Visualizing SED Data in Iris

Contents

• Introduction
• Setting Display Preferences
  • Adjusting the Coordinates View Port
  • Refreshing the Data Plot
  • Units
  • Axis Scale
  • Grid
  • Plot Legend
  • Change SED Display Name
• Displaying Metadata and Data Values
  • Data tab
  • Point Metadata tab
  • Segment Metadata tab
• Selecting and Masking SED Data Points
  • Select Points using Metadata Browser
  • Select Points from Data Plot
  • Select Points by Boolean operations
• Extracting a Filtered SED
• Co-plotting Separate SEDs
• Saving Plot Image to File
• Iris Interoperability with other Virtual Observatory Applications
• History

Adjusting the coordinates view port

The set of widgets in the Visualizer toolbar are available for adjusting the view and orientation of the SED segment(s) within the main display.

Resetting the Data Plot

The “Reset” button is available within the Iris main display for resetting the data plot so that all edges. |

Units

The preferred units for the data display, e.g., “ergs/cm2/s/angstrom” versus “angstrom”, may be set using either the “Units” button in the upper-right corner of the main display. This also updates the units shown in the Metadata Browser’s “Data” tab.

The “Units” button allows you to choose the spectral and flux/flux density units to display an SED in. A dialog box populated with all available physical units will pop up: the left column is for the spectral (X) axis, and the right column holds the flux/flux density axis. Selecting the desired units and clicking the “Update” button adjusts the data display to the desired preference.

Axis Scale

The X and Y axes can be plotted in linear or logarithmic scales. The user controls the scaling by clicking “View –> Plot Type –>” on the menu bar, then choosing the scaling.

• Log - plot both X and Y in a logarithmic scale.
• Linear - plot both X and Y in a linear scale.
• X Log - plot X in a logarithmic scale, and Y linearly.
• Y Log - plot Y in a logarithmic scale, and X linearly.

Grid

Selecting the “Grid” option in the main display overlays a coordinate grid onto the main plot.

Plot legend

Be default, a plot legend is shown in the top-right corner of the plot display. The legend can be hidden/shown by checking the preference “View –> ”Show Legend" off and on.

Change SED Display Name

By default, the SED Viewer window displays either “Sed” or “Iris Visualizer” for any file loaded into Iris. This name can be changed in the SED Builder window. Type the desired name in the bar next to “ID:” under “Selected SED” then click “Change.” From now on, the SED Viewer window will display the new name on the top bar and on the plot.

Data tab

The X and Y coordinate values of each SED data point in the Iris display are contained in the “Spectral Axis” and “Flux Axis” columns of the Data tab, and reflect the values that are currently plotted in the Iris display; when the plot units are changed, the Data tab updates accordingly.

Point Metadata tab

When available, the Metadata tab includes many useful pieces of information about the data points currently displayed. When a SED is imported from NED, as in the example considered in this thread, the metadata includes such things as the bibliographic reference code for each data point, the spectral range covered by instrument used to obtain data point, data point uncertainty and flux values as they are published, data point significance values, among other properties. The full list of metadata information available for each data point will depend on the specific data sources.

Segment Metadata tab

Metadata that is common to all data points in a SED segment is displayed under this tab, in a similar table as the one that appears under the Point Metadata tab.

Selecting Points using Metadata Browser

Data points can be masked from the Iris plot display and fitting sessions with a number of methods.

The most basic works by simply selecting the rows corresponding to these points in any one of the Point Metadata or Data tabs of the Metadata window, and then clicking “Mask Points” at the bottom of that window. You can select the points by clicking the desired rows while pressing the Ctrl/Command key. In the display, the selected points will be removed.

In the Metadata Browser, masked points are denoted by a checkmark in the “Masked” column. The “Masked” column is only present when at least one point is masked. Note that this checkbox column is not clickable; to mask/unmask points, select the rows you wish to edit, then click or .

