The greatest problem in real-time visualization is the large amount of data which has to be displayed in time. Therefore runtime-performance is very important . We use virtual instruments to visualize data. These instruments look like real-world instruments and so they can easily be recognized and used intuitively by the user. These virtual instruments must be able to be arranged freely and configured dynamically. In the following sections we describe the importance of regard for human perception, the displaying of old and new data at the same time, the functionality of multi-instruments and the need of scales and labels.
In real-time visualization it is very important to have regard for human perception since it is necessary that the user interprets the data correctly and recognizes critical situations in time. Therefore some special aspects of human perception should be mentioned.
The human eye focusses a round area with a limited diameter (of approximately 4 cm). So important information should be placed rather near this range . Values which are displayed left are usually estimated to be more important than those displayed right . Usually it is easier to quantify sectors of the full circle than portions of a bar. . Pictures are recognized faster and more easily than alphanumerics . The colors used by the system have to be chosen very carefully. They must guaranty the best perception. So the saturation must not be to high and they must differ in hue from each other as much as possible.
We call the values which have occured some time
before the history of a value. These older values are of great
interest because you can recognize changes and trends. We used
rectangles resp. triangles which fade to the background for
displaying those histories.
So the display colors must have enough saturation for displaying older values in colors fading to the background color.
One of the features is the possibility to create multi-instruments. Those multi-instruments are designed to visualize different values at the same time. Those multi-instruments are necessary for comparing values especially in redundant systems.
Whenever important information has to be visualized, using redundant display methods are a good idea to help the user interpreting the visualized information correctly. So redundant visualization should be done whereever it does not waste too much space. For this reason we used color-assignment for showing which numeric displays are belonging to which value.
Because the values change fast, the user is not able to read each
value on a numeric display. The display technics of virtual
instruments like needles or bars can be followed fast by the user
but they give no exact representation of the value. So the user
needs more help in form of a grid or scale to read the exact value
from needles or bars also.
Those scales have minor lines and major lines. Major lines are a little bit longer than minor lines and have a label showing the numeric value.
Because of the small focus of the human eye we decided to display numeric values nearby the moving display item, for example at the end of the needle of a gauge.
But if the needle moves too fast the user is unable to read the ''jumping'' numeric display. So we tried to find a compromise between readability and correct position. Now we calculate a slower movement, which means less positions per time, for the moving numeric displays.
The developed algorithm covers also another problem, the problem of overlapping displays. Now the numeric displays are arranged in a manner, that they do not overlap and not move too fast or too frequent.
In real time applications values often have ranges, which should not be reached during normal operation. If these red ranges are reached, the user has to recognize this immediately. Therefore these ranges must be represented in a special manner.
Similar to the red ranges described above there are also hard
limits. These hard limit are values which cannot be reached
when the system is working correctly. If they are reached there
is a system-failure or a misconfiguration of the system.
If those hard limits are overrided, the user gets a warning and a special sign on the instrument where the value should be displayed.
The interaction with visualization software for real-time data has to be intuitive, because the user has no possibility to stop the application for reading instructions or even a manual. Because of this reason, also all configuration must be able to be done at run-time.