Unmanned aerial photography. Unmanned aerial vehicles for aerial photography
UAVs for aerial photography for civilian purposes solve the following tasks:
- Shooting weddings and corporate events.
- Protection of personal belongings, houses, detached buildings on the site.
- Delivery and transportation of various valuables.
- The use of devices for hunting and surveillance.
- Help in reconnaissance of difficult roads, in unfamiliar terrain.
- Interior and exterior shooting of facades of houses, cottages, buildings.
- Panoramic shooting of cities, districts of the city.
- Aerial photography of sports competitions (cycling, swimming, ironman, etc.)
You can buy a UAV for aerial photography with the required payloads.
For high-quality video shooting, photos require technical products with certain parameters. For example, aerial photography of commercial real estate requires a drone to have HD cameras in order to create selling views of objects from above. Aerial photography and inspection of pipelines, commercial facilities requires the presence of multispectral cameras, thermal imagers. Of course, the monitoring of mobile, moving objects requires the installation of special target loads, such as cameras with 10,20,30,40x magnification, cameras with the ability to capture and automatically track a target. More than 30 target loads are available for sale in our specialist center.The cost of a drone for aerial photography starts from 80,000 rubles.
For amateur shooting from the air, we recommend buying DJI drones. To solve specialized business tasks, we recommend paying attention to the Geoscan and Supercam series of unmanned aerial vehicles. The price of professional UAVs depends on the configuration, connected target loads, installation of additional software. Copter-type UAVs, the Supercam X6M2 and Geoscan 401 series are also on sale. Read more about their performance characteristics and capabilities in the relevant sections of our website.The cost of a UAV for aerial photography includes:
- The unmanned vehicle itself.
- Ground control station.
- Spare parts.
- Software (already installed).
- Instructions, flight forms.
If you have the task of prompt mapping, surveying gas pipelines, oil pipelines or power lines to determine their condition, our specialists will quickly and within the agreed time do this work for you anywhere in the Russian Federation. Our drones are equipped with a high-quality 24-megapixel SLR camera, a 640*480-pixel thermal imager, and a 10x zoom HD video camera, which allow you to perform planned and perspective aerial photography. To perform the work, our organization concludes an agreement with the Customer for the provision of aerial photography services. For high-precision work, the UAV is equipped with a dual-frequency GPS / GLONASS receiver that uses the most advanced GPS / GLONASS technologies and is able to track satellites even under difficult environmental conditions.
And, of course, we are ready to process the received materials to prepare a photo plan, photo scheme, or perform decryption.
An example of an orthophoto map with an area of 14 km * 14 km, taken from a height of 1.5 km from a Supercam-350 UAV in one day
The essence of aerial photography
Aerial photography of the area is a complex of works that includes various processes from photographing the earth's surface from a flying aircraft to obtaining aerial photographs, photographic schemes or photographic plans of the area taken. It includes:
1. preparatory activities, consisting in the study of the area to be photographed, the preparation of maps, the design of aircraft flight routes and the calculation of aerial photography elements;
2. actually flight and survey work or photographing the earth's surface with the help of aerial cameras;
3. photographic laboratory work on the development of the removed film and the production of positives;
4. geodetic work on the creation of a geodetic base on the ground, which is necessary to correct distortions in aerial photographs that have arisen in the process of aerial photography, to link aerial photographs and to compile photo schemes and photo plans;
5. photogrammetric work, which is carried out both in the field and cameral periods, and is associated with the processing of aerial photographs for the preparation of plans and maps of the surveyed area.
All these processes are closely related to one another and partly overlap. Aerial photography of each object must be carried out by the same organization from the beginning to the delivery of the final product. As a result of these works, contact prints, block layout reproductions of aerial photographs, photo schemes or photo plans are made, compiled according to the data of the geodetic base. All these aerial photographic materials are used in the future to solve a number of issues in the field of forestry and the forest industry.
History of aerial photography
Unmanned aerial photography, as, indeed, history itself, develops in a spiral: in 1858, while flying in a balloon over Paris, Gaspard Felix Tournachon made the world's first aerial photograph, and already in 1887, French photographer Arthur Tramout developed and completed the first unmanned aerial photography with using a kite. Then the ideas of unmanned aircraft developed rapidly in aerial photography, which resulted in the patented "Method and means for photographing landscapes from above" with the help of carrier pigeons of the German pharmacist Julius Neubronner. Moreover, this method was really widely used during the First World War. And only on April 24, 1909, "The first use of a movie camera mounted in a heavier-than-air aircraft" happened when filming a short silent movie clip "Wilbur Wright and his plane." Currently, aerial photography is making another round of its history, becoming unmanned again.
