Worksheet 3 - Reading and browsing data#

Following on from Worksheet 2, you can now read the EIS FITS file from the command line:

IDL> data=obj_new(‘eis_data’,filename)

data is an IDL object. Information is extracted from the object through a large number of methods and some examples are given below.

To determine the coordinates of the center of the raster, do:

IDL> xcen=data->getxcen(/raster)
IDL> ycen=data->getycen(/raster)

To find the exposure time for each exposure of the raster, do:

IDL> exp=data->getexp()

A single data window can be extracted by doing:

IDL> wd=data->getvar(195.12)

where the specified wavelength is used to pick out the data window containing that particular wavelength. The first dimension of WD is always wavelength, the second is always solar-Y, and the third can be either solar-X or time depending if the observation was a raster or a sit-and-stare observation.

A complete list of methods is obtained by doing

IDL> data->display_methods

while more detailed information on some methods is given elsewhere on the EIS wiki.


For these exercises you will need to refer to the EIS object methods page.

  1. Create and plot an IDL map for the Fe XII 195.12 line by taking the moments of the line.
  2. Now use the getvar() method to extract the 195.12 wavelength window. Sum the 3D window over the wavelength direction (use the IDL total() routine), and plot the resulting image. How does it compare to the map image plotted above? See the object methods page for why it is different.
  3. Using the following commands, can you work out the direction that EIS rasters? (east-west, or west-east)
IDL> ti=data->getti_1()
IDL> sec=data->sec_from_obs_start(ti)
IDL> xpos=data->getxpos()