Using a Plot to draw text involves supplying a string of text to be displayed and a position in physical coordinates where the text is to appear. The position is transformed into graphical coordinates to determine where the text should appear on the plotting surface. You must also provide a 2-element UP vector which gives the upward direction of the text in graphical coordinates. This allows text to be drawn at any angle.
Plotting is performed by AST_TEXT, for example:
CHARACTER * ( 20 ) TEXT DOUBLE PRECISION POS( NCOORD ) REAL UP( 2 ) DATA UP / 0.0, 1.0 / ... CALL AST_TEXT( PLOT, TEXT, POS, UP, 'TL', STATUS )
Here, TEXT contains the string to be drawn, POS is an array of physical coordinates and UP specifies the upward vector. In this case, the text will be drawn horizontally. The penultimate argument specifies the text justification, here indicating that the top left corner of the text should appear at the position given.
Further control over the appearance of the text is possible by setting
values for various Plot attributes, for example Colour, Font and Size.
Sub-strings within the displayed text can be given different appearances,
or turned into super-scripts or sub-scripts, by the inclusion of escape
sequences (see section ) within the supplied text string.
AST A Library for Handling World Coordinate Systems in Astronomy