Angles Of View

After we have come to understand that deciphering information when it is projected is very much more difficult than comprehending its printed version, we want next to discover whether there are techniques and guidelines which, if carefully observed, can combine to minimize the substantial difficulties inherent in

Reading Displays - the Joy of Looking

Consider the following scenario:

The operators of an offshore oil drilling rig somewhere in the North Sea rely heavily on data delivered to them through an elaborate command-and-control room which consists principally of 12 rear projection screens set into a single wall and arrayed in a 2-over-6 configuration.

Monitoring systems throughout the structure feed to this room where corrective measures may be taken when or if any malfunction occurs. Data projected through the screens are, therefore, being updated continuously and in real time. Changes in those data must be recognized by the systems’ operators who are also obliged to assess those changes in real time.

Although the room is certainly manned by well more than a single operator, each operator will nevertheless be assigned to oversee some subset of screens as his specific area of responsibility. Watching and watching over this multi-image display will be the operator’s principle visual task and detecting and correctly interpreting fluctuations in the projected data will be his primary responsibility.

If we quite reasonably suppose that any single operator will not be expected to monitor a screen matrix that is greater than 2-over-2, we can still quickly see that his ability to assimilate data from any one of the four screens under his purview may not be at all equal to his capacity accurately to read the other three.

How far, for instance, should he be positioned away from the bottom two screens? At what vertical angle should he be positioned to the pair of top screens? For that matter, how big should each screen itself be? And how bright should be its imagery?

To continue with just a few obvious questions about the content of the display(s), how will we establish character size, color palette, and font? What can or what should our line frequency be? And if some of the "characters" aren’t characters but are instead symbols, how then should we proceed? And, lastly, a question we can probably answer: What happens if we choose wrong answers to some of these design questions and then, in operation, something goes wrong?

While, indeed, this may be a plausible premise for a Hollywood techno-thriller, it is also an absolutely credible real world possibility whose outcome might not actually be a fully cinematic disaster but which could definitely be both expensive and regrettable. Even for single screen displays where the intention is neither to command nor to control, these are issues and parameters about which far too little is known. Yet both the integrators and users of all such systems rarely take the time to design or analyze them according to the metrics of intelligibility.

What are those metrics and where are they to be found are not at all easy questions to answer. In preparing this article, its author spent weeks searching the literature both on-line and off and with one notable exception was unable to unearth any definitive syllabus. It appears that no body of substantive research on these subjects is accessibly available.

There is, however, one major exception to that conclusion and her name is Dr. Joy M. Ebben. Describing herself as a "Human Factors/Ergonomics Specialist," Dr. Ebben has for the past 11 years quietly been researching the very questions that are being raised here. Her credentials for the undertaking include an MS in Education, an MA in Human Factors and Applied Experimental Psychology, and a Ph.D. in Applied Cognitive Psychology.

There are a few people in our industry who know about her and about her work. But only a few. That ought to change. Dr. Ebben, who lives and works in Alta Loma, CA can be reached by voice at 909-941-4539 or electronically at PhDJoy@aol.com.

When analyzing a potential display system, Dr. Ebben believes that the first criterion centers on the question of size and may be summed up as asking (lots of times), "Is it big enough?"

When confronted by our industry’s current supposition that an adequate screen height can be determined by dividing the distance to the least favored viewer by the number 6, she was frankly skeptical. And, although this series has been enthusiastic in the promulgation of that standard, Dr. Ebben’s mistrust of its reliability may, on second thought, be justified.

While wholeheartedly agreeing that screens displaying data that must be read by their audiences need to be bigger than screens presenting images that need merely to be recognized, she doubts that establishing the size of the "page" can by itself authenticate the intelligibility of the data to be "written" on it.

Here is a brief initial summary of her Human Factor Goals:

· To help ensure that users can:

-See the information
-Detect changes in the information
-Discriminate bits of information
-Understand the information

· As required to perform their functions or tasks.

The reason, Dr. Ebben points out, that display systems are provided in the first place is "to provide information to people. If those people cannot see, read, discriminate, and understand what is being presented, the system has failed."

Eight of the system specification criteria which Dr. Ebben contends must be considered are:

1) Perceived Character Size
2) Alphanumeric and Graphic Designs
3) Vertical Viewing Fields
4) Horizontal Viewing Fields
5) Vertical Screen Dispersion
6) Horizontal Screen Dispersion
7) Unobstructed Viewing
8) Room Layout



Figure 1

From analyzing the interrelationships between these metrics, Dr. Ebben produces recommendations for five intelligibility parameters:

I. Screen size, location, height, and configuration
II. Screen and Projector tilt
III. Closest seating
IV. Prioritized seating areas
V. Character size relative to design criteria



Figure 2

Figures 1 and 2 illustrate how viewing angles to projected symbols get measured. Dr. Ebben is convincing when she asserts that the only reliable way to ensure that the symbols are big enough for an audience to read is to calculate the character size on the retina of each viewer’s eyes. To do this, she solves for what is called the "subtended angle" (Figure 3) which is best expressed in minutes of arc. (An arc minute is defined as a unit of angular measurement equal to one sixtieth of a degree, or 60 arc seconds.)



Figure 3

As may be seen from Figure 4, it turns out that the minimum height for the smallest symbol should subtend not less than 10 arc minutes. What the table also reveals, however, is that 10' is only reliable for viewers positioned nearly normal to the display.



Figure 4

Because all other viewers are obliged to look at the display, as it were, askance, their visual task is incrementally more demanding and the size of the symbols must for them be proportionately increased.

To see what else may be necessary to the creation of intelligible displays, however, will require examining them from yet additional angles of view.