The Data and Point Metadata tables can be hierarchically sorted by clicking on specific column headers. Clicking once sorts the rows in ascending order of that column; the next click sorts it in descending order . Using that mechanism, rows can be re-ordered together according to relatively complex selection criteria against column content. This facilitates the lumping together of the desired rows, that can in turn be selected and operated upon with the tools described in the preceding paragraph.

For example, we can click on the “DataComments” column and easily mask data points with values “Recalibrated Data” by holding down the Shift key and clicking the top and bottom of the “Recalibrated Data” block in the table (see figure below).

Note that columns can be re-positioned at will by dragging their headers horizontally.

Also note that string-valued columns are treated in lexical order. Integer and floating-point-valued columns are treated in numerical order.

Select Points from Data Plot

Data point selection can also be performed based on the plot itself, instead of the table. One way to do that is by clicking on a specific data point on the display. The corresponding row in both the Point Metadata and Data tables will be selected. This selection is non-destructive, meaning that by successively clicking on points on the display, one can add the rows corresponding to each one, to the set of selected rows.

Select Points by Boolean operations

In order to enable even more complex selection criteria though, table rows can be selected based on the result of an arbitrary Boolean expression computed on selected column contents. This expression is entered in the ‘Filter Expression’ text field, and by hitting Return, or clicking on the ‘Select points’ button, the expression is computed for every row in the table, and the row is selected if the Boolean result is True.

In the expression, columns are referred by their ordering, where the first column is 0. Columns are specified by a “$” followed by the column number. For example, given the table below, one may select the points which have an associated uncertainty with

$4 > 0

then they can mask the points without associated errors by clicking “Invert Selection”.

Columns may be arbitrarily combined in an expression; what is required are boolean comparisons with at least one column on the left- or right-hand side. Comparisons may be combined with the logical operators AND, OR, and NOT. Expressions are evaluated following the basic order of operations. Iris uses javaluator under the hood as to evaluate numeric expressions. All mathematical operators (*, /, +, -,^,log(),log10()) allowed in javaluator may be used in the filter expression.

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Here is an example of a more complex filter expression:

$3 <= $1 * ($2 + 2.0 * $4) AND $4 > 0

This means “select points where the values in column 3 are less than or equal to the values of (column 2 plus 2 times column 4), all times column 1. Out of these selected points, only pick those whose values in column 4 are greater than 0”.

Caveat: Only numeric columns may be filtered in Iris 3.0.

WARNING: Currently columns may only be specified by their column order. If a user applies a mask to come data points, the new column will push the columns over by 1, so that one must add 1 to their column specifiers in the filter expression. The same applies for a user re-ordering the columns; if the

For example, if the column expression is

$2 > 1.5 * $3

and the user moves the third column to the place of the second column, $2 refers to the current 2nd column, which was previously column 3.

(See more examples of using the Boolean filter in Co-plotting Separate SEDs)

Metadata Browser Example with Co-plotted SEDs

In this example, we use the same NED SEDs “M82” and “NGC7714” from above.

In co-plot mode, the Metadata Browser orders the rows by SED first, then by spectral value. This is true for both the Data and Point Metadata tabs. The same filtering, masking, and selection capabilities are available in co-plot mode.

To restore the original row ordering of the co-plotted table, click on the “Index” column in either tab.

Let’s say we’re interested in points with published uncertainties and with flux values larger than 1.0 Jy. We can mask out the other points from the plot and the Fitting Tool. Click on the “Data” tab and type $2 > 1.0 AND $4 > 0 into the Filter Expression field, where $2 is the Flux_Value column, in Jy, and $4 is Flux_Error. We then click “Select Points” –> “Invert Selection” –> “Mask Points”.

One can “Extract” the desired points to a new SED. If you masked the points in the example above, you can either

• “Clear All” the masked points, type in the filter expression $2 > 1.0 AND $4 > 0, click “Select Points”, then “Extract”

or

• sort the Masked column, click the first unmasked point, hold the Shift key, and select the last unmasked point, then click “Extract.” An image of this method is shown below:

Either method will produce new SED called “FilterSed.” This SED is displayed in the Viewer, and is available for saving, appending and analyzing from the SED Builder window. The final SED is displayed in the figure below.