1.  Programming Interface

    Application programs can send data and set the appearance of the graph.  Programming interfaces for different languages are available:

1.1 Developing Applets with ElVis

    Java applets can incorporate ElVis graphs.  The classes for creating graphs are in elvis.jar.  The applet and its classes can be stored in a separate .jar file.  The applet is launched from an HTML file such as:
<applet code="EApplet.class"
        archive="eapplet.jar, elvis.jar"
        width="1024" height="768">
<param name="type" value="application/x-java-bean;version=1.3">
A sample applet is in EApplet.java and archived in eapplet.jar.

2.  Graph Components

Image of graph

    The elements of a graph are shown in the diagram above.  The graph contains:     The coordinate system of the graph has its origin (0., 0.) at the lower left corner.  The coordinates of the upper right corner are (1., 1.).  The location and size of elements, including the height of text labels, is specified in this coordinate system.  All the elements scale continuously and uniformly when the size of the graph is changed.

    The default layout for a graph is shown in the diagram above.  The axes labels, title, and index label are automatically drawn if the application program specifies a text string.  If no string is specified then no text is drawn.  Additional labels can be drawn anywhere within the graph.  Labels are clipped to the edges of the graph.  Portions of a label that extend beyond an edge of the graph are not seen.

Plot Area

    The size and location of the plot area can be controlled through the API.   The default plot area shown in the diagram  is used if the application does not specify a plot area.  

    The datasets are drawn within the plot area.  A dataset is equivalent to a "function" in a "multigraph" drawn by the rplot program.  A graph contains one or more datasets.  Each dataset is drawn in a different color.  Markers can be drawn at the location of data points.  When datasets are not indexed they are all drawn in the plot area at the same time.

    A dataset represents a function at a specific index value.  For time indexed data, the function at each time step is added to the graph as a separate indexed dataset.  If the datasets are indexed in time or some other variable then only the dataset for the current index value is drawn.  Each indexed dataset is drawn with the same color.   The datasets are displayed sequentially or animated continuously in index order.  The user interface has controls for incrementing or decrementing the index value and animating the playback.

X Axis, Y Axis

    The X axis is drawn along the bottom of the graph.  A label is automatically drawn below the numbers.

    The Y axis is drawn along the left edge of the graph.  A label is automatically drawn to the left of the numbers.

  Major ticks and minor ticks are automatically drawn along the axis based on the range of the data.  The tick locations are computed in ElVis so the tick numbers increment equally.  Tick numbers contain up to 3 digits, a decimal point, and a negative sign when needed.  If all the numbers for an axis can be represented in 3 digits then algebraic numbering style is used.  If not, then the numbers are automatically shown in scientific notation.  The mantissa is drawn next to the major tick and the exponent string is appended to the axis label.  There is an option to draw grid lines across the graph at major tick locations.

    The application program can set the spacing of the ticks to be linear or logarithmic.   The default is linear.


    A title label is automatically positioned below the plot area.

Index Label

    Datasets can be indexed by time or a user specified quantity. Indexed datasets are displayed sequentially or animated continuously.  The index number is drawn along with the specified text.

Text Labels

    Additional labels can be drawn anywhere in the graph.  The application sets the location color, font, style, and size of the label.  The figure below shows fonts and styles that are available.

Image of fonts


    A legend is drawn when 2 or more datasets are plotted.  Each entry in the legend contains the name of the dataset and the style and color of its plot.

3.  GraphWindow

    Graphs are located within GraphWindows.  A GraphWindow contains a grid of graphs.  Each grid cell contains 1 graph as shown in the figure below.

Image of GraphWindow

    A GraphWindow has horizontal and vertical scrollbars when the grid is bigger than the window.  Dragging the right edge of column changes the width of the column.  Dragging the bottom edge of a row changes the height of a row.  Dragging the lower right corner of a cell with mouse button 1 changes the column width and row height.  Dragging the corner with mouse button 3 maintains the aspect ratio of the graph in the cell.  The aspect ratio of other cells will change however.

    The entire grid of graphs is shown when the window is initially displayed.  The menubar items for a GraphWindow are:
        Window-->Fit Scope Panel  -  All of the graphs are shown, maintaining aspect ratio.
        Window-->Fit Graph  -  The graphs are resized so the upper left graph fills the window.
        Window-->Fill Graphs  -  All of the graphs are shown and fill the window.
        Window-->Print  -  A PostScript file is created for each graph.
        Window-->Close All  -  All of the GraphWindows are removed.

