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#### 8.3.3 `sizexy`

Plots a shaped marker with variable horizontal and vertical extents at each position. The X and Y dimensions are determined by two additional input data values.

The actual size of the markers depends on the setting of the `autoscale` parameter. If autoscaling is off, the basic dimensions of each marker are given by the input data values in units of pixels. If autoscaling is on, the data values are gathered for all the currently visible points, and scaling factors are applied so that the largest ones will be a sensible size (a few tens of pixels). This autoscaling happens independently for the X and Y directions. The basic sizes can be further adjusted with the `scale` factor.

Currently data values of zero always correspond to marker dimension of zero, negative data values are not represented, and the mapping is linear. An absolute maximum of 100 pixels is also imposed on marker sizes. Other options may be introduced in future.

Note: for marker sizes that correspond to data values in data coordinates, you may find Error plotting more appropriate.

Usage Overview:

       layerN=sizexy shapeN=open_rectangle|open_triangle|... thickN=<int-value>
                     scaleN=<factor> autoscaleN=true|false
                     shadingN=auto|flat|translucent|transparent|density|aux|weighted <shade-paramsN>
                     <pos-coord-paramsN> xsizeN=<num-expr> ysizeN=<num-expr>
                     inN=<table> ifmtN=<in-format> istreamN=true|false icmdN=<cmds>

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

Positional Coordinate Parameters:
  The positional coordinates `<pos-coord-paramsN>` give a position for each row of the input table. Their form depends on the plot geometry, i.e. which plotting command is used. For a plane plot (`plot2plane`) the parameters would be `xN` and `yN`. The coordinate parameter values are in all cases strings interpreted as numeric expressions based on column names. These can be column names, fixed values or algebraic expressions as described in Section 10.

Example:

       stilts plot2plane layer1=sizexy in1=dr5qso.fits shape1=filled_rectangle
                         x1=psfmag_u-psfmag_g y1=psfmag_r-psfmag_z xsize1=exp(psfmag_g) ysize1=exp(psfmag_r)
                         xmin=-3 xmax=1 ymin=1 ymax=3.2

`autoscaleN = true|false` (Boolean)
  Determines whether the basic size of variable sized markers is automatically scaled to have a sensible size. If true, then the sizes of all the plotted markers are examined, and some dynamically calculated factor is applied to them all to make them a sensible size (by default, the largest ones will be a few tens of pixels). If false, the sizes will be the actual input values in units of pixels.

  If auto-scaling is off, then markers will keep exactly the same screen size during pan and zoom operations; if it's on, then the visible sizes will change according to what other points are currently plotted.

  Marker size is also affected by the `scale` parameter.

  [Default: `true`]

`icmdN = <cmds>` (ProcessingStep[])
  Specifies processing to be performed on the layer N input table as specified by parameter `inN`. The value of this parameter is one or more of the filter commands described in Section 6.1. If more than one is given, they must be separated by semicolon characters (";"). This parameter can be repeated multiple times on the same command line to build up a list of processing steps. The sequence of commands given in this way defines the processing pipeline which is performed on the table.

  Commands may alternatively be supplied in an external file, by using the indirection character '`@`'. Thus a value of "`@filename`" causes the file `filename` to be read for a list of filter commands to execute. The commands in the file may be separated by newline characters and/or semicolons, and lines which are blank or which start with a '`#`' character are ignored. A backslash character '`\`' at the end of a line joins it with the following line.

`ifmtN = <in-format>` (String)
  Specifies the format of the input table as specified by parameter `inN`. The known formats are listed in Section 5.1.1. This flag can be used if you know what format your table is in. If it has the special value `(auto)` (the default), then an attempt will be made to detect the format of the table automatically. This cannot always be done correctly however, in which case the program will exit with an error explaining which formats were attempted. This parameter is ignored for scheme-specified tables.

  [Default: `(auto)`]

`inN = <table>` (StarTable)
  The location of the input table. This may take one of the following forms:
  - A filename.
  - A URL.
  - The special value "`-`", meaning standard input. In this case the input format must be given explicitly using the `ifmtN` parameter. Note that not all formats can be streamed in this way.
  - A scheme specification of the form `:<scheme-name>:<scheme-args>`.
  - A system command line with either a "`<`" character at the start, or a "`|`" character at the end ("`<syscmd`" or "`syscmd|`"). This executes the given pipeline and reads from its standard output. This will probably only work on unix-like systems.
  In any case, compressed data in one of the supported compression formats (gzip, Unix compress or bzip2) will be decompressed transparently.
`istreamN = true|false` (Boolean)
  If set true, the input table specified by the `inN` parameter will be read as a stream. It is necessary to give the `ifmtN` parameter in this case. Depending on the required operations and processing mode, this may cause the read to fail (sometimes it is necessary to read the table more than once). It is not normally necessary to set this flag; in most cases the data will be streamed automatically if that is the best thing to do. However it can sometimes result in less resource usage when processing large files in certain formats (such as VOTable). This parameter is ignored for scheme-specified tables.

  [Default: `false`]

`scaleN = <factor>` (Double)
  Scales the size of variable-sized markers. The default is 1, smaller or larger values multiply the visible sizes accordingly.

  [Default: `1`]

`shadingN = auto|flat|translucent|transparent|density|aux|weighted <shade-paramsN>` (ShapeMode)
  Determines how plotted objects in layer N are coloured. This may be influenced by how many objects are plotted over each other as well as the values of other parameters. Available options (Section 8.4) are:
  - `auto`
  - `flat`
  - `translucent`
  - `transparent`
  - `density`
  - `aux`
  - `weighted`
  Each of these options comes with its own set of parameters to specify the details of how colouring is done.

  [Default: `auto`]

`shapeN = open_rectangle|open_triangle|...` (BasicXYShape)
  The available options are:
  - `open_rectangle`
  - `open_triangle`
  - `open_triangle_down`
  - `open_diamond`
  - `open_ellipse`
  - `filled_rectangle`
  - `filled_triangle`
  - `filled_triangle_down`
  - `filled_diamond`
  - `filled_ellipse`

  [Default: `open_rectangle`]

`thickN = <int-value>` (Integer)
  Controls the line thickness used when drawing shapes. Zero, the default value, means a 1-pixel-wide line is used. Larger values make drawn lines thicker, but note changing this value will not affect all shapes, for instance filled rectangles contain no line drawings.

  [Default: `0`]

`xsizeN = <num-expr>` (String)
  Horizontal extent of each marker. Units are pixels unless auto-scaling is in effect, in which case units are arbitrary.

  The value is a numeric algebraic expression based on column names as described in Section 10.

`ysizeN = <num-expr>` (String)
  Vertical extent of each marker. Units are pixels unless auto-scaling is in effect, in which case units are arbitrary.

  The value is a numeric algebraic expression based on column names as described in Section 10.

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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