Chengdu Rainpoo Technology Co., Ltd.

Chengdu Rainpoo Technology Co., Ltd.

Chengdu Rainpoo Technology Co., Ltd.

Corporate News

Article

Article
R&D line of Rainpoo’s product series

Through the introduction of How focal length affect 3D modeling results, you can have a preliminary understanding of the connection between the focal length and the FOV. From the setting of the flight parameters to 3D modeling process, these two parameters always have their place. So what effect do these two parameters have on the 3D modeling results? In this article, we’ll introduce how Rainpoo discovered the connection in the process of product R&D, and how to find a balance between the contradiction between flight height and 3D model result.

1、From D2 to D3

RIY-D2 is a product specially developed for cadastral survey projects. It is also the earliest oblique camera that adopts a drop-down and internal-lens design. D2 has high modeling accuracy and good modeling quality, which is suitable for scene modeling with flat terrain and not too high floors. However, for large drop, complex terrain and topography (including high-voltage lines, chimneys, base stations and other high-rise buildings), the flight safety of the drone will be a big problem.

 

In actual operations, some customers did not plan a good flight height, which caused the drone to hang high-voltage lines or hit the base station; Or even though some drones were lucky enough to pass through the dangerous spots, they only found out that the drones were very close to the dangerous spots when they checked the aerial photos.. These dangers and hidden dangers often cause huge property losses to customers.

A base station shows in the photo, you can see it is very close to the drone, very likely to hit on Therefore, many customers have given us suggestions: Can a long focal length oblique camera be designed to make the flight height of the drone higher and make the flight safer? Based on customer needs, based on D2,we have developed a long focal length version named RIY-D3. Compared with D2, at the same resolution, D3 can increase the flight height of the drone by about 60%.

During the R&D of D3, we have always believed that a longer focal length can have a higher flight height, better modeling quality and higher accuracy. But after the actual working, we found that it was not as expected, compare with D2,the 3D model built by D3 was relatively strained, and the work efficiency was relatively low.

Name Riy-D2/D3
Weight 850g
Dimension 190*180*88mm
Sensor type APS-C
CMOS   a size 23.5mm×15.6mm
Physical size of pixel 3.9um
Total pixels 120MP
Mininum exposure time interval 1s
Camera exxposure mode Isochronic/Isometric Exposure
focal length 20mm/35mm for D235mm/50mm for D3
Power supply Uniform supply(Power by drone)
memory capacity 320G
Data download spped ≥70M/s
Work temperature -10°C~+40°C
Firmware updates For free
IP rate IP 43

2、The connection between focal length and modeling quality

The connection between the focal length and the modeling quality is not easy for most customers to understand, and even many oblique camera manufacturers mistakenly believe that a long focal length lens is helpful for modeling quality.

 The actual situation here is: on the premise that other parameters are the same, for the  building facade, the longer the focal length, the worse the modeling equality. What kind of logical relationship is involved here?

In the last artical How focal length affect 3D modeling results we have mentioned that:

Under the premise that other parameters are the same, the focal length will only affect the flight height. As shown in the above figure, there are two diffent focal lenses, red indicates a long focal lens, and blue indicates a short focal lens. The maximum angle formed by the long focal lens and the wall is α, and the maximum angle formed by the short focal lens and the wall is β. Obviously:

What does this “angle” mean? The greater the angle between the edge of the FOV of the lens and the wall, the more horizontal the lens relative to the wall. When collecting information on building facades, short focal lenses can collect wall information more horizontally, and the 3D models based on it can better reflect the texture of the facade. Therefore, for scenes with facades, the shorter the focal length of the lens, the richer the collected facade information and the better the modeling quality.

 

For buildings with eaves, under the condition of the same ground resolution, the longer the focal length of the lens, the higher the drone flight height, the more blind spots under the eaves, then the worse the modeling quality will be. So in this scenario, the D3 with a longer focal length lens can not compete with D2 with a shorter focal length lens.

3、The contradiction between the flight height of the drone and the quality of the 3D model

According to the logic connection of the focal length and the quality of the model, if the focal length of the lens is short enough and the FOV angle is large enough, no multi-lens camera is needed at all. A super wide-angle lens (fish-eye lens) can collect the information of all directions. As shown below:

 

Isn't it fine to design the focal length of the lens as short as possible?

Not to mention the problem of large distortion caused by the ultra-short focal length. If the focal length of the ortho lens of oblique camera is designed to be 10mm and the data is collected at a resolution of 2cm, the flight height of the drone is only 51 meters.

 Obviously, if the drone is equipped with an oblique camera designed in this way to do jobs, it will definitely be dangerous.

PS: Although the ultra-wide-angle lens has limited use of scenes in oblique photography modeling, it has practical significance for Lidar modeling. Previously, one famous Lidar company had communicated with us, hoping us to design a wide-angle lens aerial camera, mounted with the Lidar, for ground object interpretation and texture collection.

