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10.The Graphical Display of Data10.1.INTRODUCTION TO GRAPHS

Specifying a Coordinate System

picBox.Scale (a,d) - (b,c) : specifies x-axis range from a to b, and y-axis range from c to d.

The ordered pair (a,d) gives the coordinates of the top left corner of the picture box.

The ordered pair (b,c) gives the coordinates of the lower right corner of the picture box.

Graphics Methods for Drawing Lines, Points, and Circles

picBox.Line (x1,y1) - (x2,y2) : draws line segment from (x1,y1) to (x2,y2) in picture box.

picBox.PSet(x,y) : plots the point (x,y).

picBox.Circle(x,y),r : draws the circle with center (x,y) and radius r(in x axis units).

Positioning Text

A picture box has two properties (CurrentX, CurrentY) and two methods

(TextHeight,TextWidth) that allow us to precisely position text alongside graphics.

CurrentXand CurrentYrecord the precise horizontal and vertical location at which the next

character will be printed.

CurrentYis the location for the top of the character cursor.

Obtaining a good range of values for a graph with only positive values

picOutput.Scale (-0.2 * r, 1.2 * h) - (1.2 *r, -0.2 * h)

where r = x coordinate of the rightmost point to be drawn, h = y coordinate of the highest point to be

drawn.

Line clipping

If one or more points in a graphics method fall outside the picture box part of the line is clipped.

More than one Scale statements

A program can execute a picOutput.Scale statement more than once.

The new statements have no effect on text and graphs already drawn; however, future graphics

statements will use the new coordinate system.

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Producing colorful displays

To draw lines, points, and circles in color place a vbColorconstant at the end of the corresponding

command.

Example:picBox.Line (x1,y1) - (x2,y2), vbRed

10.2.LINE CHARTS

Line charts (x-y plots) represent y = f(x) as lines and data points.

Use labels for the axes and plot. Describe legend to identify more than one curve if needed.

See examples in section 10.2 of the textbook.

Line Styling

Use the statementpicBox.DrawStyle = s

to select different line styles

s = 0 ______________________ s = 3 - -- - -- - -- - -- - -- - -- - --

s = 1 _ _ _ _ _ _ _ _ _ _ _ s = 4 - - --- - - --- - - --- - - --- - -

s = 2 - - - - - - - - - - - - - -

10.3. BAR CHARTS

Bar charts (e.g., histograms, etc.) are produced by drawing rectangles using a variation of the line

statement.

picBox.Line (x1,y1) - (x2,y2), , B: produces a blank rectangle.

picBox.Line (x1,y1) - (x2,y2), , BF: produces a filled rectangle.

10.4. PIE CHARTS

Pie charts are produced by drawing circular sectors using the Circle and Line statements.

Let c = 2be the circumference of a unit circle, and let 0< a < b < 1, then the statement

picBox.Circle (x,y), r, , a * c, b * c

plots the circular arc limited by the angles a*c = 2a, and b*c = 2b.

Also, the statement

picBox.Circle (x,y), r, , - a * c, - b * c

plots the circular sector limited by the angles a*c = 2a, and b*c = 2b. Note: when a = 0, then the

radius corresponding to that point is not plotted. To avoid this problem use a = 0.000001, rather than a = 0.

Use the FillStyle property to fill the circular sector. See Figure 10.28 for different styles.

Use the statement picBox.FillColor = vbColor(a vbColor constant) for colorful sectors.