A symbol object represents a graphical element that is plotted relative to a particular position.

Note: IDL provides many predefined symbols. See Formatting IDL Colors, Graphics Symbols, and Lines for more information on the symbols available.




See IDLgrSymbol::Init.


Objects of this class have the following properties. See IDLgrSymbol Properties for details on individual properties.


This class has the following methods:

In addition, this class inherits the methods of its superclasses (if any).


Creating Symbol Objects

Specify the type of symbol to use when you call the IDLgrSymbol::Init method.

To Use a Pre-defined Symbol

To create a symbol object using a red triangle (symbol index 5), use the following statement:

mySymbol = OBJ_NEW('IDLgrSymbol', 5, COLOR=[255,0,0])

See IDLgrSymbol Properties for a list of available symbol values.

To Use a Graphic Object as a Symbol

You can use an visualization object or a model object as a symbol. For best results, create an object that fills the domain between –1 and 1 in all directions. For example, the following statements create a polygon object in the shape of a pentagon and define a symbol object to use the polygon:

pentagon=OBJ_NEW('IDLgrPolygon', [-0.8,0.0,0.8,0.4,-0.4], $
    [0.2,0.8,0.2,-0.8,-0.8], COLOR=[0,0,255])
mySymbol = OBJ_NEW('IDLgrSymbol', pentagon)

Note that we create the pentagon to fit in the plane between –1 and 1 in both the X and Y directions. We could also have created the pentagon to fit in a unit square and then scaled it to fit the domain between –1 and 1.

For example:

pentagon=OBJ_NEW('IDLgrPolygon', [0.1,0.5,0.9,0.7,0.3], $
   [0.6,0.9,0.6,0.1,0.1], COLOR=[0,0,255])
symModel = OBJ_NEW('IDLgrModel')
symModel->Add, pentagon
symModel->Scale, 2, 2, 1
symModel->Translate, -1, -1, 0
mySymbol = OBJ_NEW('IDLgrSymbol', symModel)

Note: We create the symbol object to use the model object rather than the polygon object. Using a model object as a symbol allows you to apply transformations to the symbol even after it has been created.

Setting Size

By default, symbols extend one unit to each side of the data point they represent. Set the SIZE property of the symbol object to a two-element vector that describes the scaling factor in X and Y to apply to the symbol to change the size of the symbols that are rendered. For example, to scale a symbol so that it extends 1/10 of a unit to each side of the data point, use the statement:

mySymbol->SetProperty, SIZE=[0.1, 0.1]

Setting Color

If you are using a pre-defined symbol, you can set its color using the COLOR property of the symbol object. If you are using a graphic object as a symbol, the symbol’s color is determined by the color of the graphic object and the setting of the COLOR property of the symbol object itself is ignored. For example, the following statement creates a symbol object that uses a red triangle:

mySymbol = OBJ_NEW('IDLgrSymbol', 5, COLOR=[255,0,0])

Version History




Added ALPHA_CHANNEL property


Added NAME and UVALUE properties


Added ANTIALIAS, FILL_COLOR, and FILLED properties