    The <----|----> button in the menubar resizes all the graphs in a window.  Clicking on the right half of the button enlarges the graphs, while clicking on the left half shrinks the graphs.  The magnitude of the size change is proportional to the horizontal distance from the center of the button.

    GraphWindows are automatically tiled as they are added to the desktop window.

4.  Interactive Features

4.1 Data Examination

4.1.1  Zoom and Translate the Data

    The data drawn within the plot area can be examined by zooming in.  Drawing a  zoom rectangle  with mouse button 1 (MB1) will set the zoom area.  Press MB1 within the plot area to set one corner of the rectangle and drag the cursor to the opposite corner.  The zoom rectangle is drawn while maintaining the aspect ratio of the plot area.  Releasing MB1 applies the zoom.

    Hold down the Ctrl key and press MB1 to start a rectangle that will zoom out on the data.

    Typing the = key zooms in.  (The = key increases the zoom and is a convenience for typing + to increase the zoom.)

    Typing the - key zooms out.

    The 4 arrow keys translate the view of the data.  Move the cursor into the desired graph.  Type the left, right, up, or down arrow keys to translate the view of the data.

    The view of the data can be reset from the menubar:  Graph-->Reset View.

    The view of the selected graph can be applied to all graphs in the GraphWindow from the menubar:  Graph-->Apply Scale All.

4.1.2  Display Data Values

To display data values, press MB1 above or below the plot area.  This will draw a vertical dashed line and display the X value for that location in the data.  A horizontal, color-coded dashed line will be drawn for each intersecting dataset.  The Y value of the dataset will be displayed.

The data values will be displayed for each graph in the selected GraphWindow.  The graphs can be have different zoom and translations.

The data values for indexed graphs can also be displayed while the datasets are being animated.

4.2 Surface Plots

There are keyboard shortcuts for viewing options of surface plots:

Letter       Action
a                Draw lines, shaded polygons, and centroids.
f                 Draw shaded polygons and the line segments of each data set in the surface.
l                 Draw polygon outlines and centroids.
p                Draw shaded polygons (default setting).
u                Toggles culling of back-facing polygons.  Turn off culling to see polygons from behind or below the surface.
w                Draw polygon outlines only.
/                  Each / draws a polygon in depth order.  Type 0 to erase all; type 9 to display all.

5.  Load gnuplot Files, Plots from Columns of Data

ElVis can display a graph from a gnuplot command file containing "plot" commands.  The plot command references a text file containing 2 or more columns of values.  An example for the plot command in a command file is:

plot "sim.dat"  using 2:3  title "Simulation of Electron Density"

The filename is required and enclosed in quotation marks. The filename is the first word after the plot command.   Each line in this text file contains 2 or more values, forming columns of data.  Any column can be used for either the X or Y values.  The column assignment is specified after the keyword using.  The example specifies column 2 as the X values and column 3 as the Y values.  If no column assignment is made then column 1 is read as the X values and column 2 is read as the Y values.  The title of the graph is (optionally) specified after the keyword title. The title can be one or more words enclosed in quotation marks.

Multiple datasets can be plotted on one graph by having multiple plot commands in the file.  Each plot command should be on a separate line in the command file.  Alternatively, a plot command can have more than one file by using a comma as a separator:

plot "sim.dat" using 2:3, "exp.dat" title "Comparison"

The command can continue on more than one line by ending each line with \ as shown:

plot "sim.dat" using 2:3, \
   "exp.dat" title "Comparison"


The commands for setting the X and Y axis labels are:

set xlabel "Your X Label"
set ylabel "Your Y Label"

Blank lines and comment lines starting with # are ignored.  For compatibility with the gnuplot parser, a style can be included after the keyword using, such as: using 1:4 with lines, but it is ignored when read into ElVis.  The GraphEditor can be used to display lines or points in a graph.

The command file is accessed from the menubar:  File-->Load File.  This brings up a file selection box.  Set the Files of Type to gnuplot files.  All files except *.gw, *.nc, and *.cdf will be listed.