IMAGE TOOLS

• Reconstruct image
• Fit PSF
• Extract slit (Cut image)

Reconstruct image

• Principles

  A quantity has been computed for any spectrum in a datacube, and this quantity has been recorded, for each spectrum, into a table. It maybe a line intensity, a line width, a line ratio, and so on... The tool provided here reads this column and the columns holding the coordinates of each spectrum, and constructs the 2D-image of the repartition of this quantity. It is so an straightforward way to obtain intensity, line ratio, velocity, ... maps of the field.
  



• Use

  • Click on [Image] in the main menu, then on [reconstruct image]. The [reconstruct image] window pops up.
  • Enter the table name and the column to be mapped.
  • Click on [Accept]. The result window opens, the image is built, and recorded under the name you gave.



• Parameters

  • Input table : the name of the table from which the numerical data will be extracted to build the image. You can type it in directly, or use the browse icon at the end of the field, or drag and drop it from the Reduction folder.
    
  • Output image : the name of the resultant image. Same possibilities as above...
    
  • Input coordinates columns : the user have to choose among three possibilities :
    
    • CCD [row,column] and the pixel coordinates will be taken automatically from the right columns in the input table, if they exist.
    • Sky [alpha,delta] and the relative alpha,delta will automatically be taken from the right columns in the input table, if they exist. Remember that in the Extract spectra function, the [alpha=0,delta=0] point has been arbitrarily set at the center of the CCD frame, and the coordinate units as arcseconds.
    • Other : if the user checks this option, he is asked to enter the labels of the columns which contain the [X] and [Y] values to be used as coordinates for the image reconstruction.
  • Column to be mapped : this is the label of the column holding the numerical values the user wants to map over the spatial field.
    
  • Image sampling : the user may check the [Auto] button to let the program decide which sampling to use for the reconstructed image. In such a case, the sampling is given by :
    S = min [ (X_max-X_min) / (2 * sqrt(N_x)) , (Y_max-Y_min) / (2 * sqrt(N_y)) ]
    where X_min, X_max, Y_min, and Y_max are the field limits, and N_x, N_y the number of spatial elements in X and Y in the original data. Otherwise, the final image sampling (arc seconds) has to be specified.
    
  • Coordinates limits : if set to [Auto], the image is built over the spatial rectangle which exactly contains the original data. If not, the user is asked to specify the limits to be used; do not trust extrapolation, and avoid larger-than-original images!
    
  • Fill options :
    
    • Adjust center : if the user checks this option, the interpolation grid is adjusted so that there is a [0,0] pixel in the reconstructed image.
      
    • Extrapolate : if the user checks this option, and if there are "holes" in the map, the polynomial surface is locally extrapolated until it fills all the image rectangle.
      
    • Bicubic interpolation : once checked, this constrains the interpolation to be bicubic; default is bilinear.
      
    • Fill triangle : in the interpolation process, a grid of spatial triangles is created over the data. A "mean step" size is computed for this mesh, and the algorithm does not interpolate over triangles much larger than this mean. If the option is checked, the sizes are no more checked, and every region surrounded by three data points is treated. This produces big area differences if original data present some "angled holes", like after a datacube merge (function Mosaic). This option is superseded by the [Extrapolate] one.
      
    • Blank value : this is the value to be used in the reconstructed image if the user did not check [Extrapolate].
      
  • Debug : This switches the program to verbose mode, and more informations are recorded into the history file (see Getting started).
    
  • Save values : All the input values (names, ...) are saved, and become the new default values for this user. They can be recalled at will, and are used each time the [Reconstruct image] window is opened.
    
  • Recall values : The values (names, ...) saved by the user are loaded to the various input fields.
    
  • Default values : The input fields are set to the general defaults values; for instance, the names are set to blank.
    

Fit PSF

• Principles

  A gaussian (or a sum of gaussians), plus a polynomial background, are adjusted on the reconstructed image. The computed gaussian parameters may be taken as an estimate of the actual PSF of OASIS data at the time of the exposure.
  



• Use

  • Click on [Image] in the main menu, then on [Fit PSF]. The [Gaussian PSF fit] window pops up.
  • Enter the name of the image to be fitted, and the number of gaussian components you wish to fit simultaneously.
  • Click on [Accept]. The parameters of the fit are displayed in the result window. A [View result] button allows to display the result. For that, sections of both the gaussian fit (in red) and the underlying image (in black) are overplotted for several radial lines.



• Parameters

  • Input image : the name of the image on which you want to fit a sum of gaussians. You can type it in directly, or use the browse icon at the end of the field, or drag and drop it from the Reduction folder.
  
  
  • Number of gaussians : the user may specify here to fit a single gaussian, or a sum of N gaussians.
  
  
  • Fit window : the user specifies here if the fit should work on the whole frame, or on some restricted area. In this last case, the Center [X,Y] and Size [dX x dY] must be specified; there are default values : center in [0,0], size 2x2 arcseconds.
  
  
  • Save PSF as an image : an image is created from the sum of gaussians + background. The user may specify a name for this new image. There is a default name : dbg_ima.
  
  
  • Output fit table : created automatically, do not care... It holds the radial profiles which are to be used later by the [View result] function. If you are a table collector, you may specify some ad hoc name to keep it.
  
  
  • Max nb of iterations : as one expects...
  
  
  • Tolerance : as one expects...
  
  
  • Debug : This switches the program to verbose mode, and more informations are recorded into the history file (see Getting started).
    
  • Save values : All the input values (names, coordinates, ...) are saved, and become the new default values for this user. They can be recalled at will, and are used each time the [Reconstruct image] window is opened.
    
  • Recall values : The values (names, coordinates, ...) saved by the user are loaded to the various input fields.
    
  • Default values : The input fields are set to the general defaults values; for instance, the names are set to blank.
    

Extract slit (Cut image)

• Principles

  A rectangular aperture (slit) is superimposed over an image. The intensities are summed up across the slit, and the resulting intensity profile along the slit is saved as a 1D file.
  



• Use

  • Click on [Image] in the main menu, then on [Extract slit]. The [Extract slit] window pops up.
  • Enter the name of the Input image you will to cut across. You can type it in directly, or use the browse icon at the end of the field, or drag and drop it from the Reduction folder.
  
  
  • Enter the name of the Ouput spectrum, that is the name of the 1D file recording the cut. Same input possibilities as above.
  • Enter the Center (arc seconds) of the slit, the Width, the Step of the sampling along the slit, the Position angle of the slit.
  • Click on [Accept]. The result is stored as a 1D file. A [View result] button allows to display the "spectrum".



• Parameters

  • Slit length : you may chose to cut across the [Full frame], or to restrict the length of the slit to Length.
  • Subsampling :
  
  
  • Debug : This switches the program to verbose mode, and more informations are recorded into the history file (see Getting started).
    
  • Save values : All the input values (names, coordinates, ...) are saved, and become the new default values for this user. They can be recalled at will, and are used each time the [Reconstruct image] window is opened.
    
  • Recall values : The values (names, coordinates, ...) saved by the user are loaded to the various input fields.
    
  • Default values : The input fields are set to the general defaults values; for instance, the names are set to blank.
    

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