4、From D3 to DG3

The R&D of D3 made us realize that for oblique photography, the focal length cannot be monotonously long or short. The length is closely related to the quality of the model, the efficiency of working, and the height of the flight. So in the lens R&D, the first question to consider is: how to set the focal lengths of lenses?

Although the short focal has good modeling quality, but the flight height is low, it’s not safe for drone’s flight. In order to ensure the safety of drones, the focal length must be designed longer,but longer focal length will affect the working efficiency and modeling quality. There is a certain contradiction between the flight height and the 3D modeling quality. We must seek a compromise between these contradictions.

So after D3, based on our comprehensive consideration of these contradictory factors, we had developed the DG3 oblique camera. DG3 takes into account both the 3D modeling quality of D2 and the flight height of D3, while also adding a heat-dissipation and dust-removal system, so that it can also be used on fixed-wing or VTOL drones. DG3 is the most popular oblique camera for Rainpoo, it is also the most widely used oblique camera on the market.

Name Riy-DG3
Weight 650g
Dimension 170*160*80mm
Sensor type APS-C
CCD size 23.5mm×15.6mm
Physical size of pixel 3.9um
Total pixels 120MP
Mininum exposure time interval 0.8s
Camera exxposure mode Isochronic/Isometric Exposure
focal length 28mm/40mm
Power supply Uniform supply(Power by drone)
memory capacity 320/640G
Data download spped ≥80M/s
Work temperature -10°C~+40°C
Firmware updates For free
IP rate IP 43

5、From DG3 to DG3Pros

RIY-Pros series oblique camera can achieve better modeling quality. So what special design does Pros have in lens layout and focal length setting? In this issue, we will continue to introduce the design-logic behind the Pros parameters.

6、Oblique lens angle and modeling quality

The previous content mentioned such a view: the shorter the focal length, the larger the angle of view, the more building facade information can be collected, and the better the modeling quality.

 In addition to setting a reasonable focal length, of course, we can also use another way to improve the modeling effect: directly increase the angle of the oblique lenses, which can also collect more abundant facade information.

 

But in fact, although setting a larger oblique angle can improve the modeling quality, there are also two side effects:

 

1:Working efficiency will reduced. With the increase of the oblique angle , the outward expansion of the flight route will also increase a lot. When the oblique angle of exceeds 45 °, the flight efficiency will drop sharply.

For example, the professional aerial camera Leica RCD30, it’s oblique angle is only 30 °, one of the reasons for this design is to increase the working efficiency.

2:If the oblique angle is too large, sunlight will easily enter into the camera, causing glare (especially in the morning and afternoon of a hazy day). Rainpoo oblique camera is the earliest to adopts the internal-lens design . This design is equivalent to adding a hood to the lenses to prevent it from being affected by the oblique sunlight.

Especially for small drones, in general, their flight attitudes are relatively poor. After the lens oblique angle and the attitude of the drone are superimposed, stray light can easily enter into the camera, further amplifying the glare problem.

7、Route overlap and modeling quality

According to experience, in order to ensure the model quality, for any object in space, it is best to cover the texture information of the five groups of lenses during flight.

 This is easy to understand. For example, if we want to build a 3D model of an ancient building, the modeling quality of the circle flight must be much better than the quality of taking only a few pictures on four sides.

The more covered photos, the more spatial and texture information it contains, and the better the modeling quality. This is the meaning of flight route overlap for oblique photography.

The degree of overlap is one of the key factors that determine the quality of the 3D model. In the general scene of oblique photography, the overlap rate is mostly 80% heading and 70% sideways (the actual data is redundant).

In fact, it is certainly best to have the same degree of overlap for sideways, but too high sideways overlap will drastically reduce flight efficiency (especially for fixed-wing drones), so based on efficiency , the general sideways overlap will be lower than the heading overlap.

 

Tips: Considering the working efficiency, the overlapping degree is not as high as possible. After exceeding a certain "standard", improving the overlapping degree has a limited effect on the 3D model. According to our experimental feedback, sometimes increasing the overlap will actually reduce the quality of the model. For example, for a 3 ~ 5cm resolution modeling scene, the modeling quality of lower overlapping degree sometimes are better than the higher overlapping degree.

8、The difference between theoretical overlap and actual overlap

Before flight, we set 80% heading and 70% sideways overlap, which is just the theoretical overlap. In the flight, the drone will be affected by the airflow, and the change in attitude will cause the actual overlap to be less than the theoretical overlap.

In general, whether it is a multi-rotor or fixed-wing drone, the poorer the flight attitude, the worse the 3D model’s quality. Because the smaller multi-rotor or fixed-wing drones are lighter in weight and smaller in size, they are susceptible to interference from external airflow. Their flight attitude is generally not as good as that of medium / large multi-rotor or fixed-wing drones, resulting in the actual overlapping degree in some certain ground area is not enough, which ultimately affects the modeling quality.

