VMT Overview

The VMT GUI layout is made up of Control Panels and Displays. The Control Panels on the right and left side of the GUI allow the user to specify the interferometer, baseline, target to be simulated, observables to be displayed, and the time cadence of the simulation. The display in the center of the GUI allow the user to view the predicted simulated observables (both in graphical and textual formats), summary information about the target and instrument being simulated, and to customize the control panels to the user's preference.

1. The control panels are made up of the following sub control panels:

     ¥  Mode Selection Panel

     ¥  Site/Baseline Selection Panel

     ¥  Target Model Parameters Panel

     ¥  Target Model Components Panel ("Analytical Models" mode only)

     ¥  Single Component Parameters Panel ("Analytical Models" mode only)

     ¥  Image Upload Parameter Panel ("Image Upload" mode only)

     ¥  Image upload button and image display ("Image Upload" mode only)

     ¥  Plot Content Selection Panel

     ¥  Instrument Parameter Panel

     ¥  Wavelength Parameter Panel

     ¥  Observing Parameter Panel

2. The display panels are made up the following tabs:

     ¥  Observing Parameter Panel

     ¥  Plot Tab

     ¥  Simulated Data Tab

     ¥  Model Tab ("Analytical Models" mode only)

     ¥  Instrument Tab

     ¥  FITS Image (only if FITS image has been uploaded)

     ¥  Image Tab

     ¥  2D Vis Modulus Tab

     ¥  Nuller Response Tab (for KI only)

     ¥  OI-FITS Data (only is OI-FITS data has been loaded)

Each of the sub panels and display tabs are described in further detail in subsequent sections.

Starting the VMT

In order to begin using the VMT, a target model must first be created (or read in from a .vmt disk file if previously created and saved to disk, or uploaded from a FITS file containing a brightness image). The default behavior for the VMT is to come up in Analytical Model Mode. The observables are immediately displayed in the center plot tab based upon the initial default settings of the control panels. Upon modification of various parameters within the control panels, the resident model is immediately recalculated and it observables displayed. The functionality of these control panels are described in the subsequent sections.

File Pulldown Menu

The VMT File Pulldown Menu allows the user to restore a previous VMT session by loading in a VMT session file (VMT session files have a .vmt extension), save the current VMT sessions, save the predicted simulation data to a file, read an OI-FITS file to overlay the current simulated data and exit the VMT application.

When finished with a session, the user has the option of saving the session by selecting File->Save VMT Session File from the menu bar. This option prompts the user for a name and location to save the session file, which is an ascii file with a .vmt extension. Once saved, the user can subsequently load the file back in (File->Read VMT Session File) recreating the session in a later session without having to re-enter all the information.

Mode Selection Panel

The user can establish a target model by either selecting "Analytical Model", or "Upload Image" in the "Mode Selection Panel".

In the "Analytical Model" mode, the VMT provides the "Single Component Parameter" panel, which supports the creation of the single component brightness models (point source, uniform disk, Gaussian or uniform disk) as well as the "Target Model Component Parameter" panel which allows the creation of linear combinations of these elementary components. Upon starting up the VMT, a default (initially a uniform disc but can be changed) target is selected, with parameters initialized to zero. The user can then modify these values via the Single Component Parameters panel, select a different component from the Target Type pull-down menu, or construct a composite model using the "Add" and "Delete" buttons in the Target Model Components Panel. In the case of a composite model, the observables plotted correspond to the currently highlighted component in the list or to the global model, via plotting controls described later in this manual.

In the "Upload Image" mode, the VMT displays the "Upload Image" panel. This panel supports the uploading of arbitrary brightness models from a FITS formatted file specifying an image of the object of interest and a specification of the image pixel scale (i.e. milli-arcsec/pixel). The VMT does not attempt to read the pixel scale or image orientation from the input FITS file. This panel is further described in the following sections.

Site/Baseline Selection Panel

The Site/Baseline Selection panel allows the user to select an interferometer location and it's associated baseline(s). The currently supported interferometers are KECK, PTI, NPOI, CHARA, VLTI and SUSI.

Upon selection of an interferometer, all associated baselines are displayed in the "Baseline(s)" list. The first baseline in the list is selected as the default. The user can select any baseline in the list, a contiguous subset of baselines, or all the baselines by clicking on any baseline, holding down the Shift key and selecting another baseline. Each baseline can be toggled to be displayed or hidden by holding down the Control key and clicking. All selected baselines are be plotted simultaneously on the "Plot" tab in the center display panel.