Planned and prospective unmanned aerial photography of the area
In plan shooting, the camera is directed vertically down, at right angles to the ground. In the pictures we see a flat picture (orthogonal projection), reminiscent of an image on geographical maps. With this type of aerial photography, we can determine the relative position of objects on a plane without taking into account their heights. When photographing real estate, we can see those parts of structures that are directed upwards (roofs). This type of shooting is mainly used to create photoplans. A similar product can be obtained using satellite and traditional aerial photography.
In perspective (overview) shooting, the camera is directed at an angle to the horizon. This type of imagery is not possible for satellites and traditional "large aviation". With perspective aerial photography in the pictures we see a three-dimensional picture (axonometric projection): not only the roofs of structures, but also the side surfaces (walls). Thus, we can judge not only the mutual arrangement of objects on the plane, but also their shape. In addition, with perspective shooting, we can determine the height of objects relative to each other. At certain angles of perspective shooting, the horizon line may be present in the frame. In this case, we get the opportunity to see in one picture how the site or structure is inscribed in the surrounding landscape and their relative position with distant objects (distant objects, forests, reservoirs, settlements). Panoramic shots, including full 360-degree panoramas, can be assembled from multiple perspective shots taken with the camera rotated around the vertical axis. Creating aerial panoramas is possible only when using a specially equipped remote-controlled helicopter capable of hovering at a certain height for a long time while shooting adjacent frames.
Stages of aerial photography
The experience gained in the field of using aerial methods in surveys shows their exceptional efficiency compared to traditional methods of collecting information, both in terms of a significant reduction in labor intensity and reduction in survey time, and in terms of the breadth of coverage of various types of information necessary for design. Aerial surveys are carried out in three stages: preparatory, field and cameral.
During the preparatory period, the collection of topographic information available for the survey area and materials from aerial surveys of past years is carried out, on the basis of which the band of variation of competitive route options is substantiated and a project for the production of aerial surveys, field and cameral aerial photogeodetic works is drawn up.
During the field period, the following is carried out: ground geodetic work to create a planned-altitude substantiation of aerial surveys; fixing and marking points of the core network; various types of aerial photography, linking and interpretation of aerial photographs. An important type of aerogeodetic surveys is deciphering - the identification (detection and identification) and disclosure of the content (cognition) of various objects and elements of the terrain from their images in the images, their qualitative and quantitative characteristics, peculiar properties and features.
In the office period, complete processing of the results of geodetic measurements, photogrammetric thickening of the geodetic survey justification using analytical phototriangulation methods, stereophotogrammetric work to obtain information about the relief and make topographic plans and digital terrain models (DTM) in a single coordinate system are performed.
Equipment for unmanned aerial photography
As a rule, modern drone operators use in their daily work a small, up to 3 m span, unmanned aircraft with a conventional, home or studio, CCD-based camera. The most popular "soap dishes" Samsung, Sony, Pentax. Photographs from such devices are generally suitable for drawing up plans and diagrams. SLR cameras provide aerial photographs of much higher quality - here the Canon 550D and its older comrade Canon 5D Mark II are the leaders and the standard. At the same time, of course, large multi-objective systems also find application.
Flight surveys performed by a camera based on a matrix sensor (CCD - matrix) are more reminiscent of the traditional analog method of aerial photography, when all elements of the matrix are simultaneously exposed. In this method, the intrapixel geometry is known and strictly defined. In matrix technology, the current problem is that large matrix gratings are difficult to manufacture. Therefore, they combine: they make large lattices from several small ones. For example, out of four. The four-lens lens forms four separate images, which are transformed into a central projection and automatically joined. Such images are processed according to existing analytical processing programs.
The second main part, and no less important, is the system for determining the position of the UAV / camera in space. In the simplest case, this is an ordinary small-sized GPS receiver with an antenna, such as Ublox. Currently, Russian manufacturers of complexes with UAVs are almost everywhere switching to signal receivers of satellite positioning systems of the combined type GPS / Glonass. Unfortunately, they cannot provide the required accuracy. Therefore, in more expensive and serious devices, an additional high-precision GPS receiver is installed, which allows, during post-processing of raw data, to determine the coordinates of the image center with an accuracy of 5-10 cm.
