This is a quick tutorial to help new users get familiar with the GPI pipeline. More detailed documentation of the tools shown here can be found on subsequent pages.
As an introduction to reducing data with the GPI Pipeline, a simple set of data is available on the Canadian Astronomy Data Center (CADC). If it is the first time you visit CADC, you will need to register. Once it is done, go into the gpi directory and download the GettingStarted_tutorial_dataset folder. This contains a small set of data to give an overview of the different types of image and how to process them. All the files are raw data coming from the detector and we will reduce them one at a time.
It is assumed you have successfully launched the pipeline following the previous sections.(If not, see the GPI Data Pipeline Installation & Configuration manual.) Therefore, you should have the two IDL sessions opened with the GPI launcher GUI and the GPI DRP status console below. See Starting the GPI Data Pipeline and Starting the GPI Data Pipeline. The GPI pipeline console should indicate something like:
| Now polling for DRF files in /Users/yourusername/somedirectory/GPI/queue/
The Launcher is a little menu window that acts as the starting point for launching other tools. In this getting started tutorial, we will only use GPItv and the Recipe Editor tools.
Before reducing any files, the best is probably to take a look at the raw data we have using GPItv. Click on the GPItv button on the GPI launcher to open it (See GPItv Viewer User’s Guide for more details):
- Then File->Browse Files...,
- In the new window push the button Change... and select a folder in the GettingStarted_tutorial_dataset.
- The .fits files list should appear.
- As you select one file or another, the GPItv window should refresh and plot the new image.
- Use the GPItv menu File->View FITS headers... to get detailed information for each image.
- Click on the image to center the view on a pixel. Adapt the zoom with the buttons.
|||The reason for these odd exposure times is that GPI IFS exposures are quantized in units of the readout time for the detector, 1.455s. These darks thus represent 3 readout times and 40 readout times, respectively. Because of this quantization, in practice one typically just rounds the durations, so these would be e.g. “4.5” and “58” s exposures - there’s no need to carry around all the significant figures.|
Let’s first give the general method to reduce any file. This will then be applied in the next sections for different particular cases. Only the selected items in the different option lists will change.
Press the Recipe Editor button in the GPI Launcher window and the window below will open.
The principle of the pipeline is based on recipes to reduce files. A recipe includes a list of input files (the ingredients) and a list of primitives to be applied on those files (the actions). Each primitive is an elementary algorithm to be applied on files listed in the recipe. The action can be anything, for instance subtract dark frame or build data cube. There are two kinds of primitives: ones that should be applied on each file and ones that are applied on all files together. For instance, Subtract Dark acts on one file at a time, while Combine 2D images will merge all the files from the list resulting in a single output file. The special primitive Accumulate Images divides the two categories of primitives. All the primitives before are applied to each file, then Accumulate Images gathers up the results, and any primitives after are applied to the entire set.
The numbers of each of the following steps match with the screenshot above.
In the following, these steps will be repeated several times with specific indications.
For every reduction, a gpitv window will open with the result of the reduction and the file will be saved in the reduction folder defined when installing the pipeline. If you don’t want to plot or to save the results, you can change the parameters Save and gpitv of the primitives. To change parameters, select the primitive in the upper right table. Then, its parameters will appear in the bottom right table. Select the value of the parameter and type what ever is asked. Finally, press enter to validate the input.
The dark calibration files for a given integration time can be combined using these amendments to the Recipe Editor usage steps above:
The selected primitives are then:
The GPI DRP Status Console will display a progress bar and log messages while reducing the files.
When reducing calibration files the result is automatically saved in the Calibrations folder. The path to this folder was defined when installing the pipeline and should normally be in the reduced folder (See Configuring the Pipeline $GPI_REDUCED_DATA/calibrations).
The pipeline will look for calibration files automatically by reading the text file GPI_Calibs_DB.txt in the calibration folder (see The Calibration Database). There is a button at the bottom of the GPI DRP Status Console called Rescan Calib. DB to create or refresh this text file.
As for the darks, the wavelength solution calibration files can be created using the Recipe Editor reduction steps with the following additions:
The sample files provided contain neither a Thermal/Sky background calibration file, nor bad-pixel maps so you will get warnings but it should work anyway. How to create such files is described later in this documentation <processing_step_by_step>
A sample of the 2D image with the computed calibration is given below. The green lines are the locations of the individual lenslet spectra. The coordinates of the lenslets are stored in a .fits file cube in the calibrations folder. Use GPItv to take a look to the result.
Here again the method is the same.
All the calibration files are automatically found and the result is a final data cube. The result should be plotted in GPItv at the end of the reduction. Feel free to look at the different wavelengths by changing the selected slice.
Enjoy the first of many data cubes!