How can a camera replace the conventional A-B method of measuring a pool?

Photogrammetry. That’s how.

The science of deducing physical dimensions from photographs dates back to the Renaissance era when Leonardo da Vinci and his contemporaries experimented with the principals of perception and geometry, leading the way for the film projector and other technologies.

Today, photogrammetry is used in a variety of fields, including aerospace, archeology, forensics and accident reconstruction. In the latter, police officers can quickly process crash scenes by snapping a few photos. They’re in and out in a matter of minutes, much to the relief of motorists stalled in traffic.

If it works for archeologists and investigators, why not pool service technicians?

By all accounts, it works brilliantly, cover dealers say.

Chuck Calhoun was understandably skeptical when it was brought to his attention that a digital camera could effectively “map” the geometry of a pool.

“I found it hard to believe they could measure a picture,” says the owner of Pools & Spas Service in Monmouth County, N.J. “But they did it!” By ‘they,’ he means Loop-Loc. The Hauppauge, N.Y.-based cover manufacturer introduced its proprietary Image-Loc technology three years ago.

Calhoun doubted that one person with a digital camera could get accurate dimensions in less than half the time it would take a team of two. But, faced with measuring a complicated, multilevel pool with a waterfall, he gave the program a shot. The resulting cover came back from the factory fitting the contours like a glove.

“I was hesitant to order such a large, expensive cover based on some photos,” he says, “but to my surprise there were no mistakes when the cover came in.”

“That kind of job would be 300 measurements the old way,” Calhoun adds.

The old way. Using the A-B approach, a pool’s perimeter is plotted using reference pegs, fiberglass role tape and chalk. Measurements are recorded on a sheet of paper. Dimensions are then sent to the fabricator. It’s typically a two-person, time consuming job.

“I’ve been in the industry for 15 years and everyone has always been asking for a better way to measure,” says Mike Preuit, national sales and product manager with CoverLogix. The Portland, Ore.-based manufacturer recently armed its dealers with PhotoLogix, another photogrammetry software system. Several other manufacturers have similar methods, and while each product varies, the basic principal applies, that being image-based triangulation.

Consider that a photograph essentially converts our three dimensional world to a 2-D image. Photogrammetry is the reverse of that. It reconstructs flat images to a 3-D model. That’s a gross oversimplification, but you get the picture.

One snapshot of a pool, however, isn’t going to cut it. Photogrammetry relies on the use of multiple photos, each offering a different overlapping perspective view of the object being measured.

For pool cover purposes, it’s generally recommended that you start with high oblique camera views to establish the area you intend to measure. No need to climb the roof; a tall ladder will do. Move the ladder around the pool to get plenty of overlapping images. A software program essentially stitches these images together to scale a 3-D environment.

“Photogrammetry is all about redundancy,” explains Lee DeChant, the co-developer of iWitnessPRO, a photogrammetry software program widely used in forensics. Several cover manufacturers have adopted iWitness to streamline the measurement process. “If you have less than three images,” he adds, “then there is no redundancy and accuracy can become questionable.”

Having discrete features to reference in multiple photos is equally important. The photographer will first have to lay targets around the pool. Depending on the program, these can be short pieces of lumber, or reflective targets that are identified automatically in the photo processing stage.

Yet tape measures still have a role to play. Professionals need to measure the distance between two reference points and input that information into the computer program in order to determine scale. Once the photos are imported, the PC-based photogrammetry software determines the camera’s aim and calculates the 3-D measurement points. Then it’s ready for CAD layout work.

“The software program scales everything out and makes the cover fit like a dream,” says Mike Dominici, a Loop-Loc dealer and owner of Long Island Pool & Patio in Coram, N.Y. The fact that the job can be done solo sold him on it. “That’s one less person I have to send out, and secondly, there’s no call-backs. You don’t have to go back and check measurements, ever.”

Call backs: The bane of every dealer’s existence. Two cover installers could spend hours measuring a pool only to find out from the fabricator that, hey, something isn’t right here, which means dealers will have to go back to the site and recheck their work.

