Anatomy of a ContourPlot

Resources that control the various aspects of a contour plot relate to one of the following: the input data to be contoured, informational labels, the contouring operation, or composite objects. The ContourPlot resources description details all resources for this object. These resources can be logically reduced to the following categories:

• The input dataset to be contoured
  • The data object

    The data object associated with ContourPlot is ScalarField. The resource cnScalarFieldData specifies the id of a ScalarField data object. It must be set to create a contour plot.

  • Constant field data

    Often when the entire input dataset presented to ContourPlot is a constant value, this is an indication of a problem reading the dataset. There are about two dozen resources that allow you to configure how constant field labels appear on the plot. They begin with the prefix "cnConstF".

  • Missing data values

    NCAR Graphics utilities are written to allow for missing values in a dataset. Actions are taken to allow contouring to proceed by interpolating a value for the missing value. These resources begin with the prefix "cnMissingVal".

  • Raster contouring

    Contouring is normally done in a vector mode with polylines and filled polygons. However, contouring can also be done in raster mode with a color assigned to each cell of the two-dimensional data array based upon the data value. The resolution of the plot depends on the granularity of the data. These resources begin with a prefix of "cnRaster".

• Labels

  ContourPlot provides extreme flexibility in labeling of highs, lows, range of the data, and contouring levels. The resources that begin with the prefix "cnLabel" apply to all kinds of labels. In addition, there are resources for each of the following kinds of labels:

  • Information labels

    The information label typically states the range of data being contoured and the range of the interval between contours. These resources begin with the prefix "cnInfoLabel".

  • Labeling field highs

    The relative maxima in the data field can be printed within masked boxes. These resources begin with the prefix "cnHighLabel".

  • Labeling field lows

    The relative minima in the data field can be printed within masked boxes. These resources begin with the prefix "cnLowLabel".

  • Labeling contour lines

    The field value of individual contour lines can be labeled. These resources begin with the prefix "cnLineLabel".

• Contouring
  • Contour levels

    These controls allow you to select the number of contour levels, and the field value increment between levels. Levels can have constant spacing or be set in an explicit manner. These resources begin with a prefix of "cnMaxLevel", "cnMinLevel", "cnMonoLevel", or "cnLevel".

  • Contour lines

    Lines can be drawn at the selected contour levels. These lines can be of differing widths, dash patterns, and colors. These resources begin with a prefix of either "cnLine" or "cnMonoLine".

  • Filling contour level regions

    The regions between contour levels can be pattern-filled or color-filled. These resources begin with a prefix of either "cnFill" or "cnMonoFill".

  • Contour smoothing

    Contour lines can be smoothed for appearance. These resources begin with a prefix of "cnSmoothing".

• Composite objects

  Composite objects associated with a ContourPlot object include TickMark, LabelBar, and Legend. TickMark resources begin with the prefix "tm". LabelBar resources begin with the prefix "lb". Legend resources begin with the prefix "lg".

  • The plot boundary

    ContourPlot uses the TickMark class to set up the plot boundary, scales, tick marks, and grid; however, ContourPlot has a few resources that override the TickMark resources with respect to the grid boundary. These resources begin with the prefix "cnGridBoundPerim".

  • LabelBar ranges of filled levels

    A LabelBar showing contour level ranges is often included on contour plots that use color-filled or pattern-filled regions. In addition to the many resources of the LabelBar object, there are a couple ContourPlot resources specific to the use of a LabelBar. They are cnExplicitLabelBarLabelsOn and cnLabelBarEndLabelsOn.

  • Legend ranges of contour lines

    A Legend showing contour line values is often included on plots that do not have color-filled or pattern-filled regions. In addition to the many resources of the Legend object, there are a couple ContourPlot resources specific to the use of a Legend. They are cnExplicitLegendLabelsOn and cnLegendLevelFlags.

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