And if this receiver is used together with terrestrial GPS base stations, then the accuracy of tying frames to coordinates will increase to staggering!!! 5 cm. To perform the survey, base GPS stations are created, the data of which are used to calculate differential corrections when determining the trajectory of the aircraft. To determine the trajectory of the aircraft and refine the angular data of the inertial system, the method of joint processing of GPS data and data of the inertial system is used. Binding images to coordinates, as a rule, is performed using programs written specifically for a specific type of receiver and UAV. The use of this calculation method improves the accuracy of determining both the angular parameters and the location.
The accuracy of GPS/GLONASS navigation and features of UAV automatic control systems allow achieving the following parameters when flying along the aerial photography route:
Transverse offset from the axis of the route - ± 10 m;
keeping the UAV at a given height - ± 15 m;
distance from the projected center of photography to the point of actuation of the camera shutter - ± 5 m;
UAV roll angle change on the route between two images — 10°;
UAV pitch angle change on the route between two images is 6°.
Technology
The result of digital aerial photography of the area are digital aerial photographs, as well as elements of external orientation recorded in flight (linear - Xs, Ys, Zs - coordinates of the center of photography; angular - α, β, γ - orientation of the camera relative to the coordinate axes).
In accordance with the laws of central design, according to which the image of the terrain is built, the aerial negative (aerial photograph) contains a number of distortions, the magnitudes of which are determined by the angle of inclination of the optical axis of the aerial camera and the fluctuation of the terrain. The elimination of these distortions is carried out in the process of their computer photogrammetric processing, and in particular - photographic or digital transformation, called transformation. In this regard, the use of aerial photographs without their preliminary transformation for cartographic (topographic) support of the work performed, including as the basis of a GIS, is limited by the influence of these distortions.
The readings of special instruments and equipment, recorded in the process of aerial photography, ensure the stabilization of the shooting camera in flight or the subsequent determination of the spatial position of aerial photographs in an absolute or relative coordinate system with the aim of their subsequent use in performing photogrammetric work and converting aerial photographs into plans and maps. Such devices include gyroscopes, global positioning systems, equipment for determining the flight altitude, elevations between photography centers, as well as air navigation systems, etc. The availability of these data largely determines the technology of cameral processing of aerial photography materials, significantly affects the efficiency, accuracy of photogrammetric constructions and scope of field work to ensure them.
Route planning
Aerial photography can be areal and linear, in areal photography, in addition to the longitudinal overlap of the images, it is also necessary to observe the transverse overlap. The initial parameters of photography using a drone are the required resolution of the image, the resolution of the aerial camera, the angle of view of the camera lens, and the amount of frame overlap. From this data, flight altitude, drone speed and camera shutter frequency are calculated.
Flight and photography
During the flight, the drone automatically calculates its speed and shutter frequency (frame rate) so as to provide the specified frame overlap. The overlap of UAV images meets the usual requirements for aerial photography and is usually 60% of the frame. The UAV images overlap by 60% in the longitudinal overlap and by 30% in the transverse overlap.
Operational viewing of the results of aerial photography of the area. As a result of the flight, a set of photographs and telemetry data are formed, which include the coordinates of the photographing center, as well as roll, pitch and heading angles.
Stages of processing aerial photographs in photogrammetric software
1) Project creation (name, coordinate system, object height range, placement in the resource system);
3) Import orientation from metadata;
4) Interior orientation (Creating a camera passport);
5) Import of exterior orientation;
6) Formation of block layout according to external orientation;
7) Network measurement (UAV triangulation machine, tie point machine with specified parameters, measurement of reference substantiation), control;
8) Network adjustment (calculation of systematics, self-calibration, control measurements), control;
9) DEM creation (point cloud, TIN, breaklines, DEM, contours), control;
10) Image transformation, control;
11) Work with orthophotos (cuts, brightness equalization, cutting into sheets), control;
12) (Optional) Stereovectorization to create 3D maps and 3D models;
13) (Optional) Create 2D maps.
There are three types of data processing: affine transformation of frames to create an orthophotoscheme of flat areas, full orthorectification of frames to create an orthophotoscheme of territories with a pronounced relief, full orthorectification of frames to create an orthophotomap with the fulfillment of geodetic scale requirements.
