Color gradients

Syntax: DENSITY { x y } z { p1 p2 }
Qualifiers: \LEGEND, \HISTOGRAM, \PARTIAL, \XPROFILE, \YPROFILE, \BORDER, \AXES, \RESET
Defaults: if z is a matrix: x=[1;2;3;...], y=[1;2;3;...], p1 = 0, p2 = 1, \LINEAR, \-PARTIAL, \-XPROFILE, \-YPROFILE, \BORDER, \AXES, \RESET

Color gradients is the default density type. No qualifiers are needed to produce this type of drawing. The range of values of the matrix is divided into ten (10) equal levels, and a different color is associated with each level. By default, a value is interpolated at each pixel location within the matrix region so as to give smoothly joined regions.

Input variables

If z is a vector, the parameters x and y are expected and must be vectors. x and y are assumed to represent a scattered set of points, where z[i] is the altitude corresponding to the location (x[i],y[i]). A matrix is interpolated on these scattered points by means of a Thiessen triangulation of the plane. The three vectors must be the same length.

If z is a matrix, the parameters x and y default to [1;2;3;...], but if entered they must be vectors. Each matrix element, z[i,j], is associated with the coordinates (x[j],y[i]). The length of x must be equal to the number of columns of z and the length of y must be equal to the number of rows. The vectors x and y are used for scaling the axes.

Not interpolated gradients

If the \HISTOGRAM qualifier is used, each data location is represented by a rectangle of color, centered on the data location. The regions are not smoothly joined.

Changing the range of values

The optional parameters p1 and p2 can be used to broaden or shrink the range of data values. If zmax is the maximum value of the data and zmin is the minimum value of the data, the full color range will be from a minimum of p1*(zmax-zmin)+zmin to a maximum of p2*(zmax-zmin)+zmin. If z is a data value and if z < p1*(zmax-zmin)+zmin, that data value is treated as zmin. If z > p1*(zmax-zmin)+zmin, that data value is treated as zmax. The default values are: p1=0 and p2=1.

Legend

If the \LEGEND qualifier is used, a legend is drawn along the right side of the axes. The legend requires the right end of the x-axis to be set to 75% of the window, that is, XUPPERAXIS is set to 75%.

When a y-profile is drawn, using the \YPROFILE qualifier, the right edge of the axis box must allow space for the profile as well as a possible legend. If a y-legend profile and a legend are present, then XUPPERAXIS is set to 65%. If a y-legend profile is present but not a legend, then XUPPERAXIS is set to 85%.

By default, XUPPERAXIS is reset to its former value after the DENSITY command. If the /-RESET qualifier is used, the axis location is not reset.

Examples

These examples use the following vectors.

 X=[  1;  0;  1;  0;   .2; .3;   .5;  .8]
 Y=[  5;  5;  0;  0;    1;1.5;  2.5;   4]
 Z=[ 10; 10; 10; 10; -100; 10; -100; 500]
 

SET COLORMAP THERMAL
DENSITY\LEGEND X Y Z

SET COLORMAP RAINBOW
DENSITY\LEGEND X Y Z

  DENSITY command
  DITHERING