Note: The Contours panel is a new feature of VAPOR 2.4, it was not available in VAPOR 2.3.
A contour line is a curve (or set of curves) in a planar region that traces the points where a variable has a particular value. The variable value on the contour line is referred to as the “isovalue”. The VAPOR contour line renderer will display contour lines of either two-dimensional or three-dimensional variables. When the variables are 2-D, the contour lines are displayed in a horizontal plane. When the variables are 3-D, the contour lines are displayed in an arbitrarily oriented planar slice. The user may select any number of isovalues to be displayed. A color mapping is provided to support coloring contour lines according to their isovalue. The contour lines can also be annotated with text indicating the isovalue. The constructed contour lines can also be visualized in either the Probe or 2D panel as the boundaries between different color bands.
The Contour Lines panel provides several different ways of specifying the isovalues, in the section labeled “IsoValue Selection”.
This panel (in the Basic Settings) is similar to a transfer function editor or to the Iso selection window in the Isosurface panel. A histogram of variable values is displayed alongside the isovalues. A color bar is provided that can be used to color the contour lines (if “Use single color” is not checked under Contour Line Appearance). Modifying the left or right bound of the histogram will also change the isovalues if they are not between the left and right histogram bounds.
The IsoValue selection window includes a button labeled “Copy to 2D” (when the variable is 2D) or “Copy to Probe” (when the variable is 3D). When this button is clicked, the transfer function in the currently active 2D or Probe instance, for the current contour variable, is modified so that the 2D or Probe instance will display the contour lines as boundaries between color bands. The transfer function of the contour variable (in either the 2D or Probe panel) is modified so that the color changes in the transfer function occur at the specified isovalues, and the colors are constant between those values. This copy does not change the contour line panel settings. Prior to clicking this button, you may want to check the current transfer function for the contour variable in the Probe or 2D tab, to make sure that transfer function is the one you want to use for coloring the contours.
The contour line layout section depends on whether the variable is 2D or 3D. When the variable is 3D, the contour line layout window is the same as the layout section of the Probe tab, allowing specification of an arbitrarily oriented rectangle in the scene. When the variable is 2D, the contour line layout section is similar to the layout section of the 2D panel, allowing specification of a horizontal axis-aligned rectangle. The shape and size of the contour line rectangle can also be visually adjusted using the contours manipulation mode, from the manipulation mode selector.
Starting with VAPOR 2.5, contour lines can be displaced vertically to match the terrain height when the contour variable is 2D. Users must specify a 2D height variable that prescribes the terrain height, and check the "Apply to terrain" check box in the contour layout section.
The contour line image panel displays the contour lines in a 2D window. Users can control the background color and line width using the button and text box immediately below the image. Below the image is a section entitled “Cursor (cross-hair) Selection and Usage”. This is used for point selection, so that users can query the coordinates of particular points near the contour lines and the variable values at these points. In Contours mode, the 3D coordinates of the selected point are displayed as 3D cross-hairs in the 3D scene. The selected point can also be used to specify flow seed points in the same manner as these are specified in the Probe and 2D panels.
The appearance section of the Contours panel provides control of the line width, color, and annotation. When the “Use Single Color” is un-checked, the line colors are determined by the color mapping in the isovalue selection window in the basic settings. When checked, the single color is specified by clicking the “Select” button in the Appearance settings. To enable text annotation, click on the “Show Text” check box, and specify a text density between 0 and 1, determining how frequently the text will appear along the length of a contour line. The number of digits displayed and the text size are also set in this section.
Starting with VAPOR 2.5, the text labels can be displayed in one of three ways, based on the selected "Text Label Type":
