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#### 8.3.38 `skygrid`

Plots an additional axis grid on the celestial sphere. This can be overlaid on the default sky axis grid so that axes for multiple sky coordinate systems are simultaneously visible. The plots are done relative to the View sky system (`viewsys` parameter) defined for the plot as a whole.

Note that some of the configuration items for this plotter, such as grid line antialiasing and the decimal/sexagesimal flag, are inherited from the values set for the main sky plot grid.

Usage Overview:

       layerN=skygrid gridsysN=equatorial|galactic|supergalactic|ecliptic
                      gridcolorN=<rrggbb>|red|blue|... transparencyN=0..1
                      labelposN=Internal|None loncrowdN=<number> latcrowdN=<number>

All the parameters listed here affect only the relevant layer, identified by the suffix `N`.

Example:

       stilts plot2sky xpix=500 ypix=250 projection=aitoff
                       viewsys=ecliptic
                       layer1=skygrid gridsys1=galactic gridcolor1=HotPink labelpos1=none

`gridcolorN = <rrggbb>|red|blue|...` (Color)
  The color of the plot grid, given by name or as a hexadecimal RGB value.

  The standard plotting colour names are `red`, `blue`, `green`, `grey`, `magenta`, `cyan`, `orange`, `pink`, `yellow`, `black`, `light_grey`, `white`. However, many other common colour names (too many to list here) are also understood. The list currently contains those colour names understood by most web browsers, from `AliceBlue` to `YellowGreen`, listed e.g. in the Extended color keywords section of the CSS3 standard.

  Alternatively, a six-digit hexadecimal number RRGGBB may be supplied, optionally prefixed by "`#`" or "`0x`", giving red, green and blue intensities, e.g. "`ff00ff`", "`#ff00ff`" or "`0xff00ff`" for magenta.

  [Default: `light_grey`]

`gridsysN = equatorial|galactic|supergalactic|ecliptic` (SkySys)
  The sky coordinate system used for the additional grid axes. This is used in conunction with the `viewsys` parameter defined for the plot as a whole to determin what grid lines to plot.

  The available options are:

  - `equatorial`: J2000 equatorial system
  - `galactic`: IAU 1958 galactic system
  - `supergalactic`: De Vaucouleurs supergalactic system
  - `ecliptic`: ecliptic system based on conversion at 2000.0

  [Default: `equatorial`]

`labelposN = Internal|None` (SkyAxisLabeller)
  Controls how and whether the numeric annotations of the lon/lat axes are displayed.

  The available options are:

  - `Internal`: Labels are drawn inside the plot bounds
  - `None`: Axes are not labelled

  [Default: `Internal`]

`latcrowdN = <number>` (Double)
  Determines how closely sky latitude grid lines (parallels) are spaced. The default value is 1, meaning normal crowding. Larger values result in more grid lines, and smaller values in fewer grid lines.

  [Default: `1`]

`loncrowdN = <number>` (Double)
  Determines how closely sky longitude grid lines (meridians) are spaced. The default value is 1, meaning normal crowding. Larger values result in more grid lines, and smaller values in fewer grid lines.

  [Default: `1`]

`transparencyN = 0..1` (Double)
  Transparency with which components are plotted, in the range 0 (opaque) to 1 (invisible). The value is 1-alpha.

  [Default: `0`]

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk