Overview
Over the past few years, there has been an influx of high-megapixel drone cameras with large sensors introduced to the drone mapping and inspection market.
Third-party cameras and even some bolt-on cameras by the leading drone manufacturers can have a sensor-width exceeding 40mm and megapixel rating between 40MP and 100MP.
On the other hand, advances in camera technology have given drone manufacturers the opportunity to integrate high-end cameras to their products without compromising on size. For example, the DJI Mavic & Phantom Series.
But how do built-in cameras compare with high-end third party cameras when it comes to photogrammetry?
In this case study, we will be looking at why these cameras have come to market and the value they bring when it comes to collecting data for photogrammetry. We will also be comparing the data collected when using third-party cameras vs drones with a high megapixel camera built-in, in this instance, we will compare results from a 50 MP Third Party Camera (at a higher altitude) will be put up against the 20 MP DJI Mavic 2 Pro (at a lower altitude).
NB: MP = Megapixels.
NB: We are not simply comparing a larger camera with a smaller one. We are comparing a large camera capturing from further away with a small camera capturing from much closer.
NB: Also, the 50MP camera has a larger sensor size (44m) when compared to that of the 20MP camera (13mm), which will also have an impact on image quality.
Why Do Sensor Sizes & Megapixels Matter?
Using a third-party 50MP / 61MP / 100 MP camera or even a high-end bolt-on like DJI's P1 will have its advantages over the likes of a drone with a built-in camera, but what are those advantages, and are there any disadvantages?
Advantages
1. Data Quality: Using a high-megapixel drone camera gives you the ability to shoot with a low GSD (Ground Sampling Distance) i.e a higher resolution at a greater distance from the target site or asset. Shooting with a 50-megapixel camera at 190ft, for example, means that you will collect higher resolution imagery than that of a 20-megapixel camera:
50 Megapixel @ 190ft = GSD 0.31 cm/pixel 20 Megapixel @ 190ft = GSD 1.08 cm/pixel
For more information on GSD please see our article:
So, you can definitely get higher quality data at same height from a higher MP camera than a lower one. This means that you can be at a safe distance from the target whilst collecting high quality data. This is great advantage, particularly in situations where access to lower altitudes on the job site is restricted.
2. Flight Time: Flying at a higher altitude and collecting high-quality drone data due to the high megapixel count, will typically also (but not always!) decrease the flight time that the drone needs to be in the air.
Below you can two examples of flights conducted using Hammer Missions using the a 50 MP camera on the DJI M300 compared with the DJI Mavic 2 Pro camera. The aircraft were flown at 190ft and 90ft respectively to achieve the same data quality.
Disadvantages
1. Increased Setup Time: To be able to carry the larger third-party cameras the operator will need a larger drone to be able to handle the weight of the externally fitted camera. With the externally fitted camera and the larger rig, you must take into account that the setup times will be considerably longer before you are able to get airborne.
Working with larger drones and third-party cameras might also incur further setup costs as the integration between the drone and third-party cameras might still be work in progress.
2. Bigger Datasets: The Higher Megapixel count naturally means bigger datasets generated during the flight. This would typically mean higher costs in data storage and longer waiting times in moving the data around, which might be limited by your internet connection speeds!
But wait, what about the camera prices?
High Megapixel drone cameras typically cost more than in-built ones. But we think that these costs can be justified based on your use-case. If extremely high data quality and efficient flight speeds are your number #1 priority and you are able to work around the challenges of higher setup costs and bigger datasets, then a higher megapixel camera makes a lot of sense! This would typically be the case if you are flying multiple missions in remote areas regularly.
Can you get the same quality data from a built-in camera?
Drones with built-in cameras have come a long way and have become very popular with both consumers and professionals but can they produce the quality you would need for drone photogrammetry or 3D Mapping?
The simple answer is 'It depends'. You would have to fly at a lower altitude to be able to match the GSD (ground sampling distance) of a drone with a high megapixel camera. This in turn would also lower the image footprint that your camera produces.
20 Megapixel @ 80ft = GSD 0.31 cm/pixel 50 Megapixel @ 190ft = GSD 0.31 cm/pixel
You obviously still have to take into account that the resolution of the final image from the 50-megapixel camera will be higher than that of the 20-megapixel camera when the 3D model has been created.
Again, let's talk about the advantages and disadvantages of drones with built-in cameras.
Advantages
1. Quicker Setup: Drones with built-in cameras are often ready to fly within minutes of unpacking, therefore this can greatly reduce your time on the ground and can get you in the air quicker.
2. Lowered Costs: Drones have come down in price over the years and you can now pick up a drone that is capable of good data collection for photogrammetry for a very reasonable price. Moreover, the data generated by the flight would be easier to transfer, store and work with in terms of pure dataset sizes.
Disadvantages
1. Data Quality: To be able to get the quality required for photogrammetry means increased flight time as you would have to fly lower to be able to collect the same amount of data. This puts your drone at a higher risk and would take longer to complete your mission to obtain your 3D model.
Not to mention, that if both cameras have safe access to the same flying altitudes, then the 50 MP camera would win by default!
2. Flight Times: Depending on the area size, you might experience higher flight times as you would have to fly that much closer to the subject to get the same quality as the high-MP camera.