Affine Frame Transformation to Create an Orthophotoscheme of Plain Territories
The program determines common points (from 50 to 1200) between each pair of images. After that, an equation is solved, which includes information on all images, to find the minimum RMS (standard deviation) between all vectors connecting common points. Simply put, an elastic band is stretched between each pair of points, and all frames line up so that the total tension of the elastic bands is minimal. In this case, the frame can only be transformed affinely, i.e. any straight line is displayed only in a straight line.
Orthophotos from an unmanned aircraft
The program determines common points (from 50 to 1200) between each pair of images. After that, the full photogrammetric equation is solved with the definition of the terrain with an accuracy of 10 pixels. At the same time, the coordinates of the photographing center and the orientation parameters (roll, pitch, heading) are specified.
In accordance with the calculated data, all frames are orthorectified and the result is projected onto a plane. Binding to real data is carried out according to the data existing in publicly available cartographic resources. For example, according to Google Earth. The accuracy of these data in Russia is about 6 meters.
UAV orthophotos
The program determines common points (from 100 to 3000) between each pair of images. After that, the full photogrammetric equation is solved with the definition of the terrain with an accuracy of 2 pixels. At the same time, the coordinates of the photographing center and the orientation parameters (roll, pitch, heading) are specified with high accuracy.
In accordance with the calculated data, all frames are orthorectified and the result is projected onto a plane. Linking to real data is carried out based on the results of ground justification, which includes at least one point for every 10 frames or at least 10 points for one orthomosaic. Half of these points are used for anchoring, the other half for confirming accuracy requirements. The accuracy of relief formation in this case meets the requirements of the corresponding scale.
The result of the work are geotiff files with an accuracy corresponding to the given scale. The geotiff format includes two files - orthorectified aerial photography and digital elevation model (DEM - digital elevation model), which can be opened in any GIS program, such as ArcGis or GlobalMapper. On enabled DEM, it is possible to form relief isolines with any height difference.
3D terrain model
Based on the results of aerial photography, the relief is restored from photographs from the UAV. Together with DEM, it is possible to generate relief along isolines with the required accuracy. The standard format is ArcGis vector lines that can be imported into any mapping system.
The company's specialists can produce the result in almost any required format. To do this, you need to specify the program in which the result is supposed to be used.
It is also possible to make a transition to the local coordinate system from WGS. When performing a ground justification, we can perform a survey of coordinates on the symbols of the GGS (state geodetic network), then the work can be immediately performed in the local coordinate system without conversion and the corresponding loss of accuracy.
Calculation of aerial photography parameters by an unmanned aerial vehicle
k. s.-x. n., Assoc.
(SPbGLTA, St. Petersburg, Russia)
In article calculation of parameters for aerial photography planning by digital cameras with use of unmanned aerial vehicles is presented.
Aerial photography by unmanned aerial vehicles is becoming more and more widespread, which leads to the use of modern digital cameras, both specially designed and standard, in combination with UAVs. Pictures taken with a digital camera can be processed immediately after shooting. The use of aerial cameras (AFA) with UAVs belonging to the Micro and Mini class according to the international classification is impossible, since they have a rather large weight and size, and also have a number of disadvantages. For example, to obtain aerial footage, the film must be developed and scanned. At the same time, the main disadvantage of digital cameras is the low resolution of the obtained images compared to the images obtained by AFA with a frame size of 23x23 cm.
To plan aerial photography, it is necessary to calculate the main parameters. When calculating the parameters of aerial photography by an unmanned aerial vehicle equipped with a digital camera, the following initial data will be required, which are summarized in Table 1.
Table 1
Initial data for calculating the parameters of aerial photography
|
Index |
Unit rev. |
Designation |
|
|
Plot dimensions | |||
|
Terrain pixel size | |||
|
Image side dimensions | |||
|
Longitudinal overlap of images in a route | |||
|
Cross overlap | |||
|
UAV speed during aerial photography | |||
|
Recording time of information in a digital camera |
When conducting aerial photography with digital cameras, in order to obtain images with the required pixel size on the ground, it is necessary to shoot at a certain height. The resolution of digital images is usually characterized by the number of dots per inch - dpi (from the English dots per inch) and the pixel size on the ground - GSD(from English. Ground Sample Distance). The flight altitude is calculated using the following formula:
Hfloor- flight altitude, m;
GSD- size of one pixel on the ground, pixel resolution, m/px;
lX- camera image size, px.
