Contours

The scalar values in a data set represent a sampling of values from a continuous function. Contour lines of constant value created by interpolating the sample values are very useful when visualizing this function. SMS uses linear interpolation across the elements, triangles or grid cells to generate these contours. Contour display is enabled using in the Display Options dialog of each applicable module.

The options used to generate contours can be edited by selecting the Contour Options command in the Data menu or by selecting the Contour Options button in either the Data Browser or Display Options dialogs. The values in the upper left corner of the dialog correspond to the maximum and minimum values in the active data sets active timestep. These values are sometimes useful when choosing an appropriate contour interval.

The number of contours is user controlled. Options include the specification of a number of contour intervals, a specified contour interval, or a set of explicit contour values. For either a specified interval or specified number of contours options, a maximum and a minimum contour value can be specified and the contouring can be restricted to this specified range. If no explicit range is specified, SMS will choose a range to optimize the color distribution inside the extreme values for the data set. If the Values button is selected, the Contour Values dialog is displayed. Up to ten specific contour values can be typed into the dialog.

The items in the upper right section of the Contour Options dialog control the display of a contour legend and the option to accentuate some of the contours. If the Show color legend option is selected, and the contours are not being displayed as a single color, a legend of colors and corresponding data set values is displayed in a corner of Graphics Window. For color filled contours, this legend is a vertical strip of colors with text labels for the contour levels. If the contours are being displayed as linear segments or cubic splines, the legend is displayed as a series of contour level values and a line drawn in the color corresponding to that level. The size, location, label and font for the legend are set using the Legend Options dialog. If the user enters the title "DS" for the legend title, the name of the current data set is used. If the user enters "DS:TS" the current dataset and timestep are used as the title.

The options in the middle of the right side of the dialog control how the contours are computed and displayed. Three contouring methods are available:

• The default method is Normal Linear Contours and causes the contours to be displayed as piece-wise linear strings.

• If using the Color fill between contours method, the same linear contour strings are computed, but the regions between adjacent contour lines is filled with a solid color.

• ·If using the Cubic Spline Contours method, the contours are computed in strings and drawn as cubic splines. Drawing the contours as splines can cause the contours to appear smoother. Occasionally, loops appear in the splines or the splines cross neighboring contour splines. These problems can sometimes be fixed by adding tension to the splines. A tension factor greater than zero causes the cubic spline to be blended with or converge to a linear spline based on the same set of points. A tension factor of unity causes the cubic spline to coincide with the linear spline.

In the lower right corner of the Contour Options dialog, two buttons allow the user to specify the contour colors and the contour labeling options.

Related Topics
Contour Labels
Color Ramps