950_VLA, frame=BARY, corr=[I, Q], color=blue

# A simple circle region:
circle[[18h12m24s, -23d11m00s], 2.3arcsec]

# A box region, this one only for annotation:
ann box[[140.0342deg, -12.34243deg], [140.0360deg, -12.34320deg]]

# A rotated box region, for a particular range of velocities:
rotbox[[12h01m34.1s, 12d23m33s], [3arcmin, 1arcmin], 12deg], range=[-1240km/s, 1240km/s]

# An annular region, overriding some of the global defaults:
annulus[[17h51m03.2s, -45d17m50s], [0.10deg, 4.12deg]], corr=[I,Q,U,V], color=red, label='My label here'

# Cuts an ellipse out of the previous regions, but only for Q and a particular frequency range:
-ellipse[[17:51:03.2, -45.17.50], [0.25deg, 1.34deg], 45rad], range=[1.420GHz, 1.421GHz], corr=[Q], color=green, label='Removed this'

# A diamond marker, in J2000 coordinates:
symbol[[32.1423deg, 12.1412deg], D], linewidth=2, coord=J2000, symsize=2