Since digital images have the shape of a rectangle, it is recommended to place the camera with the long side along the direction of shooting during shooting, as this will increase the basis of photography, and, therefore, improve the photogrammetric intersection (Fig. 1).
Rice. 1. Relative location of images in the route
On fig. 1 clearly shows that if the aspect ratio of the image is 2:3, then the location of the image with the long side along the shooting direction allows you to increase the basis of photography ( b) by 1.5 times. Accordingly, the time increases by 1.5 times TRF to record information from a digital camera to a drive. Therefore, the minimum distance between frames bmin for a digital camera primarily depends on its technical characteristics and the speed of the unmanned aerial vehicle V.
Overlaps between adjacent images of the same strip are called longitudinal ( px) . Both too small and too large overlaps are unsuitable for production. For stereoscopic viewing of the filmed area, it is sufficient to have a longitudinal overlap of 50%. However, the edge parts of the aerial photographs have a number of defects, so it is not possible to view the entire area of the aerial photograph stereoscopically. Large overlaps are also unacceptable, as this drastically reduces the volume of the image. Nearly 100% overlap produces two identical aerial photographs that do not have a stereoscopic effect. Overlaps between adjacent images in flat shooting conditions should be within 56-69%, in mountainous conditions - up to 80-90%. Thus, the distance between shots ( B) taking into account the longitudinal overlap is determined by the following formula:
But when conducting aerial photography using UAVs, in order to provide the necessary longitudinal overlap between adjacent images of the same route (Fig. 2), the following restriction must be observed:
Rice. 2. Scheme of aerial photography of the site
Route width on the ground ( LM) depends on the frame height ( ly) used in conjunction with a UAV digital camera.
The overlaps between routes are called transverse ( Py). Their value is usually set within 20-40%. You can determine the distance between adjacent routes using the formula:
Section length Dx equal to the length of the average route in the longitudinal direction from the left edge of the first aerial photograph to the right edge of the last aerial photograph. Lot width Dy measured in the transverse direction in the middle from the upper side of the aerial photograph of the first route to the lower side of the aerial photograph of the last route. Thus, the number of shots in the route Nsn is defined as the ratio of the segment length to the distance between images, taking into account the longitudinal overlap.
The number of routes will be more per unit of the ratio of the section width to the distance between adjacent routes.
Number of shots per area Nuch is defined as the total number of images along all aerial photography routes.
When evaluating the effectiveness and economic feasibility, it is important to determine how much time it will take for aerial photography of the site. tuch. This will also allow you to assess what period of time is best to carry out these works.
As a result, the following conclusions can be drawn:
1. Compared to traditional AFA, digital cameras are inferior in terms of technical indicators (in image resolution), which increases the number of routes and images in them during aerial photography, and as a result complicates further processing of the received materials.
2. When carrying out UAV aerial photography, in order to ensure overlap between images, it is necessary to take into account the technical characteristics of digital cameras, and it is also desirable to choose a UAV with a glider aerodynamic configuration that allows you to fly at a fairly low speed.
3. UAVs can be very effectively used for surveying small areas, for example, for compiling cadastral plans for small areas and for operational monitoring of the situation in problem areas.
This work was supported by a grant from the President of the Russian Federation for young Russian scientists MK-2617.2010.5.
Bibliographic list
1., Vavilov aerial photography and aviation. Assessment of the quality of aerial photography: Guidelines for laboratory studies. L.:LTA, 1s.
2. Nikiforov unmanned aerial vehicles for inventory, mapping and management of landscape gardening facilities.//Forests of Russia in the XXI century. Materials of the first international scientific and practical Internet conference. - St. Petersburg: SPbGLTA, 2009. No. 1, p. 248-251.
3. Nikiforov cameras used for aerial photography by unmanned aerial vehicles in forestry // Forests of Russia in the XXI century. Materials of the first international scientific and practical Internet conference. - St. Petersburg: SPbGLTA, 2010. No. 4, p. 65-70
4., Kadegrov Russian-made aircraft used in the forest industry // Forests of Russia in the XXI century. Materials of the third international scientific and practical Internet conference. - St. Petersburg: SPbGLTA, 2010. No. 3, p. 144-149.