9、Difficulties in 3D modeling of high-rise buildings

As the height of the building increases, the difficulty of 3D modeling will increase. One is that the high-rise building will increase the risk of drone’s flight, and the second is that as the height of the building increases, the overlap of the high-rise parts drops sharply, resulting in poor quality of 3D model.

1 The Influence of Increasing Overlap on 3D Modeling Quality of High-rise Building

For the above problem, many experienced customers have found a solution: increase the degree of overlap. Indeed, with the increase of the degree of overlap, the model effect will be greatly improved. The following is a comparison of the experiments we did:

Through the above comparison, we will find that: the increase in the degree of overlap has little influence on the modeling quality of low-rise buildings; but has great influence on the modeling quality of high-rise buildings.

However, as the degree of overlap increases, the number of aerial photos will increase , and the time for data processing will also increase.

2 The Influence of focal length on 3D Modeling Quality of High-rise Building

We have made such a conclusion in the previous content:For facade building 3D modeling scenes, the longer the focal length , the worse the modeling quality. However, for the 3D modeling of high-rise areas, a longer focal length is required to ensure the modeling quality. As shown below:

Under the conditions of the same resolution and overlapping degree, the long focal length lens can ensure the actual overlapping degree of the roof and a sufficiently safe flight height to achieve a better modeling quality of high-rise buildings.

For example, when the DG4pros oblique camera is used to do 3D modeling of high-rise buildings, not only can it achieve good modeling quality, but the accuracy can still reach 1: 500 cadastral survey requirements, which is the advantage of the long focal length lenses.

Case: A success case of oblique photography

10、RIY-Pros series oblique cameras

To achieve a better modeling quality, under the premise of the same resolution, it is necessary to ensure sufficient overlap and the large fields of view.For regions with large terrain height differences or high-rise buildings, the focal length of the lens is also an important factor that affects the modeling quality. Based on the above principles, Rainpoo RIY-Pros series oblique cameras have made the following three optimizations on the lens:

1 Change the layout of the lenses

For Pros series oblique cameras, the most intuitive feeling is that its shape changes from the round to square. The most direct reason for this change is that the lenses layout has changed.

The advantage of this layout is that the camera size can be designed to be smaller and the weight can be relatively lighter. However, this layout will result in the overlapping degree of the left and right oblique lenses being lower than that of the front, middle, and back perspectives: that is, the area of shadow A is smaller than the area of shadow B.

As we mentioned before, in order to improve flight efficiency, the sideways overlap is generally smaller than the heading overlap, and this “surround layout” will further reduce the sideways overlap, which is why the lateral 3D model will be poorer than the heading 3D model.

So for the RIY-Pros series, Rainpoo changed the lenses layout to: parallel layout. As shown below:

This layout will sacrifice part of the shape and weight, but the advantage is that it can ensure sufficient sideways overlap and achieve a better modeling quality. In actual flight planning, RIY-Pros can even reduce some sideways overlap to improve flight efficiency.

2 Adjust the angle of the oblique lenses

The advantage of the “parallel layout” is that it not only ensures sufficient overlap, but also increases the side FOV and can collect more texture information of buildings.

On this basis, we also increased the focal length of the oblique lenses so that its bottom edge coincided with the bottom edge of the previous “surround layout” layout, further increasing the side view of angle, as shown in the following figure:

The advantage of this layout is that although the angle of oblique lenses is changed, it does not affect the flight efficiency. And after the FOV of side lenses is greatly improved, more facade information data can be collected, and the modeling quality is of course improved.

Contrast experiments also show that, compared to the traditional layout of the lenses, Pros series  layout can really improve the sideways quality of 3D models.

The left is the 3D model built by the traditional layout camera, and the right is the 3D model built by the Pros camera .

3 Increase the focal length of the oblique lenses

 

RIY-Pros oblique cameras lenses is changed from the traditional “surround layout” to a “parallel layout”, and the ratio of the near-point resolution to the far-point resolution of the photos taken by oblique lenses will also increase.

 

In order to ensure that the ratio does not exceed the critical value, Pros oblique lenses focal length is increased by 5% ~ 8% than before.

Name Riy-DG3 Pros
Weight 710g
Dimension 130*142*99.5mm
Sensor type APS-C
CCD size 23.5mm×15.6mm
Physical size of pixel 3.9um
Total pixels 120MP
Mininum exposure time interval 0.8s
Camera exxposure mode Isochronic/Isometric Exposure
focal length 28mm/43mm
Power supply Uniform supply(Power by drone)
memory capacity 640G
Data download spped ≥80M/s
Work temperature -10°C~+40°C
Firmware updates For free
IP rate IP 43

Previous:

Next:

Return