Example CASPER Session

This is an introductory tutorial for first-time users of CASPER. It walks you through some of the more common steps encountered in running CASPER, introduces the most useful functions, and should give you a feel for the program. It is assumed that you have already setup CASPER for your system and are familiar with using your particular windows environment. If you have not yet installed CASPER, you should look at the Installing CASPER Guide. At your shell prompt, enter the command 
csh> CASPER
This will initiate an IDL session and run the pre-compiled CASPER IDL code (you must have run the command CASPER_COMPILE at least once before for this to work). Once initiated, CASPER will put up a title window and run through its initialization procedure. It will then create the top level CASPER window, followed by a file selection widget that will ask you to select the tour file to be used for this session. You can select one of the names with the left mouse button and the name is copied into the text widget at the bottom of the screen. For this session, select a tour file that is valid for the Saturn orbital tour (e.g. T18-5), not the cruise phase. Click on the OK button and this tour file is loaded. You are now ready to start using CASPER.

Note:  You can make CASPER load a tour file automatically by choosing Save Defaults under the Utilities menu of the main CASPER widget.  The next time you start CASPER, the "Select a Tour File" widget will not appear.  You can then change the kernel by selecting SP Kernel Tools and Change Tour Kernel.

CASPER has a Help function that displays help on various widgets as the mouse pointer moves over them. This function can be turned on and off by selecting Context Sensitive Help under the Help menu on the top level window. Do this now. A window appears in the top right hand corner, and as you move the pointer over the CASPER window, it updates the help text in the help window. Select Context Sensitive Help again to switch this function off.  Most widgets in CASPER also have a Help button, usually at the bottom of the widget.  Clicking on the Help button creates a window with text describing the purpose and functioning of the widget. It is a good idea to close CASPER windows, such as help windows, when you are finished with them. The buttons on the CASPER widget allow you to start any one of six tools. For this session we are going to use the Target tool. Click on the Target button and the Target tool window will come up. To create a plot, Target needs three pieces of information - a target body, an observer (or spacecraft), and a plot time. These are entered via the Session Data Entry window, which you can bring up by either selecting New Plot... under the File menu, or by clicking the icon with the picture of a clock.

There are a lot of functions on this window, but for now we'll just enter a time, target, and observer. These are all at the top of the window. Click in the text entry widget where it says Plot Time (UTC) and enter the following text: 

        2005 6 7
and then press the RETURN key. NOTE: when using text entry widgets it is important that you ALWAYS press RETURN to enter your text into the CASPER tools. On pressing RETURN, you will see that the numbers you entered are interpreted to produce the UTC string: 
        2005 JUN 07 00:00:00.000
Various other styles of time entry can be interpreted by CASPER. These are explained in the help file for the Session Data Entry Widget.

Next, select a target body using the droplist widget. Click on the widget, and a list of targets will appear. Move the mouse to highlight the target you wish and release. The droplist button should now display the name of your target. For this example you should select SATURN. For the Saturn tour, the observer you select should be CASSINI SIM.

All the user-entered data that is required to make a plot is now in the widget buffer.

To draw the plot, click on PLOT in the upper right hand corner. The widget will iconize and the cursor will change to an "Hourglass" as internal calculations are carried out. The plot of Saturn will appear in the main drawing widget after a few seconds.

Use the horizontal slider to move the plot left and right. After each manipulation, the plot is recalculated (you are not sliding a plot larger than the display area). Similarly the left vertical slider will manipulate the plot up and down. The Arrow buttons may be clicked on to give small increments in position. The right vertical slider controls the Zoom of the plot. The Reset button at the junction of the position sliders will center the plot again and reset the zoom to the starting value.  You can also add many graphics to the plot such as stars, orbits, exobase, among others.  Just click on the graphics menu and then click on the graphic you wish to be displayed.  Each graphic has an on/off function (see Turning ON/OFF Graphic Features);  if the graphic you desire is set at ON already, then don't click on it (clicking on it will turn it off).  However, if it is set at OFF, then click on it to turn it on. Before you create an observation, or "Module," with CASPER, "turn on" one or more instrument Fields of View (FOV).  This will instruct CASPER to display the footprints of each instrument FOV you select when you create an observation.  Select which FOV footprints will be drawn either by clicking on the short-cut button with a cartoon of different FOV shapes (6th from the left), or by

selecting FOV Select from the FOV Tools sub-menu in the Sequence Design menu.

