A Quick Reference Guide to creating ESO Finding Charts with SkyCat

Perhaps the simplest means to generate ESO finding charts is to rely on the p2fc facility within the p2 (Paranal) and p2ls (La Silla) tools.  In addition, a command line interface to p2fc is available, via the p2api, allowing control over many of the characterisitics of the FC generation.  For more information on p2fc we refer the reader to the p2fc Finding Charts web page.

Another possibility approach is to use the SkyCat plugin, which is described in the following.  It has been developed to make finding charts in an easy and quick way for any instrument. It is a plugin to the Skycat software.


This document summarizes a series of basic steps needed to produce finding charts according to the ESO requirements for Service Mode observations using the basic SkyCat functionalities and a special tool which runs as a plugin to SkyCat itself.

The general guidelines for finding chart preparation can be found on the requirements page for finding charts. This page also contains instrument-specific information (use the menu in the right-hand column to select the relevant instrument).

DISCLAIMER: This document is not intended to be an exhaustive guide to fully exploit the SkyCat tool.


Installation and Startup

The finding chart tool is now distributed as a part of the SkyCat software itself. (It also comes with the FIMS and KARMA packages. Users of FORS or KMOS should use the relevant tool to create their charts).

Loading an Image

Let us start by loading the image of your field in the main Skycat window. There are two ways to do this:

  • select File>Open and specify the FITS file of the image of your target (e.g. in case you have already acquired a pre-imaging frame). Please notice that SkyCat can only handle images in FITS format.
  • select an on-line catalog from the Data-Servers>Image Servers menu. A new window will pop-up, where you can specify the Object Name, its Coordinates, the Equinox, and the Width and Height of the field of view you wish to retrieve (the dimensions of the charts depend on the instrument they are needed for, so please be sure to check the instrument specific requirements). Clicking on the Get Image button starts the query.

REMINDER: whenever possible, finding charts should have similar central wavelength to observations (e.g. DSS images are often inappropriate for near-IR observations).

The image of your object should now be in the main SkyCat window. If you have downloaded it from an on-line server, it is now advisable to save it (File>Save as...) in case, later on, you would like to load it again together with all the graphics (labels, marks, slit positions, etc.).

At this point, everyone is encouraged to experiment with the different options offered in the menu bar, in order to become more familiar with this powerful tool. The View menu contains a wealth of information. If, for instance, the image just displayed looks too small in the main SkyCat window, you can zoom in and enlarge it, by selecting Magnification. As an alternative, you can also change the magnification factor in Scale, or simply by clicking on the capital Z button (or small z button to zoom out) the number of times you deem appropriate. Selecting WCS Info... gives a summary of the World Coordinate System information. By selecting Cut Levels, a new window pops up showing the flux distribution of the selected object and allowing you to optimize the contrast of your image by adjusting the cut levels. The option Pick Object allows you to retrieve information on the coordinates and FWHM of objects present in your field of view, while Image Statistics information can be obtained by selecting Pixel Table....

Once you are satisfied with the appearance of the image displayed and you have checked all the information you may need (e.g. distances between objects in the field by keeping pressed the right button of the mouse), you are just a few steps away from making this chart ESO compliant.

Basic Finding Chart Markup

Let us now add the basic information to the finding chart by selecting File>Make finding charts.... A window will pop up prompting you to enter your Run ID, the PI Name, the List of OBs linked to the finding chart (or any other helpful information in making the association between the chart and the corresponding OBs) and the Band/Wavelength of this chart. Clicking on Draw will add these entries to the finding chart together with a bar indicating the scale of the image and a compass pointing North and East (these will only be displayed if the image has proper WCS information). Also, it will select the correct color table, i.e. black objects on a white background, though you may still have to select the appropriate cuts by hand.

The Location of info pull-down menu allows you to choose where to place these pieces of information on the image. The four pre-defined placements will put the details of the run in the specified corner and the compass and scale in two of the three other corners. As an alternative, you can select the Location of info>user chosen option and you will be asked to click on the image where you want the information to be placed. In either case, all the items can be dragged around by left-clicking on them. Finally, the color of the text, either black, white, blue or red, can be selected with the last pull-down menu named Text color.

