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| − | <pre>
| + | {{imfit}} |
| − | Help on imfit task:
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| − | Fit one or more elliptical Gaussian components on an image region(s)
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| − | PARAMETER SUMMARY
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| − | imagename Name of the input image
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| − | box One or more box regions to use for fitting,
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| − | eg "100, 120, 200, 220, 300, 300, 400, 400"
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| − | to use two boxes. If both box and region
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| − | parameters are specified, box is used.
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| − | region Region name or region specified using rg tool.
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| − | A region from another image can be specified using the
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| − | imagename:regionname syntax, eg "mycontinuumimage:mysourceregion"
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| − | chan Spectral channel on which to perform fit (only one may be specified).
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| − | stokes Stokes parameter to fit.
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| − | mask Mask to be applied to the image. Can be a mask associated with the
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| − | image or an LEL expression.
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| − | includepix Range of pixel values to include for fitting. Array of two numeric
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| − | values assumed to have same units as image pixel values. Only one
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| − | of includepix or excludepix can be specified.
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| − | excludepix Range of pixel values to exclude for fitting. Array of two numeric
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| − | values assumed to have same units as image pixel values. Only one
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| − | of includepix or excludepix can be specified.
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| − | residual Name of the residual image to write.
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| − | model Name of the model image to write.
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| − | estimates Name of file containing initial estimates of component parameters
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| − | (see below for formatting details).
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| − | logfile Name of file to write fit results.
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| − | append If logfile exists, append to it (True) or overwrite it (False).
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| − | newestimates File to write fit results which can be used as initial estimates
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| − | for next run.
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| − | OVERVIEW
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| − | Imfit is used to fit one or more gaussians to sources in an image.
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| − | Fitting is limited to a single spectral channel and a single polarization.
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| − | If the image has a clean beam, the task will report both the convolved
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| − | and the deconvolved fit results.
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| − | The task returns a dictionary with two keys, 'converged' and 'results'.
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| − | The value of 'converged' is a boolean which indicates if the fit converged.
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| − | The value of 'results' is a component list reflecting the fit results. In the
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| − | case of a clean image, the results are the convolved results.
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| − | The region can either be specified by a box (blc,trc) or a region (if both
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| − | are given, the box is used). Ranges of pixel values can be included or
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| − | excluded from the fit.
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| − | If specified, the task will write the residual and/or model images for
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| − | successful fits.
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| − | If an estimates file is not specified, the task will attempt to estimate
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| − | initial parameters and fit a single Gaussian. If a multiple Gaussian fit
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| − | is desired, the user must specify initial estimates via a text file
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| − | (see below for details).
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| − | The user has the option of writing the result of the fit to a log file,
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| − | and has the option of either appending to or overwriting an existing file.
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| − | | |
| − | The user has the option of writing the (convolved) parameters of a successful
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| − | fit to a file which can be fed back to imfit as the estimates file for a
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| − | subsequent run.
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| − | MASK SPECIFICATION
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| − | Mask specification can be done using an LEL expression. For example
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| − | mask = '"myimage">5' will use only pixels with values greater than 5.
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| − | INCLUDING AND EXCLUDING PIXELS
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| − | Pixels can be included or excluded from the fit based on their values
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| − | using these parameters. Note that specifying both is not permitted and
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| − | will cause an error. If specified, both take an array of two numeric
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| − | values.
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| − | ESTIMATES
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| − | Initial estimates of fit parameters may be specified via an estimates
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| − | text file. Each line of this file should contain a set of parameters for
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| − | a single gaussian. Optionally, some of these parameters can be fixed during
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| − | the fit. The format of each line is
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| − | peak intensity, peak x-pixel value, peak y-pixel value, major axis, minor axis, position angle, fixed
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| − | | |
| − | The fixed parameter is optional. The peak intensity is assumed to be in the
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| − | same units as the image pixel values (eg Jy/beam). The peak coordinates are specified
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| − | by pixel values. The major and minor axes and the position angle are the convolved
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| − | parameters if the image has been convolved with a clean beam and are specified as quantities.
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| − | The fixed parameter is optional and is a string. It may contain any combination of the
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| − | following characters 'f' (peak intensity), 'x' (peak x position), 'y' (peak y position),
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| − | 'a' (major axis), 'b' (minor axis), 'p' (position angle).
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| − | | |
| − | In addition, lines in the file starting with a "#" are considered comments.
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| − | | |
| − | An example of such a file is:
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| − | # peak intensity must be in map units
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| − | 120, 150, 110, 23.5arcsec, 18.9arcsec, 120deg
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| − | 90, 60, 200, 46arcsec, 23arcsec, 140deg, fxp
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| − | | |
| − | This is a file which specifies that two gaussians are to be simultaneously fit,
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| − | and for the second gaussian the specified peak intensity, x position, and position angle
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| − | are to be held fixed during the fit.
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| − | | |
| − | EXAMPLE:
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| − | Here is how one might fit two gaussians to multiple channels of a cube using the fit
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| − | from the previous channel as the initial estimate for the next. It also illustrates
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| − | how one can specify a region in the associated continuum image as the region to use
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| − | as the fit for the channel.
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| − | imagename = "co_cube.im"
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| − | # specify region using region from continuum
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| − | region = "continuum.im:source.rgn"
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| − | chan = 2
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| − | # only use pixels with positive values in the fit
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| − | excludepix = [-1e10,0]
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| − | # estimates file contains initial parameters for two Gaussians in channel 2
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| − | estimates = "initial_estimates.txt"
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| − | logfile = "co_fit.log"
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| − | # append results to the log file for all the channels
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| − | append = "True"
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| − | # write file to use as estimates for next channel
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| − | newestimates = "estimates3.txt"
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| − | imfit
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| − | # now loop through channels
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| − | for x in range(3,20):
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| − | chan = x
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| − | # feed initial estimates using results of last fit
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| − | estimates = "estimates" + str(x) + ".txt"
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| − | newestimates = "estimates" + str(x + 1) + ".txt"
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| − | imfit
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| − | </pre>
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