3.1 Java1489-plotting 3d surfaces using java  (Page 4/24)

A calibration scale

Each of the images in Figure 1 shows a calibration scale immediately below the image of the surface. The calibration scale shows the color or shade of grayused to represent each elevation on the surface. The color or shade of the lowest elevation is shown on the left of the scale and the color or shade of thehighest elevation is shown on the right.

For example, the scale on the Grayscale image shows a smooth gradient from black to white going from left to right. The shade of gray shown at the midpointon the calibration scale represents the elevation that is halfway between the lowest elevation and the highest elevation.

Color Shift plot

The image in the center in Figure 1 shows the same surface plotted using a smooth gradient from blue at the low end through aqua, green, and yellow to redat the high end. In addition, this plotting format sets the lowest elevation to black and the highest elevation to white so that these two elevations areobvious in the plot.

(The highest elevation was indicated by a small white square at the center in the original program output, and the lowest elevations wereindicated by the black areas near the corners. However, the small white square seems to have faded away in the published version of this plot.)

More information is conveyed

This plotting format can convey a great deal more information to a human observer than the Grayscale plotting format. This is because the human eye candiscern more different colors than it can discern different shades of gray.

(Many years ago, when I was in the SONAR business, the general rule of thumb was that a typical human can discern only about seven shades ofgray from black to white inclusive. Obviously a typical human can discern more than seven different colors.)

The lowest elevations are obvious in the color shift plot

By using black to indicate the lowest elevation, (in addition to using shades of blue to indicate low elevations) , it is easy to determine the exact locations of the lowest elevations in the Color Shift plot in the centerof Figure 1 . On the other hand, the locations of the lowest elevations are not discernable in the Grayscale plot at the left Figure 1 .

Four minor peaks are obvious in the color shift plot

Also, it is obvious from the Color Shift plot that the surface has four minor peaks at the edges of the plot. Although the Grayscale plot has a slight hint ofthose minor peaks, they are certainly not obvious.

By comparing the color at the top of the minor peaks to the color scale below the Color Shift surface, it is possible to estimate that the elevation of theminor peaks is probably somewhere between twenty-five and fifty percent of the elevation of the main central peak. It is clearly impossible to glean that kindof information from the Grayscale plot of the same surface.

The highest elevation is obvious in the color shift plot

Although no longer true in this reproduction of the original computer output, by using white to indicate the highest elevation (in addition to using shades of red to indicate high elevations) , it is easy to determine the exact location of the highest elevation in the Color Shift plot. As explainedearlier, the highest elevation was indicated by a small white square, which was on the cross hairs at the center of the original plot.