NOTE: Nulling observables are only enabled and calculated for the Keck Interferometer.

Target Model Parameter Panel

The Target Model Parameter panel allows the user to specify parameters that apply to the composite model as a whole, i.e. the phase center declination only at this time.

Single Component Parameter Panel

The Single Component Parameter Panel enables the user to enter/modify parameters for each target type. The user can select one of the morphologies using the "Target Type" pull-down menu. The panel will configure itself to allow the user to enter/modify the relevant parameter values specific to that morphology.

The tool currently supports four morphologies: Point Source, Uniform Disc, Gaussian, and Uniform Ring. 

Parameters common to all of the component morphologies are:

* Name specifies the name of the model component and can be any string of up to 20 characters

* RA Offset specifies the component's Right Ascension offset with respect to the phase center (milliarcseconds)

* Dec Offset specifies the component's Declination offset with respect to the phase center (milliarcseconds)

* Flux Fraction specifies the component's fractional contribution to the total flux (total composite flux must be less than or equal to 1.0).

The non-point source morphologies (i.e. Uniform Disk, Gaussian, and Uniform Ring) contain additional parameters describing their size and shape:

For Uniform Disk and Gaussian:

* Major Axis Diameter specifies the angular diameter of the major axis (milliarcseconds)

* Minor Axis Diameter specifies the angular diameter of the minor axis (milliarcseconds). Different than the major axis diameter for elliptical morphologies.

* Major Axis Position Angle specifies the orientation of the elliptical brightness distribution, via the position angle of the major axis, measured East of North (degrees)

For Uniform Ring:

* Major Axis Inner Diameter specifies the ring inner angular diameter along the major axis (milliarcseconds)

* Major Axis Outer Diameter specifies the ring outer angular diameter along the major axis (milliarcseconds)

* Minor Axis Outer Diameter specifies the inner ring angular diameter along the minor axis (milliarcseconds). Different than the major axis outer diameter for elliptical morphologies.

* Major Axis Position Angle specifies the orientation of the elliptical brightness distribution, via the position angle of the major axis, measured East of North (degrees)

The "Reset" button allows the user to cancel all the modified target parameters of the selected target and revert all parameters to the values they were in upon initially selecting the target for modification (or in the case of adding a target, to the original default values).

Target Model Components Panel

The Target Model Component Panel lists all of the components currently defining a composite. It also tracks the total fractional flux, and assigns any remaining flux as a completely incoherent component. The component that is highlighted is the one displayed in the "Single Component Parameters" panel and can be modified simply by changing any of the values. The changes are immediately saved and reflected in the data output and plots.

To delete a target in the model, select it from the Target Component Model list and press the delete button. The deletion is immediately reflected in the composite model and cannot be undone.

Additional target components can be added by pressing the "Add" button on the panel. This causes a new default target component to be added to the composite model and displayed in the "Single Component Parameters" panel. The user can then modify the added target component.

NOTE: Optical interferometers require fringe tracking on a bright compact component, which effectively becomes the phase center. It is the user's responsibility to construct a composite model that satisfies this requirement. Also, real interferometers have field of view limitations, and the user must be mindful of this when constructing a very extended object or one that contains components placed at large RA and DEC offsets.

Image Upload Panel

The user can bring up the "Upload Image" panel by selecting the "Upload Image" option in the "Mode Selection" panel. The panel allows the user to upload an arbitrary brightness image by selecting a FITS file from the users local disk. The panel displays a "No Image Uploaded" message until the user successfully selects and reads a FITS image form a FITS formatted file.

Pressing the "Upload FITS Image" button brings up a file selection dialog which allows the user to browse for the FITS file to be uploaded. The "No Image Uploaded" message is then replaced by the uploaded brightness image. The user must specify the pixel scale of the image by entering it (in units of milli-arcsec/pixel) in the Pixel Scale input box.

NOTE: the FITS format supports standard, but optional, keywords to specify the image plate scale and orientation on the sky. However the VMT2 makes no assumptions about the presence of these optional keywords. The pixel scale must be entered in the Pixel Scale input box, as described above, and the image orientation is assumed to be: East = Left, North = Up.

NOTE:The image orientation can be flipped to East = Right from the File Pulldown Menu: Settings->Settings and Preferences.

Currently, the VMT2 is limited to uploading FITS images at most 512x512 pixels in size. If an uploaded image does not have a number of pixels that is a power of 2, the VMT2 will zero-pad around the input image to the nearest power of 2.

