Minimum Effective Dose of Accuracy
Day in and day out reality capture solutions seem to be appearing out of thin air with solutions pushing the level of accuracy into tighter tolerances while at the same time a newer breed of less accurate solutions are emerging at considerably less cost.
It is easy for professionals in the reality capture industry to become consumed by the chase for increased accuracy and range, but lately we have seen a rise of a new breed of reality capture devices. Reality capture is no longer a race for accuracy. The market has seen a greater need beyond accuracy; other conditions need to be taken into consideration such as cost and speed. With these considerations entering a potential customer’s field, the reality capture industry has evolved into a spectrum of accuracies coupled with the issues of time and cost.
You may be familiar with the Pareto Principle which states that basically for many events, roughly 80% of the effects come from 20% of the causes. This concept was noted by Vilfredo Pareto in an analysis of the land ownership in Italy where he found that 80% of the land in Italy was owned by 20% of the population. This concept has been adopted in many methodologies and strategies from business management to income and economics. It lends itself to the search for the main “causes” that lead to the majority of “events.” With the rapidly developing market for reality capture, we are seeing efforts being poured into other aspects of accuracy such as lower cost and improved workflows.
Pareto’s Principle, also known as the 80/20 rule, is being realized in today’s market for several reasons. To start, the need for sub millimeter accuracy levels have begun to plateau and it has grown increasingly difficult to improve sub-millimeter accuracy as well as prove claims to such a level consistently from project to project. Millimeter and lower accuracies are not easy to achieve and therefore demand a higher price point which limits the amount of usage and vice versa, the less accurate is easier to come by and therefore can provide a lower price point and potentially integrate with quicker techniques for capture.
Photogrammetry is just one example of how the reality capture market has expanded. With equipment costs of less than $2,000, professionals are regularly seeing results to within 90% of a professional grade 3D laser scanning system that costs around the range of $200,000. The results I am referencing refer to many UAV operations utilizing ground control points and an approximate flight height of 200 ft. above ground level. Many other 3D depth sensing cameras and photogrammetric solutions on the market now vary in price and claim results within this range of accuracy. Regardless of whether the claims are valid, the main point is that the amount of accuracy achieved is “good enough,” as other needs are being achieved in other aspects of the reality capture workflow.
Buyers and service providers are realizing that millimeter accuracy is not always necessary for every project. Potentially, a UAV flight that can demonstrate accuracies to within 6” would be more effective and allow for more opportunities for data capture. Lately, it seems accuracy specs have been secondary to speed and cost. Subcontractors can garner more value from an increased number of captures over infrequent but far too accurate captures.
Because of this new market opportunity, many new players are entering the market with combinations of mobile LiDAR units, integrated IMUs and additional sensors to make up for loss of accuracy in speed of capture. Proof of this growing need for new reality capture devices can be seen by well-established players in the high accuracy market making plays at lower cost, faster, reduced accuracy solutions. High accuracy is still a priority, but the product line is expanding into faster capture devices with reduced levels of accuracy and at cheaper price points.
The term minimum effective dose originated from the medical profession and is critical in determining the therapeutic range of a drug. The minimum effective dose (MED) is the lowest dose level of a pharmaceutical product that provides a clinically significant response in average efficacy. Therefore, when a project presents itself, we often ask what accuracy is required. Essentially, we are looking to determine the lowest increment of accuracy to provide a significant level for an effective representation of the project. So I end by asking the question, what is your minimum effective dose of accuracy?
Tony Sabat, BIM/CAD Technical Specialist