CONTOUR2 Procedure

Draws a contour plot from data stored in an array.

Usage

CONTOUR2, z[, x, y]

Input Parameters

z—A 1D or 2D array containing values of the dependent variable z=z(x, y).

x—A 1D or 2D array containing values of the first independent variable. If z is 1D, then x is a required 1D input variable with the same number of elements as z. If z is 2D, then x is an optional 1D or 2D input.

y—A 1D or 2D array containing values of the second independent variable. If z is 1D, then y is a required 1D input variable with the same number of elements as z. If z is 2D, then y is an optional 1D or 2D input.

Keywords

C_Fillcolors—Specifies an array of color indices used to fill the contour intervals.

Fill—Fills contour intervals with color. This keyword can have the following values:

0—No fill (Default)
1—Filled intervals with contour lines
2—Filled intervals with no contour lines

Note: If Fill is specified, labeling is disabled. See Example 2 for information on creating a filled contour plot with labels.

Frequency—A floating-point value > 0.0 that determines how frequently labels are printed along the contour. If z is an m-by-n array, the default Frequency value is: MIN(m,n)/3.5. If z is a 1D array of length m, the default Frequency value is: SQRT(m)/3.5.

Label_style—An integer specifying the contour label fill style. Possible values are:

0—Do not print labels (Default)
1—Print labels and fill them with the background color. This option takes effect if any other contour label keywords are specified (C_Annotation, C_Charsize, C_Labels, C_Charthick, Frequency).
2—Print labels with a transparent background.
3—Print labels with the fill colors specified by C_Fillcolors.

The CONTOUR2 keywords let you control many aspects of the contour plot’s appearance. For a description of each keyword, see Graphics and Plotting Keywords.

Background	Data	Subtitle	[XYZ]Tickformat
Channel	Device	T3d	[XYZ]Ticklen
Charsize	Font	Thick	[XYZ]Tickname
Charthick	Gridstyle	Tickformat	[XYZ]Ticks
Clip	Levels	Ticklen	[XYZ]Tickv
Color	Max_Value	Title	[XYZ]Title
C_Annotation	NLevels	[XYZ]Charsize	[XYZ]Type
C_Charsize	Noclip	[XYZ]Gridstyle	YLabelCenter
C_Charthick	Nodata	[XYZ]Margin	ZAxis
C_Colors	Noerase	[XYZ]Minor	ZValue
C_Labels	Normal	[XYZ]Range
C_Linestyle	Overplot	[XYZ]Style
C_Thick	Position	[XYZ]Thick

Discussion

CONTOUR2 is an implementation of an algorithm developed by Dr. Albrecht Preusser, "Computing area filling contours for surfaces defined by piecewise polynomials", Computer Aided Geometric Design 3 (1986), pp. 267-279.

CONTOUR2 provides functionality that CONTOUR does not. CONTOUR accepts only gridded data: the x and y arrays must define a curvilinear coordinate system. CONTOUR2 places no such restriction on x and y, and thus accepts scattered data as well as gridded data.

For scattered data z, x, and y are 1D arrays of the same length.

For gridded data z is a 2D (m by n) array, while x and y can be 2D, 1D, or undefined. If x and y are 2D then they are of dimensions m by n, and z(i,j) corresponds to the point ( x(i,j), y(i,j) ). If x and y are 1D then they are of lengths m and n respectively, and z(i,j) corresponds to the point ( x(i), y(j) ). If x and y are undefined then they default to x = FINDGEN(m) and y = FINDGEN(n).

Example 1

In the example below, randomly scattered data is contoured as shown in Contour Plot of Randomly Scattered Data.

seed0 = 0 & seed1 = 2 & seed2 = 5
z = RANDOMU(seed0, 20)
x = RANDOMU(seed1, 20)
y = RANDOMU(seed2, 20)
CONTOUR2, z, x, y, Nlevels=10, /XStyle, /YStyle

Contour Plot of Randomly Scattered Data

Example 2

In this example, a filled contour plot with labels is plotted as shown in Contour Plot with Labels and Fill Color. Labeling is not active for filled plots, so we’ll generate the filled plot first, then plot the contour lines with labels over the filled plot using the NoErase keyword. We’ll slightly enlarge the size and thickness of the contour labels without affecting the axis text by using the C_Charsize and C_Charthick keywords.

; Define a color table. 
TEK_COLOR
z = DIST(5)
colorindex=[20, 21, 22]
; Generate a filled plot with no contour lines.
CONTOUR2, z, /XStyle, /YStyle, NLevels=5, Fill=2, $
   C_Fillcolors=colorindex
; Fill contour labels with colors defined in colorindex array.
CONTOUR2, z, /XStyle, /YStyle, NLevels=5, Label_style=3, $
   /NoErase, C_Colors=0, C_Fillcolors=colorindex, $
   C_Charsize=1, C_Charthick=1

Contour Plot with Labels and Fill Color