The Chandra Observation Visualizer

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ObsVis is a tool to aid in observation planning which allows the inspection of sky images with overlaid instrument fields-of-view (FoV). ObsVis interfaces with the SAOimage DS9 image display tool, and facilitates detailed manipulation of Chandra pointing and instrument parameters.

ObsVis is available as part of the CIAO software or as a standalone software package.

If you are interested only in interactive plotting of Chandra's roll, pitch, and visibility for a selected target, use the PRoVis webpage.

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Here we provide a basic example of using ObsVis. For more detailed information, refer to the help file.

Say you want to image M33 with Chandra. It's a good idea to see when it is visible by Chandra before choosing an appropriate roll angle for your visualization of the field of view. Go to the CXC PRoVis webpage. To use the cataloged coordinates, type "M33" (without quotes) in the Target Name box and click the Resolve Name button. After the coordinates appear in the Target Coordinates box, click the Generate Plot button. The resulting plot shows the Chandra roll/pitch/visibility of M33. Since it is best to avoid time-constrained observations, a likely roll angle for M33 (covering a large fraction of the year) is 120 degrees.

Once you have downloaded and installed ObsVis, start it up by typing obsvis. The ObsVis GUI will open, along with SAOImage DS9.

Say your primary interest is to image the M33 nucleus with ACIS-S3, but S2, I2, and I3 will also be turned on for archival use. On the ObsVis GUI, click on ACIS-S under Instrument. In the ACIS Chips instrument detail, uncheck S0, S1, S4, and S5; check I2 and I3. Type "120" in the Roll box and "M33" in the Target Name box. Then click the New FoV button. A new Field of View (FoV) labeled "fov0" (the default) will appear in the table at the bottom of the GUI.

After requesting a new FoV, an SAO-DSS Server box will open with the object coordinates and the DSS image will be retrieved and displayed in DS9. The M33 catalog coordinates are at the aimpoint. The red marker displays the size of the default Chandra dither pattern.

The DS9 display may be adjusted via ObsVis to create a nice proposal image. Open the "Preferences" dialog from the "Edit" menu. To remove the CCD chips labels, for instance, select the "FoV Defaults" tab and uncheck "Display Chips Labels". The DS9 display is updated when "Ok" is clicked.

In the following DS9 display, the chip labels have been turned off. The image zoom is set to "zoom 1/2" and the color is set to "HSV". The DS9 "File → Print" menu can be used to save the image in several file formats. We recommend printing to a Level 1 postscript file for best results with latex and PDF generation.