When the Keck Interferometer is selected, the Image Upload Panel displays a KI Mode Selection Panel in which the user can select either of two modes, the visibility mode ("V2 Mode") or the Keck nuller mode ("Nuller Mode").

In Visibility Mode, the VMT:

     ¥  disables the Null Depth observable option in the Plot Tab.

     ¥  disables the Null Depth Error field in the Instrument Parameter Panel.

     ¥  sets the Null Depth data to "null" in the Simulated Data Tab.

In Keck Nuller Mode, the VMT:

     ¥  disables the Visibility Modulus and Visibility Squared observable options in the Plot Tab.

     ¥  may modify parameters in the Wavelength Parameters Panel valid to KI Nuller Defaults.

     ¥  disables the Visibility Squared Error field in the Instrument Parameter Panel.

     ¥  sets the Visibility Squared data to "null" in the Simulated Data Tab.

Because the Nulling observables for the Keck Interferometer require a time consuming calculation, a suppression option is also provided in this case. When selected, all subsequent nuller calculations are suppressed. When deselected, the nuller calculation is immediately calculated and for each subsequent modification to any control panel input. A progress bar is provided to inform the user of the progress of the nuller calculation. The length of the nuller calculation is dependant upon the number of hour angle observation points specified and number of spectral channels. If these parameters are reduced, the nuller calculation is quicker.

Plot Content Selection Panel

The "Plot Content Selection" panel allows the user to select the content of the displayed observables. This panel is enabled only when the Plot Tab is displayed.

The "Plot Content Selection" panel allows the user to customize the plot content by selecting one of the following observables on either axis:

     Visibility Squared

     Visibility Modulus

     Null Depth (for KI only)

     Baseline Length (in meters)

     Baseline Length (in millions of wavelengths)

     Hour Angle

     U Coordinate (in meters)

     V Coordinate (in meters)

     U Coordinate (in millions of wavelengths)

     V Coordinate (in millions of wavelengths)

     Position Angle (in degrees)

     Zenith Angle (in degrees)

     Wavelength (in microns)

For details on the algorithms employed to calculate these observables, please refer to Appendix B of the VMT User's Guide.

Model Selection

In "Analytical Models" Mode, the "Model" selection pulldown menu in the Plot Content Selection panel, allows the user to select one of three options to view the observables:

* Single Component computes and displays the selected observables for the component currently highlighted in the Target Model Components panel described earlier, using the fractional flux that was entered by the user,

* Single Component f=1.0 same as above but placing all the flux in this component,

* Composite displays the calculated observables for the composite model.

* Image Upload this option is not selectable by the user, but automatically set in upload image mode.

Other Plotting Options

In order to improve the readability of the plots, when the user specifies the spectrometer option (see below), the VMT provides the user an "Include" option to plot the selected observable for all the spectrometer wavelengths or for only the middle wavelength. Likewise, if a plot as a function of wavelength is selected, the user has the option to plot the selected observable for all the hour angle samples, the first hour angle sample, the middle hour angle sample or the last hour angle sample.

Instrument Parameter Panel

The Instrument Parameter panel enables the user to specify the parameters specific to an instrument, i.e. at this time the characteristic errors in V2 or null depth. These errors are applied to all the simulated data, to facilitate comparison of simulated data with changes in the visibility curves as the model parameters change.

Wavelength Parameter Panel

The Wavelength Parameter panel allows the user to select among several spectral options. Because currently we only support grey surface brightness, these options only affect the spatial frequencies (u and v). The options include a monochromatic calculation at the user specified center wavelength (in microns), broadband calculation in a user specified spectral band (defined by the upper and lower limits in microns) and a spectrometer option specifying a number of spectral channels within a band.

For the broad bands, we allow the user to select any lower and upper wavelength, but also provide a list of common astronomical bands. At this time these bands are all assumed to have a top-hat shape.

Observation Parameter Panel

The Observation Parameter panel enables the user to define the observation time span, in terms of start and end Hour Angle, and sampling interval.

Calibrated Data Overlays (OI-FITS)

The VMT provides the user with the capability to overlay calibrated data, in the OI-FITS format (an IAU standard, see http://www.mrao.cam.ac.uk/research/OAS/oi_data/oifits.html). The "Read OI-FITS File" under the File Pulldown Menu will prompt the user to browse for an OI-FITS formatted file and will parse and overlay the data in the vis and vis2 data tables associated with each (details are further described in subsequent sections).

