DJI Zenmuse H20T

The camera with the widest range of uses is definitely the DJI Zenmuse H20T. As such, it consists of 4 sensors – wide-angle, zoom and thermal, plus an additional sensor – a laser rangefinder.

DJI H20T Technical Specifications

The DJI Zenmuse H20T camera has found application especially in cooperation with the Fire Department. Its biggest advantage in these situations is the thermal imaging capability, which makes it possible to locate fire outbreaks. This information is crucial for the HZS (Fire and Rescue Service), as it gives them an overview of the extent and distribution of the fire and can therefore suppress its spread in time. During the intervention, we stream the image from the camera using our IZS Stream application directly to the device (phone / tablet / computer) of the intervention commander, who can thus use the information obtained to assess the state of the fire and distribute the forces as the current situation requires. If you are interested in learning more about this application, be sure to visit the IZS Stream project in the projects tab.

Another fairly common type of callout where the DJI Zenmuse H20T camera is the first choice is a search for people. The combination of thermal imaging and up to 200x hybrid zoom capability has proven to be a powerful tool for this type of intervention. When searching, we use thermal imaging first. If we see a hot spot on the camera, we use the zoom camera to see if it is indeed the person we are looking for. At night, we also illuminate the suspicious spot with a spotlight that we have attached next to the camera. During these interventions, we also use the 4th sensor on this camera, which is the range finder. It can give us a distance of up to 1200 meters and, thanks to the knowledge of the UAV position and the camera orientation, it can calculate the approximate GPS position of the target. So as soon as we spot a suspicious point during a search operation, we can relay that GPS location to the police or fire brigade units. The GPS location is visible on the screen of the controller and for ease of forwarding, we have developed an application that runs in the background of the controller. When a point is found, the app reads its location from the image, sends it to the server, where our IZS app then draws the stream. In this second application, we can then see both the image transmission from the UAV and the currently located point on the map background. The unit member can then be navigated through this application to the target point.

DJI Zenmuse L1

Another multi-sensor camera that we use in our engagements with the IZS is the DJI Zenmuse L1. This can create a 3D model in the form of a point cloud thanks to its laser scanner, or LiDAR. We can live stream the results of the scan, and the entire scanning process can be viewed on a tablet that is integrated into the controller. It also has a wide-angle camera as well as a camera that is used to colour the point cloud.

We mainly use this camera to create point clouds and 3D models of various objects. This is mainly for documentation of collapsed buildings or buildings after fires. The data is then processed and forwarded to the Police or HZS for further analysis.

Also, the DJI Zenmuse L1 has been used for traffic police needs to document the scene of a serious traffic accident, thanks to its high-quality wide-angle RGB camera. However, it has been replaced by the even higher quality DJI Zenmuse P1 camera. Currently, the L1 is thus maintained more as a backup camera for dual isochrone events.

DJI Zenmuse P1

This is a full-frame camera that, thanks to its high resolution, excels above the rest in tasks such as aerial photography or photogrammetry. It can be equipped with three different lenses (24/35/50mm). However, after a short test, we found the 35mm lens to be sufficient for several reasons:

• When used during a night mission at the same time as the spotlight to illuminate the area to be documented, this lens provides us with a view of only the illuminated area, so there is almost no post-processing required due to the illumination
• It is optimal for the mission setup, the best compromise between the parameters: flight time, flight speed, flight altitude, number of trajectories to document the whole area (especially at the site of traffic accidents, we have to act as fast as possible to avoid slowing down the local traffic on the road)

DJI Zenmus P1 Technical Specification

As already mentioned, the DJI Zenmuse P1 has replaced the DJI Zenmuse L1 and DJI Zenmuse H20T in capturing traffic accidents for the Police Department. It has also found use, for example, in documenting a building after a fire, where it can create a very accurate 3D model from the photos.

Comparison of cameras

As already mentioned, each camera is suitable for a different type of intervention. It is therefore impossible to say that one is better than the other. What can be compared, however, is the quality of the photographs taken from the RGB sensors of each camera. We conducted this test primarily to see how much the quality of the traffic accidents captured would differ when using each camera, both in daylight and at night.

Day flights

The photos were taken from the same height (30m) with the same lighting and the same drone speed. No additional lighting (such as a spotlight) was used for the night flight photos.

In the photographs, we can notice that the L1 camera, which was previously used to capture accidents during daylight hours, can capture the edges of the object better compared to the H20T, but this is at the expense of colour saturation. In contrast, the P1 camera preserves both the sharp edges of the object and the colours.

When documenting traffic accidents, it is important that once the orthophoto image is assembled, no details of the objects present at the accident site are lost. How the cameras were able to cope with the thin lamp can be seen in the following photographs.

Night flights

In the previous paragraphs, we mentioned that we used the L1 camera to capture accidents in daylight. However, for night flights, the H20T camera was used due to its better light sensitivity. However, it too was replaced by the P1 camera for these purposes. The following photos will make it clear why.

When capturing night crashes, it is necessary to capture as accurately as possible the vehicles involved as well as the wreckage, investigator markings, or braking paths. All of this needs to be captured with as much accuracy as possible.

In the last photographs we can again see what problems the cameras can have after composing the orthophoto image with the lamps.

Reflector

To further improve the night imaging we have developed a custom reflector. This replaces the GL60 ZOOM and Z15 spotlight used so far. The advantage of our developed reflector is the larger angle of illumination. When used with the DJI Zenmuse P1 camera in combination with a 35mm lens, it is then almost perfectly formed. It makes photos evenly lit, as opposed to the over-lit centers and dark edges of before.

Not only during night missions, but also during daytime missions, we are able to provide the necessary high level of quality with the DJI Zenmuse P1 camera. However, with higher quality comes an increase in the volume of data we process and pass on to investigators. This brings with it new constraints, which we manage to overcome with the applications we have developed.