This creates the FOV Selection widget.  Instruments are divided into groups controlled by a droplist widget at the top of the FOV Selection widget.  For this example,

choose the ISS group and then the ISS Wide Angle Camera.

You may turn on as many FOVs as you like, but the CASPER plot may become cluttered if many FOVs are turned on.  When you are finished,

click on the Done button

to close the widget.  It is a good idea to get in the habit of closing widgets that you are finished with to avoid exhausting your computer's memory.

You are now ready to create an observation with CASPER.  To create a module on the plot, either

select the Modules... menu item

which you will find under the Mosaic Tools sub-menu in the Sequence Design menu, or simply click on the button with the picture of six overlapping squares. This creates the Module Selection Widget.

The Module Group droplist allows you to select different module groups. Modules will be added to CASPER for future releases.  For this example,

select GENMOSAB_IVP under the Mosaics and Scans droplist

(this should be highlighted by default). Then

click on the Generic button

to create the GENMOSAB_IVP widget.

The GENMOSAB_IVP module is defined for Optical Remote Sensing (ORS) instruments which are boresighted along the Cassini -Y axis.  It is a box mosaic.  CASPER offers you several different methods of specifying the parameters for your GENMOSAB_IVP mosaic.  You may specify the number of Scans and Footprints, such as a (3 by 4) mosaic, or you may specify the amount of overlap between fields of view.  For the latter, you must select an instrument FOV to be used for the overlap calculation.  This is not the same as the FOVs which are selected to be drawn by the FOV Selection widget.

Under the User Specifies droplist, select % Overlap.

Click on Make It So.

CASPER should beep and display an error message in the bottom of the widget.  You have requested overlap, but you have not specified an instrument FOV for the overlap calculation.  Near the top of the widget,

Click on Select Instrument

for a Field of View.  This creates the Instrument Selection widget.  It is not the same as the Field of View Selection widget. Again, this has nothing to do with what is displayed, just with what is calculated for FOV overlap.  To illustrate this point,

select ISS Narrow Angle Camera from the ISS group.

This closes this widget and copies the selected instrument to the GENMOSAB_IVP window.  The Coverage Selection droplist should be showing Corner Ra/Dec Box which means you will specify the coverage area by drawing a box on the Target plot.

Leave the other parameters at their default settings.

Click on Make It So.

Bring the Target window forward if it is obscured, but be careful NOT to click in the plot area just yet as this starts the box drawing process. At this point you may resize and adjust the Target plot.

Draw a small box on Saturn (about 1 degree by 1 degree, using the RA/Dec grid as a guide) with the left mouse button.

CASPER will compute a GENMOSAB_IVP observation to fill that box.  The spacing of the pointings (indicated by numbers) is determined by the 0% overlap of the ISS Narrow Angle Camera.  You will notice, however, that the FOVs drawn overlap by a considerable amount.  That is because you are drawing the ISS Wide Angle Camera, but you computed overlap for the Narrow Angle Camera.  To see that there is indeed a 0% overlap of the ISS Narrow Angle Camera,

Select FOV Select from the FOV Tools sub-menu of the Sequence Design menu

Select ISS Narrow Angle Camera from the ISS group in the FOV Selection widget

Click on Update in the FOV selection widget.

The Target plot should now display both ISS WAC and ISS NAC FOVs for the mosaic, and the ISS NAC FOVs should be aligned with 0% overlap between them in both directions.

You can add further mosaics if you wish.

CASPER has its own internal file format for saving and loading mosaics at present.

To save your current mosaic, click on the button with the template picture above an arrow pointing at a floppy disk. You will be prompted for a file name. If you do not supply a .mos extension, CASPER will automatically append one.