Display Tabs

The VMT has a center display panel that consists of a number of tab options which allow the user to view the predicted simulated observables (both in graphical and textual formats), summary information about the target and instrument being simulated, and to customize the control panels to the user's preference.

Plot Tab

The plot tab allow the user to view the simulated observables in a plot or graphic context. The user controls the content of the plot in the "Plot Content Selection" panel described earlier.

The plot contains many default settings which can be customized by right clicking on the plot. The user can customize properties such as the title's text, font and color, the plot axes text font, color and range settings and the plot lines types and colors.

Chart Properties Option

The Chart Properties panel can be brought with a right mouse click on the chart and selecting "Properties...". This panel contains the tabs "Title", "Plot" and "Other".

The "Title" tab allows the user to modify the properties of the chart's main title such as the name, the font and color of the title.

The "Plot" tab allows the user to modify the properties of the plot. These properties include the same properties of the main chart title (name, font and color) but for each of the domain and range axes labels. The user can select the "Domain Axis" or "Range Axis" tabs to scale the plot and/or customize the tick mark properties for either the domain or range axes respectively. The "Appearance" tab allows the user to modify the appearance of the plot including the thickness of the plot line(s), the plot's background color, and plot orientation (vertical or horizontal).

The "Other" tab allows the user to choose whether or not the fonts of the chart are "anti-aliased", the background color of the chart.

Save and Print Options

The "Save as..." and "Print..." options allow the user to save and print the chart in the downloaded executable version.

Zoom In and Zoom Out Options

The "Zoom In" and "Zoom Out" options allow the user to zoom in or zoom out on the plot for either the range and/or domain axes. The user can also zoom in on the data by left clicking and dragging over a subset of data points to be expanded in a top left to bottom right motion. Dragging the mouse in any of the three alternate ways (top right to bottom left, bottom right to top left or bottom left to top right) causes the data to be re-centered.

Auto Range Option

The "Auto Range" option turns the automatic scaling feature to be turned on. The right-click->"Auto Range" option is simply a short cut for going through the chart "Properties.." option. To reset the scaling, the user must right mouse click and select "Properties->Plot->Range/Domain Axis".

Simulated Data Tab

The "Simulated Data" tab provides an ASCII textual representation of the calculated observables in a tabular format.

The downloadable version of the VMT provides the capability to save this data in a text file (in the Menu Bar select File->Save Prediction Data). The format of the data file allows for the easy importing into other programs for manipulation. In future releases we plan to export data also in the IAU standard for optical interferometry (OI-FITS).

Model Tab

The "Model" tab ("Analytical Models" mode only) provides a list of all the parameters of each individual target component within the target composite model.

Instrument Tab

The "Instrument" tab provides a summary of the selected instrument configuration.

FITS Tab

The "FITS" tab ("Upload Image" mode only) provides an interface to view the contents of the uploaded FITS file which contains the arbitrary brightness image. Both the primary header and image itself can be viewed by selecting the appropriate sub-tab. The Image tab provides a "gamma" slider control which...

OI-FITS Tab

The "OI-FITS" tab (available in either mode but only when OI-FITS data exists) provides an interface to view the contents of a user uploaded OI-FITS file. All file extensions and tables are read in and a corresponding sub-tab is created to allow the user to view any extension of interest.

For a description of the OI-FITS format (an IAU standard) we refer the reader to: http://www.mrao.cam.ac.uk/research/OAS/oi_data/oifits.html

To read in an OI-FITS file, the operator selects "Read OI-FITS File" from the File pulldown menu. The visibility data (from the OI_VIS tables) and the visibility squared data (from the OI_VIS2 tables) are read in from all the tables within the file and associated with their respective target IDs as defined in the OI_TARGET table.

The "OI-FITS Data" sub-panel appears in the control panel allowing the user to select the data associated with one or more individual targets from the file. The targets in the list can be selected contiguously by clicking on the first desired target and while holding down the shift key, selecting the last target or individually by holding down the control key and clicking (which toggles the selection on and off) on the desired target.

The OI-FITS data are displayed in the plot (plot tab), together with the simulated data. Note that some observables listed in the "Plot Content Selection" X and Y Axis options may not exist or be derivable from the contents of the file uploaded (depending on which of the OI-FITS optional tables are present); those quantities will be disabled from the X and Y axis options in the "Plot Content Selection" menu.