Before photogrammetry was an option, manufacturers developed software programs designed to minimize mistakes in the field. Laptop-equipped dealers would input their measurements into a plotting program to receive immediate confirmation that their dimensions were accurate. These programs are still widely used today, but they do not reduce manpower or save time on the job the way photogrammetry-based technology can.

“The accuracy we’ve found with it is far superior to the old method, and from the dealer’s standpoint it’s extremely fast,” says Preuit, adding that it’s accurate to within a fraction of an inch.

Not only can photogrammetry accurately plot a pool’s shape, Preuit adds, the process also identifies elevated features, such as waterfalls, and other intrusions that would have to be hand-measured otherwise.

It works just as well for cover replacements, too. Photogrammetry can identify existing anchor points on a pool deck, so dealers won’t have to box and ship the old cover to the fabricator for replication.

Cover dealers do much of their business in the fall, finding prospective customers through service technicians closing backyard pools for the winter. Given their sales are largely seasonal, speed is essential.

“It’s a much quicker turnaround,” says John Zanfardino, Loop-Loc’s design manager.

While efficiency is certainly a selling point, Ritchie Cameron is more concerned with getting the job right.

“I don’t have to be concerned that I wrote down the wrong number, or someone else yelled the wrong number,” says Cameron, a design consultant with Classic Pool Spa & Hearth, a CoverLogix dealer serving Oregon’s Portland area. “I’ve had both happen.”

Once he take the pictures — he admits he takes far more than probably necessary, but he likes to be thorough — it’s only a matter of uploading the photos into a file sharing program so CoverLogix can process them.

So, photogrammetry has covers covered. What about vinyl liners?

“Can it be done? Absolutely,” DeChant says.

The same principal applies; however, because a basin’s contours are less defined as, say, pool coping, it would require a series of discrete markers throughout.

But its potential doesn’t end there.

“My clients are more excited about where we’re going with this,” DeChant says.

And where would that be?

Look up.

Imagine an unmanned aerial vehicle snapping shots of a pool as it soars overhead, completing the work in a fraction of the time.

Candid about cameras

Can an inexpensive digital camera do the job, or will the cover installer have to invest in more sophisticated photo equipment?

Lee DeChant, a photogrammetry consultant, cautions against cheap point-and-shoots. For more accurate results, consider something more advanced.

Photogrammetry works because it can determine the camera’s principal distance, or focal length, from the object being photographed. The problem with simple cameras is that they operate in autofocus, conflicting with the fundamentals of metric measurement. Because they typically don’t offer manual settings, there usually isn’t a way to remedy this.

Ideally, a digital single-lens reflex camera should be used with photogrammetry software systems because the lens can be locked “to focus on infinity.” That means the camera can focus on something infinitely far away, providing for optimal accuracy.

Does that mean dealers have to shell out $2,000 for a high-end camera? No. DeChant recommends using a “bridge” camera, essentially something between cheap and expensive, such as the Canon PowerShot and Nikon Coolpix. Properly calibrated, these cameras fulfill the necessary requirements for reliable image-based measurement.

Beaming with efficiency

It seems the industry is determined to make A-B measuring a thing of the past. Not only do we have photo-imaging available, we now have laser technology for quick pool plotting.

Both Merlin Industries and Tara Manufacturing are rolling out laser-based measuring systems.

The beam-emitting, tripod-mounted devices determine length, width and depth, lending themselves to both vinyl and cover measurements. Simply set them in the shallow end of an empty basin and a rotating head scans the pool. The technology outputs the dimensions with laser precision.

“Anybody can use it. You don’t have to be an experienced pool professional. You just set it up and let it go,” says Thomas Kennedy, marketing director with Alabama-based Tara Manufacturing, maker of custom inground vinyl liners and the new Tara Laser device.

Similarly, Hamilton, N.J.’s Merlin Industries, says its system, Pin Point, will take the frustration out of manual measuring. T.J. Moreland, director of marketing and business development, says the 3-D imaging technology will be ideal for vinyl replacements and concrete conversions.