3.2 Java1492-plotting large quantities of data using java  (Page 4/27)

Two overloaded constructors

Two overloaded constructors are provided for the class. One constructor plots the data using a set of default plotting parameters. This constructor isprovided for extreme ease of use. The only information that you must provide to this constructor is a string that becomes part of the title for each page.

(The pages in Figure 1 were plotted using default plotting parameters with a title string of "B". The amount of data that was fed to the plottingobject for Figure 1 filled Page 0 and almost filled Page 1.)

Can change default plotting parameters

I coded the values of the default plotting parameters to make the results suitable for use in this narrow publication format. If you don't like my choiceof default plotting parameters, you can change them to values that you find more useful. For example, you could cause the default size of the Frame object to fill your screen, allowing you to plot quite a lot of data on eachpage.

Control over the plotting parameters

The other overloaded constructor takes seven parameters that allow you to control all aspects of the plotting format including:

• Page title
• Frame width and hence plotted data width
• Frame height, spacing between traces, and hence the number of traces per page
• Spacing between samples, number of traces per page, and hence the number of samples per page
• Width and height of an oval that is used to mark each sample on the plot

The plotted sample values are connected by a straight line. Each sample is marked with an oval. You can specify the width and the height of the oval inpixels. If you set the width and height to zero, the oval simply disappears from the plot.

Default plotting parameters in Figure 1

The plots in Figure 1 were produced using the constructor that applies default plotting parameters. For example, the data was plotted using the defaultvalue of two pixels per sample. Hence the lines connecting the sample values in Figure 1 are very short.

The ovals in Figure 1 had a default width and height of two pixels each. At this small size, the ovals end up looking more like plus characters than ovals.

The overall parameters governing the plot in Figure 1 were:

Explanation of terms

Some explanation of the terminology in the above list is probably in order. The Frame width and Frame height are the actual width and height of the Frame objects shown in Figure 1 .

The Page width and Page height are the width and height of a Canvas object contained in the Frame object, upon which the plotting is performed. The width of the Canvas actually controls the number of samples that can be plotted in each trace.

The Trace spacing is the number of pixels that separate each of the horizontal axes on a page in Figure 1 .

The Sample spacing specifies the number of pixels that are dedicated to each sample horizontally. In Figure 1 , that value is 2. This means that every other black pixel in Figure 1 indicates the value of a data sample. The pixels in between are fillers.