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### 8.1 Plot Parameters

The plotting commands offer a great deal of control over what is plotted and how it is represented, and thus unavoidably have lots of parameters. When looking at the command documentation in Appendix B the Usage sections may look rather daunting. However, the discussion below and the Examples sections should help. Generating a simple plot is straightforward and can be done with only four or five parameters; if you want to represent more complicated data or have specific preferences for appearance then you can consult the documentation for the additional options.

As a simple example, if a file "cat.fits" contains the columns RMAG and BMAG for red and blue magnitudes, you can draw a two-dimensional colour-magnitude scatter plot with the command:

```   stilts plot2plane layer_1=mark in_1=cat.fits x_1=BMAG-RMAG y_1=BMAG
```
Since an output file is not specified, the plot is shown in a window on the screen. This plot window is "live" - you can resize the window, or pan and zoom around it using the same mouse controls as in TOPCAT. To send the output to a PNG file, do instead:
```   stilts plot2plane layer_1=mark in_1=cat.fits x_1=BMAG-RMAG y_1=BMAG out=fig.png
```

We can adjust the plot by inverting the Y axis so it increases downwards instead of upwards:

```   stilts plot2plane
yflip=true
layer_1=mark in_1=cat.fits x_1=BMAG-RMAG y_1=BMAG
```
The parameters of the plot now fall into two groups. Global parameters, without suffixes, make global adjustments to the plot. In this example `yflip=true` inverts the Y axis. Layer parameters, with suffixes, are introduced by a `layer` parameter and grouped together by a given suffix. Each layer group defines a plot layer with content to be drawn on the plot surface. In this case the layer is of type `mark` (draw markers) and the suffix is "`_1`". Global and Layer parameters are described separately in the following subsections.

Next Previous Up Contents
Next: Global Parameters
Up: Plotting
Previous: Plotting

STILTS - Starlink Tables Infrastructure Library Tool Set