The Results - 50 Megapixel Camera vs DJI Mavic 2 Pro
To validate this theory we field tested a third party 50 MP camera and DJI Mavic 2 Pro in a head-to-head comparison.
Both drones were taken to the same site for testing and flown under nearly similar conditions on all occasions.
50 MP Camera (at 190ft)
A third party 50 MP camera was flown first, the flight was conducted at 190ft with a ground offset of 35ft (the height of the structure we were capturing).
Two missions were flown, 3D Mapping followed by a tower mission (single pass) to capture the obliques. The gimbal was set at -90 degrees for the 3D mapping mission and -61 degrees for the orbit mission.
Data Captured and Processed using Hammer Missions
DJI Mavic 2 Pro (at 190ft)
To match the above test the DJI Mavic 2 Pro was also flown at 190ft with a ground offset of 35ft.
Again, two missions were flown, 3D Mapping and a Orbit Missions for obliques, gimbal setting were matched to those of the original baseline test.
Data Captured and Processed using Hammer Missions
DJI Mavic 2 Pro (90ft)
The third and final test was performed with the DJI Mavic 2 Pro flown at an altitude of 90 feet so that we could near match the GSD of the baseline test.
The baseline test GSD was 0.31 cm/pixel, flying the DJI Mavic 2 Pro at 90ft gave us a GSD of 0.38 cm/pixel. To match the GSD of the baseline we would have to have flown at 80ft but chose 90ft to mitigate risk on site.
Two missions were flown, 3D Mapping followed by a tower mission (single pass) to capture the obliques. The gimbal was set at -90 degrees for the 3D mapping mission and -41degrees for the orbit mission.
Data Captured and Processed using Hammer Missions
Analysis
We compared the 50 MP camera to the 20 MP camera on 4 main metrics:
Data Quality
Flight Time
Setup Time
Dataset Sizes
1. Data Quality
To compare performance on data quality, we chose 3 random locations in the 3D model and observed the feature detail in the 3D mesh.
By isolating parts of the 3D models, it's quite clear the best quality 3D model was produced by the 50 MP camera at 190 ft, followed by the 20 MP at 90ft and 20 MP camera at 190ft.
It should be noted here that the higher quality of the mesh may be attributed to not just the higher megapixels of the 50MP camera but also the higher sensor size (44mm) as compared to that of the 20 MP camera (13mm).
You can access the 3D datasets for yourself using the links below:
2. Flight Times
50 MP @ 190ft = ~3 min 20 MP @ 90ft = ~3.6 min 20 MP @ 190ft = ~1.5 min
Note - These flight times might differ for larger areas. Overall, we found that the lowest flight times can be achieved by using the 20 MP @ 190ft, however, for the same data quality, a 50 MP camera would be better than the 20 MP camera.
3. Setup Time
50 MP @ 190ft = 10-15 min 20 MP @ 90ft = 0 min 20 MP @ 190ft = 0 min
No surprises here. A built in camera would involve next to nothing when it comes to hardware setup time. Depending on whether the high MP camera is sold by the drone manufacturer or by a third party, the setup time can vary from 5-15 min.
4. Dataset Sizes
50 MP @ 190ft = 145 pictures, 62 MB each = ~9GB 20 MP @ 90ft = 178 pictures, 6.4 MB each = ~1.2 GB 20 MP @ 190ft = 69 pictures, 6.4 MB each = ~450 MB
The 50 MP camera produces nearly 10 times as much data than the 20 MP camera, when flown for the same GSD, and nearly 20 times as much data when flown at the same altitude!
Conclusion
Overall, here's how we found the different cameras to rank on across different metrics:
| 50 MP Camera (190 ft) | 20 MP Camera (90 ft) | 20 MP Camera (190 ft) |
Data Quality | Highest | High | Low |
Flight Time | Lowest | High | Low |
Setup Time | Highest | Lowest | Lowest |
Dataset Sizes | Highest | High | Lowest |
But, what about the 50 MP Camera at 90ft? Unfortunately, we didn't deem it safe to fly the 50 MP Camera at 90ft due to the greater drone size. This is also an important consideration to keep in mind. An integrated lower megapixel camera would be easier to fly in residential areas than a high MP third-party camera on the DJI M300 drone.
So in conclusion, high-megapixel cameras rightfully do have their place in the market and can produce much higher quality results in lowered flight time but do you have the jobs, use-cases and hardware infrastructure to be able to produce these consistently, or do the smaller drones with built-in cameras suit your use case? That is the key question to think about.
One strategy is to invest in both cameras, and to use the right camera for the right job.
In the video below Alex and Varun from Hammer Missions talk extensively about Drone Cameras and explain the advantages and disadvantages in the drone industry.
Summary
We hope this guide helps you understand the different factors to consider when thinking about megapixels and how they affect drone photogrammetry.
If you'd like to learn more about how to capture high-quality data and get the most out of your drone flights using our cloud-based platform, please feel free to visit our learning resources.
If you haven't got a Hammer account and would like to try Hammer Missions you can get started on our free trial.
To learn more about our enterprise solutions, including mission collaboration, data processing, and AI solutions, please contact us at team@hammermissions.com.
We look forward to hearing from you.
— Team at Hammer Missions