All the entries in the Finding chart information window are stored in memory and it is enough to click on the Draw button to display them again. This makes it very easy to produce several finding charts for the same field without having to re-enter everything for each of them. The Reset coords button is used to reset the location of the items when using the Location of the info>user chosen option. If you click on it and then on Draw you are prompted again to click on the canvas to select the new locations. The Clear button deletes all the overlays created by this tool, but not those drawn by other tools such as, for example, FIMS, VMMPS or the standard SkyCat graphical capabilities.

Adding Additional Information

The File>Make finding charts... tool provides a quick and easy way to add all of the mandatory information that has to be on every ESO finding chart: the basic details of the run, a compass pointing North and East, and a scale to indicate the size of the image. In addition to this though, depending on the instrument used and on the type of chart (imaging, spectroscopy, etc) one may be required to add more items to it. Once again, please read carefully the instrument-specific requirements.

Since period 82 the Finding Chart plug-in delivered with the FIMS and VMMPS tools now allows one to draw boxes of arbitrary on-sky size and position angle. This makes it easier to add features on the finding chart such as instrument field of view or slits for spectroscopic observations. In order to draw a box, specify its height and width in arcseconds in the dedicated fields of the plug-in, and hit the button Draw Box. Optionally, you may also specify a position angle, and the coordinates of the center of the box. Once a box is drawn on the image, you may move it around by selecting it and dragging it with the mouse. The coordinates of the center of the box will be updated in the plug-in dialog as you move it along. Similarly, a selected box may be rotated by holding the Ctrl key and the right mouse button at the same time, while dragging one of the selection handles of the box. The position angle displayed in the dialog will be updated once you are finished rotating the box. You may draw as many boxes as you need with this new facility.

More labels and drawings can be conveniently added to the chart by selecting Graphics>Toolbox in the main SkyCat window (this function is disabled in the GUIDECAM package). Doing so will open a window which collects all the graphic tools you need for this purpose.

  • For text labels: first select the Font you wish to use (make some tests and see which font is easier to read once the finding chart is printed), make sure to choose a dark ink for the labels since the image background is light (e.g. by selecting black from Outline), click on the capital A, go back to the main SkyCat window and place the cursor where you want to place your label. Clicking on the spot makes the writing option active.
  • For drawings: depending on which type of drawing you are interested in, you can select one of the remaining drawing buttons at the top of the Line Graphics window. Although they should be self-explanatory, let us make some specific examples. In order to draw a line or a bar, first select the button identified by a line (similar to a backslash), then move to the main SkyCat window, 7and click the left button of the mouse on the starting point, drag it until the ending point, and release it. If, instead, an arrow is needed, you must select one of the options from the Arrow and Arrow Shape menus before selecting the backslash-like button and start drawing. Similarly, you can choose different thicknesses of the line to be drawn by selecting one of the options offered in the menu Width.

Saving Your Finding Chart

Once you are satisfied with the results, the finding chart needs to be saved, to be eventually attached to the OBs and submitted to ESO. The finding charts need to be attached in jpeg format directly to the OBs with the p2 tool. In order to save the chart in jpeg format click on Save to jpeg... in the File>Make finding charts... window to choose the destination directory and write the file on disk (the local directory is the default).

Before submitting the finding chart, print it at your home institution in order to check for its readability and cleanliness. Please note that some popular tools to view jpeg files, most notably xv, do not display the files at full resolution, and the chart may appear of low quality. When attached to OBs with p2, however, the full resolution of the finding charts is preserved.

Additionally, the Print... button can be used to print the chart on a Postscript printer, or save it as a Postscript file. However, let us stress again that only finding charts in Jpeg format can be submitted to ESO!

In addition to saving the finding chart as a jpeg file as described above, you may also want to save the graphics themselves so that you will be able to edit them at a later time. This can be done either as an extension attached to the FITS image (Graphics>Save Graphics with image) or as a stand-alone ASCII file (Graphics>Save Graphics...).

Detailed instructions on how to attach finding charts to an OB for submission can be found on the dedicated p2 tutorial page.

Instrument selector