5., Munimaev of foreign unmanned aerial vehicles // Proceedings of the forest engineering faculty of PetrSU. - Petrozavodsk.: Publishing House of PetrGU, 2010. No. 8, p. 97-99.
6. Basic provisions for aerial photography carried out to create and update topographic maps and plans of the State Committee for Industries. –M.: Nedra, 1982, -16 p.
7. Dry methods in forestry and landscape construction: Textbook. - Yoshkar-Ola: MarGTU, 20s.
We are sure of one thing: high price does not always mean high quality.
We will plunge into the industry and find out how drones will perform when filming.
This study uses terms and specific jargon, but they will not prevent you from getting to the point. In this study, the data was processed in DroneDeploy and a high alignment accuracy of 9 cm was obtained.
Description
Topographic survey is an integral part of all projects in the field of land management.
In this example, we will consider a piece of land on which a new village was to be built. Prior to commencement of work, it was necessary to carry out an accurate topographic survey for several reasons:
- Carry out initial land development to design water flow for drainage.
- Conduct a topographic survey of the floodplain of the adjacent river to prevent possible floods.
If you are going to start your own drone department, be prepared for it to be a major investment, and as a result, more time may be spent on the project.
Geodesy 101
Conventional topographic surveying requires the collection of point coordinates on a predetermined grid. In this case, a grid of 150x150 cm was used:
Measurements were made every 150 centimeters, at each intersection:
A total of 1632 coordinates were collected on a survey area of 34.5 ha.
Without the drone shooting at 20 points/hour (1 point, every 3 minutes), the data collection would take approximately 82 hours.
82 hours of traditional surveying means that an engineer has to wait at least a week to start processing the data. Then it will take another 3-4 days before the work is done.
By doing the same UAV survey, the field team was able to provide the developer with a faster view.
First of all, it was not necessary to collect 1600 points over the entire area. Instead, it took only 10 ground markers to be surveyed, located in the field of view:
For larger projects, Ground Control Points (GCPs) are best placed on a grid.
10 ground marks or 1632 points:
10 reference marks can be made in 1-2 hours.
Those who are familiar with photogrammetry know that points collected from the surface of the water are unacceptable for use in such surveys.
After completing the GCP collection, points were collected by the traditional method in standing water areas - a combination of the two methods described above.
End collected points:
As a result, we got 117 points (10 GCP + 107 in areas with standing water).
Shooting time:
Theoretically: 10 ground tags + collecting points = 1-2 hours
Actual: 117 points (10 GCP + 107 in standing water areas) at a collection rate of 20 points/hour = 5.85 hours
Traditional method: 1.632 points at a collection rate of 20 points / hour = 81.6 hours
Within an hour, all actions with the UAV were completed, including assembly, pre-flight checks, launch, landing, disassembly and initial stitching of the map.
Thus we got:
UAV (1 hour) + collecting points (5.8 hours) =
Total field work time: 6.8 hours
Comparison:
34.5 ha/ UAV field work = 6.8 hours
34.5 ha/ conventional field work = 81.6 hours
Total savings: 74.8 hours
Data analysis
After field work, the data obtained require careful processing. First, ground marks are processed, while their position must be fully adjusted.
Next, the corrected points (.las file) must be exported to form the basis of the topographic data. However, the large number of points in the .las file means that the initial topographic contours come out quite rough:
The contours must be smoothed in order to subsequently create a consistent line without losing accuracy. Otherwise, the data obtained is unusable.
After 2 days of additional processing, the resulting topographic contours became accurate within 9 centimeters, both horizontally (X, Y) and vertically (Z):
General terms of the project:
UAV Method::
Field work (6.8 hours) + data processing (24 hours) =
30.8 hours (about 4 days)
Usual method:
Field work (81.6 hours) + Data processing (24 hours) =
105.6 hours (about 13 days)
Using drone technology, the engineer got the final topographic view in about 75 hours.
According to the data obtained, it turned out that:
1. Additional land development is required to build runoff drainage in low-lying areas where water is retained.
2. Workers will now be able to effectively predict and plan dates for the construction of roads, houses, etc. - which will help to complete the work on time.
3. An engineer has learned about inexpensive and cost-effective UAV surveying and plans to use this method again to conduct a final "embedded" topographic survey in the coming weeks.
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