Learn GIS _ tilt photography technology in five minutes

In this issue, we will study GIS for five minutes, and we will introduce oblique photography technology.

What is tilt photography?

Tilt photography technology is to collect images from different angles such as one vertical and four sides by carrying multiple sensors on the flight platform. We can understand it as an evolutionary photogrammetry technology, which has four more oblique shooting angles than traditional photogrammetry, thus obtaining more information such as side texture.

A collection of oblique images

The collection of oblique images is mainly divided into two processes, one is equipment preparation, the other is route design and real shooting.

Equipment preparation: The equipment for oblique image acquisition includes airplane and oblique camera. An airplane can be a manned airplane or an unmanned aerial vehicle. Manned aircraft are mostly used for large-area tilt photography, such as domestic Yun-12 and Yun -5. Unmanned helicopters can be used for medium-sized operations, such as seven-dimensional aerial survey unmanned helicopters, and multi-rotor UAVs can be used for small-sized operations, such as Peng Hong UAV and DJI UAV. As for tilt cameras, most tilt cameras use five kinds of lenses, such as downward view, forward view, backward view, left view and right view, such as Leica RCD30 tilt camera, four-dimensional vision SWDC-5 tilt camera and Peng Hongwei tilt camera.

Design route and actual shooting: the route design of oblique photography is designed by special route design software, and its relative height, ground resolution and physical pixel size meet the triangular proportional relationship. After the equipment assembly and route planning are completed, aerial photography is carried out to obtain multi-angle images with certain overlap, and the oblique image acquisition part is completed.

Inclined model production

The oblique image obtained by oblique photography can be modeled after image processing. Modeling technology is mainly divided into three categories, they are:

The first kind of tilt photography+airborne laser scanning modeling, that is, tilt photography provides model texture, airborne radar constructs model skeleton, and then generates tilt photography model through moderate human intervention. Common output formats are. obj，。 Max, wait. At present, the data vendors with this modeling technology are: Wuhan Huazheng, Dongfang Daoyou and Zhongke Remote Sensing.

The second kind of tilt photography+manual intervention modeling is also to automatically model the tilt photography data, and then modify it manually by modifying the software. The details of decoration include: skeleton deformation of the model, shading of the texture at the bottom of the building, etc. The modified model results will not destroy the structure of the automated model results. At present, the software adopting this technology includes DP-Modeler of Sky Airlines, etc.

The third automatic modeling of oblique photography is a multi-view image generation model obtained only by oblique photography, that is, a mesh (triangulation) model. At present, the automated modeling software on the market includes Street View Factory, Smart3DCapture, Altizure, PhotoScan, Pix4D, Infinite Bound and so on. The common output formats of this model are osgb, dae, obj, s3c(Smart3D private format), 3mx (lightweight open format) and so on. The process of automatic modeling can be simply described as follows: firstly, through a series of complex operations such as geometric correction and joint adjustment, dense point cloud data with elevation are obtained and refined, then a continuous TIN triangulation network is constructed, and finally a high-scoring image is pasted on the triangulation network, and finally an inclined photographic model is obtained, as shown in the following figure.

What are the advantages of tilt photography modeling technology?

Traditional 3D modeling usually uses 3ds Max, AutoCAD and other modeling software. Based on the information such as image data, CAD plan or photographed pictures, manual modeling is carried out to estimate the outline and height of buildings. The model data produced in this way has beautiful appearance, low deformation rate of local details, but low accuracy, large deviation between texture and actual effect, and a large number of manual participation in the production process, and a long production cycle. Tilt photography technology directly reflects the appearance, position, height and other attributes of ground objects through efficient data acquisition equipment and professional data processing flow, which ensures the real effect and accuracy of surveying and mapping and effectively improves the production efficiency of the model. A small and medium-sized city modeling work that takes one or two years by hand can be completed only in three to five months by oblique photography, which greatly reduces the economic cost and time cost of obtaining three-dimensional model data.

Tilt photography model and

As one of the important sources of 3D GIS data, oblique photography model is increasingly applied to 3D GIS projects. In the application of smart city management system, tourism, scenic spots and other industries, the tilt photography model allows users to observe the ground objects from multiple angles, reflecting the actual situation of the ground objects more truly, making up for the shortcomings based on two-dimensional maps and traditional virtual three-dimensional models.

Tilt photography model can achieve the same GIS application as other traditional three-dimensional model data through a single operation, such as simulating building demolition to meet the application of planning industry; Measure the height, length, area, angle and slope of buildings and apply them to management systems such as water conservancy and energy development; In the 3D scene, you can see the emergency exit on the side of the house, and you can accurately measure any point on the inclined model, such as calculating the visual distance, designing the commanding heights, and sniper schemes. These detailed information around the incident is related to the safety of people and property in emergency operations, and sometimes even plays a decisive role.

Finally, we end this problem with an application case of tilt photography model. In the future development of geographic information industry in China, tilt photography technology will undoubtedly play a more important role!