[ Basic Info | References | User Guide ]
Basic Information on imgen
Task: imgen
Purpose: All-purpose image manipulator/creator
Categories: utility, map manipulation
IMGEN is a MIRIAD task which modifies an image, or creates a new
image. See also maths to create images based on expressions involving
X, Y and Z.
Key: in
The input image, which is to be modified. The default is a map
with one plane which consists entirely of zeros.
Key: out
The name of the output image. No default. The output image has the
same characteristics as the input image, if present. If no input
image is given, the `imsize', `cell' and `radec' keywords give the
characteristics of the output.
Key: factor
Factor to multiply the input image by. This is meaningless if no
input image is given. The default is 1.
Key: object
This determines the type of objects added to the input image.
Several objects can be given (the objects can be the same type, or
different), and minimum match is supported. Possible objects are:
level An offset (DC) level.
noise Noise (gaussian distribution).
point A point source.
gaussian An elliptical or circular gaussian.
gauss3 3D elliptical or circular gaussian (for cubes).
disk An elliptical or circular disk.
j1x J1(x)/x function
jet Jet model with power law brightness.
shell 2D projection of an optically-thin spherical shell
comet 2D projection of a parent molecule in comet.
cluster standard isothermal 2D projection for cluster gas.
powerlaw standard power-law model
j0 J0 Bessel function for holography work
Key: spar
Parameters which give the characteristics of the object. The
parameters are given as a sequence of values, with one to six
values needed per object (depending on the object type). When
there are multiple objects, the parameter value for the second
object follow those for the first object, etc. The values are
as follows:
Object Type SPAR values
----------- -----------
level offset
noise rms
point amp,x,y
gaussian amp,x,y,bmaj,bmin,pa
gauss3 amp,x,y,z,bmaj,bmin,pa,bz
disk amp,x,y,bmaj,bmin,pa
j1x amp,x,y,bmaj,bmin,pa
jet amp,x,y,bmaj,bmin,pa
shell amp,x,y,bmaj
comet amp,x,y,scalelength
cluster amp,x,y,core radius
powerlaw amp,x,y,r_1,index1
j0 amp,x,y,r_1
Here offset is the offset level, "rms" is the rms value of
the noise, "amp" is the normally peak value of the object (but
see options=totflux below), "x" and "y" are the offset positions (in
arcsec) of the object relative to the reference pixel, "z" is the
absolute pixel position on the third axis, "bmaj" and "bmin" are the
major and minor axes FWHM (in arcsec), "pa" is the position angle of
the major axis (in degrees), and "bz" is the FWHM (in pixels)
in the 3rd dimension. The position angle is measured from north
towards east.
The default is an object of unit amplitude, at the reference
pixel, with a FWHM of 5 arcsec in x and y and 5 pixels in z.
For powerlaw the scale length defaults to 5 arcsec as well
and the power-law index defaults to 1. For j0, the default
scale length is 5 arcseconds although significant image manipulation
after-the-fact is necessary to make this object useful for holography.
Comet scalelength, and cluster core radius are in arcsec units.
Jet model has brightness with power law index bmaj and bmin along
major and minor axes.
Key: imsize
If not input image is given, then this determines the size, in
pixels, of the output image. Either one or two numbers can be
given. If only one number is given, then the output is square.
For testing purposes a third number can be given to create a cube,
no good coordinate headers however are written for such cubes.
The default is 256 pixels square.
Key: cell
The increment between pixels, in arcseconds. This is only used if
there is no input map. The default is 1 arcsec.
Key: radec
If no input image is given, this gives the RA and DEC of the
image, in hours and degrees, respectively. They can be given in
hh:mm:ss,dd:mm:ss, or as decimal hours and degrees. The default is
RA=0, DEC=30.
Key: options
Extra processing options. Several can be given, separated by
commas. Minimum match is used. Possible values are:
totflux Interpret the "amp" values in the spar keyword as
total integrated flux densities (Normally the "amp"
parameters are interpretted as peak values).
Key: seed
Number used to initialise the random number generator. This is
an integer. Invoking IMGEN with the same value of SEED will give you
identical instance of the noise, whereas a different value will
give you a different instance.