Video Demos and Tutorials
It can be difficult to write documentation for graphical programs. There are many subtle details that can get lost or overlooked. The CXC has therefore started to prepare a series of video screencasts providing demos and tutorials of various components of CIAO.
The following videos are linked from here.
- How to load images and event files into ds9
- Customizing the ds9 user interface
- Using multiple frames with ds9
- Setting region properties in ds9
- Tri color images in ds9
- 3D binning of event files
- Using masks with ds9
- An introduction to the ds9 catalog tool
- Basic statistics
- Getting Chandra coordinates within ds9
- Extracting Spectra, Light Curves, and Radial Profiles
- CIAO source detect tools
- Image Processing
- First Light Animation
How to load images and event files into ds9
CIAO provides the ds9 as the primary interactive imaging tool. Chandra's primary science data product is the event file, which may be unfamiliar to users coming to X-ray astronomy from most other wavelengths where images are used.
This demos shows how to load a Chandra event file (or other high energy mission) into ds9, and how to select different filters and coordinate systems.
Customizing the ds9 user interface
The ds9 user interface can be reconfigured to optimize the user's work-flow; suppressing or exposing key information to the accelerate the user's analysis. It is also designed to make repetitive tasks easier by allowing one to tear off menus so that common tasks are only one click away.
This tutorial describes the terminology and demos how to reconfigure the GUI to suite the users preference.
Using multiple frames with ds9
ds9 allows multiple frames to be loaded. These may represent the same area of the sky in multiple wavebands, a collection of similar objects (eg SNRs), a comparison of simulated versus observed data, etc.
This demo shows to create and manage multiple frames using Chandra data of the Rho Oph fields: obsids 635 and 637.
Setting region properties in ds9
Users can create regions in ds9 that can be used to designate sources or background. Within ds9 itself these are largely just annotations, however, if a users supplies a bit of extra information, highly complex regions can be constructed in a way that CIAO tasks such as dmextract can be used.
This demo shows to create source and background regions, associate them with each other, and how to prepare that information for CIAO.
Tri color images in ds9
Three color images are popular way to encode, in a scientifically meaningful way, multiple representations of the same region of the sky. Typically this is done with each of the primary red, green, and blue colors mapping to certain energies -- be they X-ray energies or even wide band X-ray, radio, optical composites.
This demo shows to make such images with CIAO and ds9. It also shows an example where the 3 colors represent time instead of energy.
3D binning of event files
A Chandra event file is in some sense a four dimensional data cube: RA, Dec, Time, and Energy -- but very sparsely populated. By displaying an image we lose information about the other two axes. We can bin the data into 3D (or even 4D) cube and use ds9 to display the 3D cube as a series of slices through the data, one 2D image at a time.
This demo shows to use ds9 to make 3D data-cubes in energy and time, essentially making a per-pixel spectrum and per-pixel light curve. ds9 also has special 3D shapes that allow one to perform some rudimentary analysis on these datasets.
Using masks with ds9
Masks are binary images that represent some area of interest; some examples of where are showing edges of detectors, outlines of sources, or interesting contour levels. ds9 allows such masks to be overlaid onto images with adjustable transparency.
An introduction to the ds9 catalog tool
The ds9 catalog tool allows users to annotate their images with markers for sources from many different catalogs (including the Chandra Source Catalog and users own source list, eg output from CIAO's wavdetect, celldetect, and vtpdetect). More than that, the user can interact with the sources and the source lists. Advanced user can even connect to the catalog tool to other applications, eg topcat and cscview , where advanced analysis can be performed.
This introductory tutorial shows how to load a catalog, basic interactions, and how to generate complex annotation schemes. Look for future demos showing some of the advanced features mentioned above.
The version of ds9 packaged with CIAO has been configured to automatically load a suite of analysis tasks which is given the code name "dax", ds9 analysis extensions. This includes things like getting number of counts in a region (ie aperture photometry), extracting spectra and light-curves, converting between Chandra specific coordinates, and general image processing techniques. Many of the dax tasks are not specific to Chandra and nor specific to X-ray analysis.
This first demo introduces dax and shows how to get some simple statistics about the pixels in a selected region. Under the hood, this runs the CIAO tool dmstat to get things like total counts and centroids.
Getting Chandra coordinates within ds9
Chandra has many spatial coordinates from chip to detector to sky. Not all are represented by the world coordinate systems (WCS) and the CIAO tool dmcoords is needed to do the conversions.
This demo shows how to get into the cross-hair mode and use the dax Coordinate tasks to do various conversions.
Extracting Spectra, Light Curves, and Radial Profiles
One of the most powerful dax tasks is the ability to create spectra and light curves very simply from the ds9 GUI without having know all the behind the scenes CIAO syntax used by dmextract.
The video was created with an "old" version of CIAO (i.e. earlier than CIAO 4.12), and so shows plots created using the ChIPS plotting package. As of CIAO 4.12 the CXC no longer provides ChIPS and plots are created either using DS9 directly (plotting support has been enhanced significantly in DS9 version 8.1 released with CIAO 4.12) or with Matplotlib.
CIAO source detect tools
There are many different image processing tasks available in CIAO -- and strung together they can be powerful tools for any astronomer.
First Light Animation
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