1: UAV technology drives the upgrading of surveying and mapping technology and efficiency improvement
Many people have established a connection between the rapid development of unmanned aerial vehicle technology, especially the popularization of consumer-grade unmanned aerial vehicles, and the development of tilt photogrammetry technology. They take it for granted that: the development of UAV technology will inevitably drive or promote the significant improvement of surveying and mapping technology and efficiency. In fact, people just think too much!
Tracing back, aerial tilt photogrammetry technology is not a new technical method, nor is it applied in engineering survey due to the popularity of unmanned aerial vehicles. In the past 20 years, aerial photogrammetry methods and technologies have been widely used in various domestic highway, railway and large-scale topographic mapping projects. Moreover, in order to further improve the accuracy of photogrammetry in elevation, laser radar scanning (Lidar) is also added. Therefore, the wide application of tilt photogrammetry technology is earlier than unmanned aerial vehicles, which has little to do with the development and popularization of unmanned aerial vehicles.
2: UAV measurement accuracy and efficiency are higher
Compared with the aerial tilt photogrammetry method implemented by manned aircraft in the past, the convenience of using unmanned aerial vehicle is mainly reflected in the time period of route application and approval. In the past, when manned aircraft flew, it often required a longer route application approval procedure. However, due to the low flight altitude, unmanned aerial vehicles did not need to apply for a special route in the early stage, flying casually (but now flying casually may have been suspected of breaking the law).
Some people say that when using UAV photography, the height from the ground is lower, and the accuracy of obtaining results is naturally higher. This is not necessarily the case. Although in principle, the lower the flight height, the higher the accuracy of oblique photography, the fact is that the manned flight mode can carry large-scale and professional laser radar equipment, however, the elevation accuracy obtained by laser scanning is naturally one order of magnitude higher than that of photographic analysis. At present, for all kinds of engineering survey and design tasks at all levels, both methods can meet the accuracy requirements of 1:500, 1:2000, etc.
But don’t forget, due to the low flying height of unmanned aerial vehicles, the ground width of one shot is narrower, so the number of reciprocating flights required for the same task increases exponentially. In addition, due to the limitation of battery capacity, common multi-rotor unmanned aerial vehicles can only fly for about 15-20 minutes. For long-distance, large-area highway, railway and other engineering surveying and mapping tasks, it can be imagined that its efficacy must be limited.
3: as soon as the UAV flies, there will be achievements such as digital topographic map
There is also a more important “pit”-due to professional limitations and publicity emphasis, many people mistakenly believe that as long as unmanned aerial vehicles fly over, three-dimensional data and digital topographic maps can be automatically generated. Wrong!
The way of using unmanned aerial vehicle changes only the way of carrying equipment and aircraft, and does not change the fundamental principle and technical route of tilt photogrammetry. The process and process of obtaining the ground elevation by analyzing the stereopair (I .e. aerial triangulation), collecting the terrain feature lines one by one through manual means, manual identification of the surface structure contour, manual editing, etc, there is no substantial change. Moreover, the ground control point, which is necessary to control the accuracy of tilt photogrammetry, is still necessary to adopt UAV mode, and must be manually laid on site. At the same time, it is still indispensable for on-site reconnaissance, investigation, supplementary testing and other work within the measurement range.
Therefore, for an engineering design unit, if you want to independently get through the processes of UAV tilt photogrammetry and real-life modeling, you should first make preparations to build a huge and familiar with relevant professional software, master the preparation of the data processing business team.
4: real-life modeling effect is very cool
At present, another purpose of many projects to carry out UAV tilt photogrammetry is to provide basic data for engineering real-scene modeling. However, combined with the above case II and the actual engineering practice of the author and other teams, things are far from as simple as propaganda and imagination.
The authors and other teams are using the current avant-garde UAV equipment (MD-1000) to collect data and use a professional software to form a three-dimensional real-life model of an existing Expressway. When browsing from the perspective of the air, the effect is quite good. The expressway, road environment and surrounding buildings are all displayed one by one, with strong stereoscopic impression.
However, when we lower the height of the browsing viewpoint and fall near the ground or the height of the driver, the effect we see is completely different, which can even be described as “horrible. Hanging trees, incomplete signs…
Although using different camera resolutions will have a certain impact on the effect of real-scene modeling, the overall situation is: The view from the air is really good, but when changing the view height, the effect cannot bear to look directly. However, the ground perspective is worthy of attention in engineering design and simulation analysis. After all, road facilities serve for vehicles and pedestrians on the road, not for looking at from the perspective of air planes.
5: real-life modeling with xxx software is fully automatic
Some people advertised that “real-life modeling with a professional software is automatically completed by the software”, which is also true. However, the automatically generated real-life model is “unbearable to look directly at” from the ground perspective “. Can the effect of the real-scene model be improved? Methods are available, but only through a large number of manual editing and interactive processing. The following video demonstrates that through some software tools, each house and facility in the real-life model is monolitized one by one, and then on each side of each model, the mapping process and specific operations are performed separately.
Some people may say, “No! What I see in the promotion of so-and-so BIM software is better?!” The reason may often lie in two aspects, one is that people only show you the browsing effect of the aerial perspective; The other is that people spend a lot of manpower and time behind them, edit the secondary processing of the model. However, the workload behind these tasks is often no less than completing an engineering design task.
6: real-life modeling results-useless
Like the author’s team, many people have always hoped to use the real-life modeling results in engineering design to produce practical value. However, after a lot of tossing and trying, they all found that “this thing is really ‘useless to see ‘!” Until today, what you can see in various occasions is still just the display and browsing of the real-scene modeling results of the project, without directly using the real-scene model to carry out the engineering design, or use real-life model as the application case of basic data of engineering design. Looking back, everyone found that maybe this was a dead end.
As we all know, in the survey and design of roads, railways and other projects, route design and engineering quantity calculation must be carried out based on “bare surface”, and all kinds of surface attachments (types, attributes, quantity and other information) to obtain the number of project Demolition. However, due to the inability to distinguish the ground, vegetation and ground objects, the results of real-scene modeling are not even worth the value of a digital topographic map for engineering design, in addition to “browse and show” from the air perspective “.
This is precisely determined by the principles and methods of real-scene modeling. Although the point coordinates and elevation information of the ground, ground objects, facilities and so on can be obtained through the oblique photogrammetry technology, computer software still cannot automatically and accurately identify which ground is, which vegetation is, which are houses and structures.
This is precisely determined by the principles and methods of real-scene modeling. Although the point coordinates and elevation information of the ground, ground objects, facilities and so on can be obtained through the oblique photogrammetry technology, computer software still cannot automatically and accurately identify which ground is, which vegetation is, which are houses and structures.
Someone may ask, “so many engineering management enterprises are playing unmanned aerial vehicles. Have they stepped on the ‘pit?” Based on some recent research meetings, the author and others have learned that the application of unmanned aerial vehicles by engineering management enterprises mainly focuses on engineering and line inspection, etc. These applications focus on real-time acquisition of unmanned aerial vehicles, the application of synchronous video transmission has nothing to do with tilt photography.
