If Hasselblad are the tried and tested option, PhaseOne has become the maverick of the industrial camera industry.
Drone surveys are quickly becoming the fastest, most reliable way of carrying out inspections and surveys across the world. From powerline mapping to emergency response, sending a drone up into the air doesn’t just save time, it also saves money. But the drone is merely the delivery platform. Without the sensor, drone flight is rather a meaningless exercise, certainly in commercial terms. Without ranging and imagery, drones would never have taken off (excuse the pun) and would have remained the 21th Century equivalent of a flying a kite. Something best left to the hobbyists.
Before the age of the drone, airborne surveys were expensive and time-consuming. Nowadays, anyone with a drone and a camera can carry out a basic survey almost anywhere with differing results depending on the equipment used. While UAV sensors vary, (think LiDAR, gas detectors, thermal imaging), in the world of photogrammetry your survey results are only as good as your camera. But what do we mean by a good camera? We mean a metric camera.
Let’s start by defining the technology which we’re about to discuss. According to one definition, a “metric camera is one in which focal length and internal dimensions are exactly known or can be determined through calibration”. They are the most stable and affordable way to guarantee precise results from airborne surveys.
Before someone pipes up “what about LiDAR?” – remember we used the word affordable! Without debating, yet again, the merits of LiDAR Vs Photogrammetry, Photogrammetry remains the most cost-effective way of gathering accurate survey data in a short period of time – fact!
Metric cameras were designed specifically for photogrammetric surveys and in short, if you want to make precise measurements from photos, you’ll need one. There have been great advancements in the world of metric cameras and if you’re just starting out, or thinking of upgrading your kit, this blog seeks to help you get the best results, depending on your project, accuracy requirements and budget.
What’s so Special About a Metric Camera?
The main benefit of the metric camera is that the interior orientation parameters (or calibration) are more reliable. Simply put, they are more robust and stable. Changes in pressure, temperature or vibrations from the UAV or other platform don’t affect the internal mechanisms of a metric camera in the same way that they would a standard camera. Standard, even commercial, cameras simply haven’t been engineered to withstand the challenges which arise in airborne surveys. For example, even if the lens moves slightly, your images will suffer. Hasn’t your smartphone ever told you to steady your device? Well, with a metric camera, it’s steady even when you get into the air.
The quality of the lens also has a huge part to play. Metric camera lenses will give you a clear and crisp image all the way to the edge, without any distortion. Critical when you’re relying on ‘stitching’ hundreds of photos together to create a photomosaic for an accurate survey. There are lesser software companies (who shall remain nameless) who suggest the use of a higher overlap to combat the effects of distortion if using a standard commercial camera. This means even more images must be taken, costing your survey time and likely money. Or you could just use the right tools for the job in the first place?
Calibration is also a factor. A metric camera offers high repeatability for your survey results with less hassle. Unlike a standard commercial camera you don’t have to re-calibrate every time you fly. As much as software will do this on your behalf, it takes extra time and effort to make sure that you achieve the same results each time.
The Major Players in the Metric Camera Market
As with all technology, specialist imaging equipment has always had its major players. We’re talking about Zeiss, Nikon, Leica – all household names and all of whom continue to push the boundaries of imaging sensors after over a century in the business. In 2020 there may seem to be some new kids on the block when it comes to metric cameras but you may be surprised by their pedigree!
Hasselblad has produced some of the most iconic cameras in history but instead of chasing the global consumer camera revenue, Hasselblad specialised right from the offset. Despite being connected to the photography industry via Eastman-Kodak for decades, Hasselblad only produced their first camera, the HK-7 in 1941. This camera was specifically designed for airborne use and Hasselblad continue to break through boundaries by producing precisely engineered photographic sensors. Hasselblad cameras were also used for the majority of the still photographs taken when humankind first landed on the moon in 1969. Quite a pedigree indeed!
If Hasselblad are the tried and tested option, PhaseOne has become the maverick of the industrial camera industry. They may only have been around since the early 1990s, but what they lack in history they make up for in innovation. A product of the digital age, PhaseOne has not just revolutionised the aerial imaging industry, they’ve also combined their expertise in digital imaging with ground-breaking software to improve workflows and image processing. They are the Google to Hasselblad’s Microsoft if you will.
Let’s compare the options:
Metric Camera Comparison
We’ll be comparing the Hasselblad A6D with the PhaseOne iXM range, both of which have been designed to excel in the field of airborne surveys, specifically when mounted to a UAV.
1 – Weight:
The iXM is a whopping 1kg lighter than the A6D. This translates to an increased flight time with the PhaseOne metric camera. Both cameras have been design to work with the market leading commercial UAV – the DJI Matrice 600 but even with its huge 5.5kg payload capacity, depending on which lense you choose, you’ll be pushing your weight to the limit.
Both the PhaseOne iXM 100 and the iXM 50 both weigh in at 630g. Add the heaviest lense and your metric camera will still be sub 2kg. This will have a huge impact on flight duration and therefore the ease and cost of your aerial survey.
This round goes to Phase One.
2 – Frame Rate:
Your memory card inadvertently controls the frame rate of your camera as it’s down to their ability to store, or write, the information as it’s collected. Hasselblad’s A6D still uses older Compact Flash Cards (CF Cards) cards, whereas the PhaseOne iXM range utilises the more recently developed XQD cards.
Although Hasselblad claim that the A6D will trigger 1 frame every 0.85 seconds but thanks to XQD cards, the iXM100 can capture and log 3 frames per second, or 2 frames per second with the iXM50.
Again, this round goes to Phase One.
3 – CMOS Sensor:
Your CMOS sensor will determine the quality of your imagery in low light and let’s face it, unless you’re surveying in the Tropics, chances are you’ll suffer from lack of light at some stage in your survey. Photogrammetric surveys rely on good light. In winter or bad weather, many a survey has been halted when the light is lost.
In short, your CMOS sensor controls how much light is needed to get a properly exposed photo. The more light allowed to reach the sensor reduces image noise and improves image quality in low light conditions.
Hasselblad’s A6D uses a standard, and rather old, Sony CMOS sensor, whereas the PhaseOne iXM features a newer and highly improved CMOS BSI sensor. On a standard CMOS sensor, light has to pass through all kinds of wiring and circuitry before it can reach the photo diodes. With a BSI CMOS, the wiring is moved behind the light-receiving surface – allowing more light in. This also improves the capture speed, thanks to an improved analogue/digital conversion.
Again, Phase One comes out on top.
Infinity and Beyond
As we mentioned previously, the beauty of a metric camera is found in its stability. Another downside to the Hasselblad A6D is the use of an external focusing ring on the lense. When carrying out a mapping project, this ring has to be held in place by a grub screw. As you can imagine, the vibrations created by UAV flight can cause this screw to become loose or even fall out altogether. What’s worse, you don’t find out until you process your images – mission ruined!
Yet again, the PhaseOne team prove they have considered the challenges of airborne surveys and have locked their lenses to infinity as a factory standard. Their inspection lenses feature internal controllable focusing which is repeatable to within 6uM (published) or more often than not, 2uM.
Data Samples from the Phase One iXM
The main reason the PhaseOne iXM series slays the Hasselblad A6D is that it has been designed and developed specifically for aerial applications. It doesn’t use old parts to fit another purpose, each part has been specifically engineered for the job at hand. It’s not just the CF Cards which have been repurposed, the lenses can be interchanged between standard commercial applications and airborne applications. This may sound like a good thing but if you’re looking for clear imagery, accuracy and repeatability from your metric camera, the A6D is simply not up to the job.
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