Given the many voices on such a planning project, there are frequent disagreements about characteristics and features. Buying patterns may be determined by looking at customer receptivity for analogous features on the manufacturer’s or even competitors’ current instruments. Individual surveyors or groups of surveyors may be consulted. Results of questionnaires on what surveyors prefer or would like to see on future instruments may be reviewed.
Quite frequently, a new product process creates a line or series of instruments. And the relationship between the list price and the feature set of each model in the line may be furiously batted back and forth. Chief in the model differentiators is the angular and distance accuracy, if the product is a total station.
Now step with me into a different environment—the seminar or workshop. I present a number of papers and seminars, and teach classroom and hands-on courses every year. Many of them at least touch on the analysis of surveying work to be done and the design of the processes to accomplish it. Part of the design takes into account the capabilities of the instrument selected for the job (which may be the only instrument available to the surveyor). To illustrate these points, I will often ask the surveyors in attendance to tell me what instrument or instruments they typically use when a total station is required and what its distance and angle measuring accuracy is.
It never ceases to surprise me how few surveyors can tell me the salient details of their total stations. I’m not talking about whether they know the EDM’s maximum range, how much the magnification of the telescope is, or which technology is used in the angle sensor. I’m talking about model number, and angle and distance accuracy. I’ll be the first to admit that model number has slight importance in determining the quality or thoroughness of a surveyor’s work. But I ask this question because it is what I need to verify (or tell the surveyors) the accuracy of their instruments. Typically, in a group of 30 surveyors, the number who can answer at least one of the questions on accuracy (i.e. angle or distance) varies from zero to three.
Of course, surveying involves far more than accuracy considerations only. But when the single commonality between all types of surveyors is that they’re experts at making measurements on the Earth, isn’t making those measurements with appropriate accuracy a key part of that expertise?
I also understand that for many, understanding and considering the accuracy of their instruments is approached through intuitive or “gut-level” means. So, I am not saying that I have concluded scientifically (or unscientifically), that accuracy is not one of the variables in the surveyor’s equation for work. But I wonder about how our world, our profession and our professional lives would be different, if in my typical group of 30 surveyors, only three could not answer the instrument accuracy question.
Consumers of many different types, among whom I’m sure are many surveyors, take pride in knowing details about a craft or skill or technology or hobby or athletic pursuit. Many car enthusiasts understand, for example, how valve timing on an internal combustion engine can be changed to make it “hot.” They also usually understand the downsides of doing so. Runners spend a great deal of time understanding how training affects their bodies’ ability to use oxygen, how shin splints occur and how the principles of kinesiology are used in treating damaged muscles. Skiers can explicate on ski, pole, wax and snow types, and how to optimally use them to get the desired result. Anglers, hunters, scuba divers, golfers and even beer drinkers can expound at length on the intricate, and for the uninitiated, seemingly arcane details, of the complex system of interactions on which they have spent considerable energy to learn, understand and integrate into their pursuits.
Is it reasonable, then when comparing the level of knowledge and sophistication applied to a hobby, skill or interest, to expect any less from a surveyor to his profession?
If you take the position that surveying is a profession, and if you take the position that a profession requires, among other things, specialized knowledge to be held by the professional, shouldn’t the surveyor at a minimum know how the manufacturer rated the instrument’s angular and distance accuracy? And I mean really know, rather than stating that the least count of the instrument is the accuracy?
If you do take this position but have no idea what your instrument’s accuracy is, I suggest you pull out your instrument manual and check it out or contact your dealer or manufacturer. But it can’t stop here, because you will invariably be faced with terms that may not be obvious to you. A common designator for angular accuracy, for example, is DIN 18723, a German standard. Do you know that if your instrument is rated at ±2" by the DIN 18723 method, that it does not mean (necessarily) angle accuracy of 2"? It actually means that the mean of the direct and reverse readings to a single point will have a standard deviation of ±2". Using the formulas for propagation of random error, this means that the mean of an angle measured in the direct and reverse positions will have an standard deviation of ±2.8" (2" times the square root of 2). See a good book on errors analysis, such as “Surveying Measurements and Their Analysis” by Dr. R. B. Buckner for a detailed explanation of error propagation.
Design of surveys requires at a minimum, knowledge of the accuracy of your instrumentation. Make it your business to know this, and use it in your work.