In the Image Upload Mode, the u and v values of the data in the OI-FITS file are also overlaid on the visibility modulus image (in the modulus tab), together with the u and v values of the simulated data.

The "Remove Data" button removes the loaded OI-FITS data from the system. To reload the same data or a new OI-FITS data set, the user needs to re-select the "Read OI-FITS File" option from the File pull-down menu.

NOTE: the philosophy adopted by the VMT2 is that when the user has uploaded an OI-FITS file, the contents of all the VIS and VIS2 tables are plotted along with the simulated data. No attempt is made to reconcile the parameters of a simulation with the contents of an OI-FITS file. Also, the VMT2 controls, e.g. wavelength selection or HA coverage, only act on the simulated data, and do not filter the OI-FITS data

Image Tab

The "Image" tab ("Upload Image" mode only) displays the uploaded brightness image. The tab displays "No Image Uploaded" in image upload mode before an image has been uploaded or after an unsuccessful attempt to load an image (e.g. due to an incorrect FITS formatted file).

While over the displayed image, the mouse is tracked and it's xy coordinates and associated brightness value from the uploaded image are displayed at the bottom of the tab.

The "Zoom In" and "Zoom Out" buttons allow the user to zoom in and out respectively. When the limits of the Zoom In and Out features have been reached, the respective button becomes disabled.

The "Gridlines" button shows/hides gridlines overlaid at the labeled axes tick marks.

2D Vis Modulus Tab

The "2D Vis Modulus" tab ("Upload Image" mode only) displays the 2D visbility modulus for the uploaded image, along with the uv values of the simulated data. The tab displays "No Image Uploaded" in image upload mode before an image has been uploaded or after an unsuccessful attempt to load an image (e.g. due to an incorrect FITS formatted file, FFT processing error, etc.).

While over the map, the mouse is tracked and it's uv coordinates and associated visibility modulus value are displayed at the bottom of the tab. When the mouse is clicked within the map image, the crosshairs "snap" to the closest simulated data uv point.

The "Zoom In" and "Zoom Out" buttons allow the user to zoom in and out respectively. When the limits of the Zoom In and Out features have been reached, the respective button becomes disabled.

The "Gridlines" button shows/hides gridlines overlaid at the labeled axes tick marks.

The "Line Profile" button allows the user to specify two points on the modulus map (via mouse clicks) and displays the profile in a two dimensional line plot. The operator can press the "Done" button to return to the previous panel.

Nuller Response Tab

The "Nuller Response Image" tab ("Upload Image" mode and only for the KI) displays the Nuller Beam Pattern; with the same pixel scale as that entered by the user upon uploading their (FITS) brightness image. The tab displays "No Image Uploaded" before an image has been uploaded or after an unsuccessful attempt to load an image (e.g. due to an incorrect FITS formatted file).

The user has the option to select the nuller beam pattern as calculated at the first, middle or last Hour Angle observation points. In spectrometer mode, the user also has the option of choosing the shortest, middle or longest wavelength.

The "Overlay Image" button allows the user to toggle between displaying the nuller response beam pattern only or also super imposing the uploaded brightness.

While over the map, the mouse is tracked and it's xy coordinates and associated Nuller Response value are shown at the bottom of the tab.

The "Zoom In" and "Zoom Out" buttons allow the user to zoom in and out respectively. When the limits of the Zoom In and Out features have been reached, the respective button becomes disabled.

The "Gridlines" button shows/hides gridlines overlaid at the labeled axes tick marks.

Settings Pulldown

The "Preferences and Settings" option provides the capability to set system preferences such as customizing the configuration of the sub control panels in the left and right control panels. The placement of each sub panel can be customized by moving it to the left or right side of the GUI, moving it up or down within either the left or right control panel or hiding it from the GUI altogether.

The initial default configuration can be restored by pressing the "Reset Configuration" button.

Help Pulldown

The "VMT Help" option from the File Puldown Menu, allows the user to select a help subject from a list of topics to be displayed in the tab panel. The spplet version contains a button which allows the .pdf version of the User's Guide to be displayed in a new browser session (ensure your browser has popup blocking disabled).

The "About VMT" option provides information about the VMT and it's environment as well as third party software and licenses that it incorporates.

Getting Help

For additional help please refer to the full VMT User's Guide available online at http:\\nexsciweb.ipac.caltech.edu/vmt. For questions or comments regarding the VMT, please use our helpdesk web form also available at http:\\nexsciweb.ipac.caltech.edu/vmt.