April 1, 2015
By Brian Jewell, P.Eng
Pool measuring has been a large part of a service professional’s job for many years. The skill to measure accurately takes training, patience, and time as they are necessary for the successful installation of high-priced custom fabricated vinyl liners and safety covers. Correct measurements not only ensure products fit properly, but also help projects operate more efficiently. The end result leads to reduced installation labour, satisfied customers, quicker payment, and a reputation for quality work.
The consequences of poor measurements can be disastrous for an installer. Shoddy work can mean having to re-measure a pool for replacement orders, dissatisfied customers, difficulty in collecting payment, and increased labour costs. Even if the installation can be completed, the lifespan of a poor-fitting vinyl liner may be compromised due to wrinkles, premature fading, and tension, which further leads to tears or separation from the pool coping.
These problems can be costly, which has motivated the industry to look for ways to improve the ease and accuracy of pool measuring. The innovative results have allowed for more successful installations and increased revenue for installers. The developed measuring methods have also allowed for more complex designs. Rather than simple rectangle and round vessels, pool shapes have become extremely complex, including vinyl-covered swim outs, vinyl-over stairs, as well as safety covers covering complex water features, etc. All of these complicated features and designs are supported by better measuring techniques and technology.
Newer methods have also aimed to save the installer time, which is extremely important during the short pool season. Good ‘A-B’ measurements can take a two-person team roughly an hour to complete; however, using today’s newer technology, the time saved can be used to generate additional income instead.
Technology using digital photographs to create 3D pool models is one of the most recent developments available to industry professionals. This technique involves taking approximately 20 eight-megapixel photos of the pool from various locations. After they are submitted to the manufacturer, they are processed to generate an accurate 3D pool model. These models are then used to manufacture custom items such as vinyl liners and safety covers. The accuracy and simplicity of the technology provides incredibly precise results with minimal effort. Further, the only hardware required is an eight-megapixel camera.
The picture measuring technology captures complex items such as freeform lines or concave and convex surfaces. Pools of complex geometry can be measured by a single worker in a few minutes with very little training or instruction.
However, before photos can be taken as part of this measuring technique, the pool must be near empty and relatively dry. Further, taking ‘good’ pictures are important to getting accurate results; therefore, photos must be clear and in focus without any moving objects in the pool. Water-filled areas of the pool will not generate a 3D model.
Some point-and-shoot cameras as well as most mobile phones have the capability to take photos at the quality required for the 3D modelling software.
Thousands of items within each high-resolution photo are recognized. By recognizing the points in the photos, and the relative distance between them, their 3D location can be determined using algebra. The photos are processed using software to identify all of the recognized locations. All of the processing and expertise is completed by the fabricator’s design staff and is not a concern for the installer. The installer simply provides the photos along with a few measurements, depending on the manufacturers request. These measurements are used to properly scale the 3D model.
|• Model entire pool, including floor shape.||• Pool must be empty.|
|• Accurate.||• No results until submitted and processed by the manufacturer.|
|• Inexpensive equipment.|
Laser measuring systems
Laser measuring systems entered the market in a more significant way approximately three years ago. Lasers offer incredible accuracy—within 1.6 mm (0.062 in.)—and can be used to calculate lengths, widths, and heights up to approximately 198 m (650 ft). They can also be used to measure complex pool shapes. Laser 3D imaging systems can measure an entire pool extremely fast; including time for set-up, depending on how many source locations are required, a pool can be completely measured between 25 minutes to three hours (approximate).
Different source locations are needed when using this measuring system as the laser is a ‘line of sight’ device; if there are surfaces that cannot be seen from the laser location, it must be moved as many times as required to capture all of the pool surfaces.
The distance calculation is completed through precision optics and laser physics, using the phase-shift method, in which the laser hits an object and compares its reflection with the beam sent out, or using the time-of-flight method, whereby calculating the time it takes for an optical pulse to reflect back. Together with the laser orientation at the time the measurement is taken, the 3D point is defined. Taking thousands of measurements generates the 3D pool model.