The picture with the arrow pointing away from the floppy disk will load a previously saved mosaic file. You may also write an ASCII output file for use with other programs that contains all information on your CASPER session by selecting save CASPER output ... from the Target File  menu. CASPER cannot reload from a CASPER output file, however.

There are two ways to create a plot in skymap:  1) from Target, or 2) from scratch.
1)  Once a plot is created in target, that information is saved in skymap also.  You can simply start the skymap tool (by clicking on SKYMAP in the main CASPER widget) and a plot will appear in skymap with the same specifications as that in target.  Note, however, that Target must still be open with the desired plot displayed;  once you erase the plot in target, it will not appear in skymap.
2)  The procedure is identical to that of creating a plot in target, except that the skymap tool is opened originally instead of the target tool. There are two ways to create a plot in 3D-view:  1) from Target or Skymap, or 2) from scratch.
1)  Once a plot is created in target or skymap, that information is saved in 3d-view also.  You can simply start the 3d-view tool (by clicking on 3DVIEW in the main CASPER widget) and a plot will appear in 3d-view with the same specifications as that in target or skymap.  Note, however, that Target or skymap must still be open with the desired plot displayed;  once you erase the plot in target, it will not appear in 3d-view.
2)  The procedure is identical to that of creating a plot in target, except that the 3d-view tool is opened originally instead of the target tool, and the session data entry widget is accessed by clicking on the Main menu and then selecting New Plot. To make a new plot, select New Plot... from the File menu or click on the clock icon. You will be prompted to save the mosaic data if you wish. Then the current plot will be cleared and the Session Data Entry window will be uniconized. This time we will plot a flyby of Titan. For this we need to use the CASPER link to the Events program. Click the EVENTS button on the Session Data Entry window (or alternatively you can run Events using the Events button on the main CASPER window). This creates the Events window, which has options to load and process Events output, to save and load CASPER processed Events output (which is quicker to load), or to run events interactively. This is what we shall do, so click the Run Events button to run an events session.

This creates the Run Events window. As Titan Flyby's are relatively quick to calculate, we will run Events over the entire tour, so make sure the Ephemeris Start and Ephemeris End buttons are selected (pushed in).

The CPU time to be used by Events can be left at 3000 seconds and CASPER uses a UTC time format. As we are not saving the Events output, you do not need to change the default output file setting.

From the Event Type droplist, select Flyby. This will cause the Targets list to update and display all possible flyby targets. Find and select Titan. There is no subtype for a Flyby Event.

At this point there are two ways to proceed. You can either use the Add button to add the Event to the Event buffer and then proceed to set up new events to calculate. If you do this, clicking the Run button will run Events on all the listed events in the buffer.

However, if you just wish to run on the one event type, it is quicker to just click Run. CASPER will see that the Events buffer is empty and instead use the event information displayed on the droplist widgets to send to Events. The cursor will turn into a wait state hour glass while Events runs.

When it is finished, the Events window will become active again and contain the results of the Events run. Select one of the Titan flyby times and the data and target will be copied into the Session Data Entry window. Click Plot in this window and CASPER will create a plot of the Titan flyby in the Main Window.

Under the File menu, select Title Plot.... This creates a widget in which you may enter a text string. Pressing RETURN kills the widget and the text will appear in the upper left corner of the plot. Under the Graphic menu, there are features that can be turned on and off in the plot. Select the Background Grid: ON item. This toggles the Background Grid off and if you look in the Graphic menu again, you will see this item has changed to Background Grid: OFF to reflect this. Once you are happy with the plot, you may either save it as a PostScript file using the File menu Save Plot As... item, or print it directly to a PostScript printer using the File menu Print Plot item or clicking the button with the picture of a printer. Once you have completed your work with CASPER, select Quit from the File menu on the main CASPER window. You will be asked if you are sure you want to Quit and if you answer YES, you will end up back at the shell prompt. (You will also be prompted to save any pointing data that may exist).