SHIPsData

This wiki area is a dedicated workspace for the NITARP 2013 team SHIPs.

Flexible Image Transport System

A file format used by astronomers to store images, spectra, tables and lots of other things that are data-like in nature (i.e. no one stores a document in FITS format, although this is possible). For images, FITS allows you to keep intact all the value as record by a telescope with each pixel of the image.

References

• What is FITS?
• FITS support office
• List of FITS image viewers and converters?

Primary components of FITS images for our purposes

• We are talking about images here. FITS can also store spectrum, tables, anything else really.
• Header. Contains 'meta' information about the data. At minimum it should simply describe the form factor of the data (2D, 1D, etc.). It has no maximum limits, but practical limits truncate it to what is useful. For our purposes, we need to particular pay attention to a subsection of the header known as the World Coordinate System (WCS, for short, see next item). Header also should tell you when, where the data were taken. What filter was used? And, anything else that the astronomer, observatory thought you ought to know for your science. Look at the NGC 28 image headers to get some idea of what is stored. The FITS header is stored as text strings (You can even read them using typical text readers). The data, however, is stored in binary format and is not pretty to look at. All information in a FITS header text strings is organized in a series of Keyword=Value type of sentences. Further, there is some standardization on what names to you for some specific keywords. For examples, NAXIS=2 tells you that the image has two dimensions. NAXIS has been established as one of those "standard" keywords that one would look for to find how how many dimensions the data has. If this is missing from the header, FITS reader software will fail. NAXIS is an example of mandatory keywords.
  • A gory list of FITS standard keywords. http://heasarc.gsfc.nasa.gov/docs/fcg/standard_dict.html
  • Though, observatories and individuals are fond of defining their own keywords. Then, it becomes their responsibility to explain what they are and how to use them.
• WCS. A subsection of the FITS header. This relates the image coordinates in pixels to a different coordinate system. In Astronomy, the most commonly used coordinate system is the Equatorial one (Right Ascension and Declination). But, any coordinate system (just about) is possible. Another commonly used astronomy system is the Galactic coordinate system.
• Data. This is, of course, what all the FITS hullabaloo was invented for. Data has many meanings here. For our purposes, we mean image data. A typical astronomy image is a two-dimensional array (or table, if you prefer). Each pixel has its own value. The FITS format simply stores each of these values in this data section. A FITS reader will reconstruct the geometry (2-Dimensions in our typical case) by looking at the header first to find this information and then appropriately reading and populating an array (or table) for you.

Tools

ds9

http://hea-www.harvard.edu/RD/ds9/site/Home.html

Luisa's tutorial: http://coolwiki.ipac.caltech.edu/index.php/NITARP_tutorials

ds9 exercises

Load an image.

Change the stretch between log, linear

Change color table

Change scale between displaying all values to zscale.

Change scale between two fixed values.

Zoom/pan to different parts of the image, isolate a single protester

Mark a region, save a region.

Load a region

Display two images side by side

Align the two side-by-side displayed images using their astrometry.

Display two images by blinking between the two.

Use 'fixed cursor' to locate the same star on two side-by-side displayed images.

Find a particular position (ra,dec) on the image.