The results can be seen and reviewed by the operator at the job site before being submitted to the manufacturer. The file output is in a convenient .DXF format, which is a common computer-aided drawing (CAD) format readily read and processed by manufacturers.
The equipment for a 3D laser measuring system is approximately $14,000 (U.S.) and there are a few options available from different manufacturers.
|• Model entire pool, including floor shape.||• Expensive hardware.|
|• Extremely accurate.||• Pool must be empty.|
|• Able to review results in field.|
Triangulation (also known as A-B measuring) has been the industry standard for decades. It is an inexpensive method that requires little training. Using two stakes as a co-ordinate base, along with the distance between them, any point in the same 2D plane can be pinpointed by taking the distance from each of the stakes using multiple measuring tapes (one from each stake). Then, measurements from each stake to several points around the pool perimeter are taken, approximately one every 0.6 m (2 ft). This measuring method can take roughly an hour to complete on a relatively simple pool with two people on-site (one person to take the measurements and the other to record them).
Although the results from A-B measuring can be quite accurate, they are prone to errors as stake placement can lead to sensitivity of resulting plots, communicating and recording errors, measuring tapes getting caught on objects, points taken are too course to get good resolution, etc.
If the installer uses computer-based verification software, they should be able to identify most errors before leaving the field. A-B points are also limited to the pool perimeter and do not include definition of the pool floor.
|• Simple.||• Two dimensional.|
|• Inexpensive tools.||• Prone to errors.|
|• Results can be reviewed in the field (when used with software).||• Time consuming.|
|• Pool can be filled with water.||• Poor resolution/lack of detail.|
History of pool measuring
Of course, it was not always easy to measure pools. It was a long road to get the industry to where it is today. When vinyl liner pools were first being installed, installers were usually expected to build the pool to a specific size based on a short list of standard dimensions (generally rectangles with 152.4-mm [6-in.] radius corners). Typically, the pool was not measured for the manufacturer of the liner or cover. Instead, the pool was designed around a standard liner size.
Building the pool to exact specifications was not always possible or desirable, so some manufacturers went as far as building the liner in the pool, eliminating the need to accurately measure and recreate the measurements during the fabrication process.
Measuring rectangular pools, which were popular at this time, were pretty straight forward. Standard measuring sheets were developed to help the installer ensure they recorded all of the necessary measurements. Octagonal-, full-‘L’s and kidney-shaped pools all lent themselves to these measuring sheets as well. They generally included measurements of the pool’s wall lengths, diagonals, and depths—essentially the basic measurements to recreate the pool shape.
As consumers started to request more elaborate pool shapes, it became necessary for designers/ builders to communicate specific measurements to the vinyl liner or safety cover fabricator. This increased product efficiency as they were more often than not manufactured in a facility using state-of-the-art equipment rather than improvising the installation on the jobsite. This also eliminated many environmental influences of working outdoors.
Before digital technology, and prior to the ‘A-B’ triangulation measurement method, installers and manufacturers used a system where a rope was run down the middle of the pool with markings every 0.61 m (2 ft). Dimensions from, and perpendicular to, the rope to each side of the pool’s edge were recorded. This created a grid pattern that defined the pool’s perimeter. Over time, however, ‘A-B’ measuring became the preferred method for defining a pool’s perimeter.
Today, the task of pool measuring is shifting toward newer techniques not only as a result of recent advancements in computer hardware and software, but also because the current generation of industry professionals is more willing to embrace new technology.
The process of measuring pools has changed considerably and as more installers make use of these tools many will see their benefits. As technology continues to advance, it will be interesting to see how pool measuring will continue to evolve.
Brian Jewell, P.Eng., is an owner of Highbury Pools Ltd., a manufacturer of various swimming pool components in Arva, Ont. He oversees the company’s liner manufacturing facility and has more than 20 years’ experience in the pool industry. Jewell received his degree in mechanical engineering in 1998 and is a registered professional engineer in Ontario, Alberta, and Michigan. He can be reached via e-mail at firstname.lastname@example.org.
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