Digital mapping system review - VisionMap

Surveying technical

Digital mapping system review by Dr. Yuri Raizman, VisionMap

The A3 Edge camera provides a complete solution together with the A3 LightSpeed Processing System. The latter automatically performs aerial triangulation and produces orthophotos, stereo pairs and DSM from all A3 cameras. This article reviews the applicability of data captured by A3 Edge for nationwide coverage orthophoto generation, mapping and 3D modeling.

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isionMap, a leader in aerial survey equipment and software development for photogrammetry and mapping, has developed and successfully implemented a new innovative aerial survey and mapping system, the A3. The A3 aerial systems with LightSpeed ground processing system are used worldwide and are said to provide superior image quality and higher aerial survey productivity. Over the last four years, more than thirty A3 systems have been delivered to customers. In mid-2013, production of the newest camera model, the A3 Edge, began. In addition to the new camera model, the new gyro stabilised mount SOMAG VSM 500 was developed in collaboration with the German company SOMAG. The mount serves to further improve image quality and aerial survey productivity. VisionMap is constantly working on the improvement of existing software and on new developments. Two new versions of the main LightSpeed and related programs were released in 2013. Additionally, two new programs were developed, FlightViewer and TopoFlight. FlightViewer is designed for quick viewing of images during or immediately after the flight without pretreatment, and TopoFlight is designed for more efficient and accurate planning of aerial survey flights.

New model The new camera model, the A3 Edge, is briefly characterised by the following parameters: z

z

Ground resolution of 5 cm can be obtained from a height of 2000 m, and from a height of 10 000 m the ground resolution is 25 cm. Geodetic accuracy of the final products without control points and without GPS ground stations varies

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Fig. 1: Example 1 – RGB image.

Camera model

A3

A3 Edge

Weight (kg)

38

42

50*60*60

50*60*60

300

300

RGB or RGB+NIR

RGB and RGB+NIR

Colour depth (bit)

12

12

Image motion compensation

Yes

Yes

Max FOV (°)

106

108

Vertical images

Yes

Yes

Oblique images

Yes

Yes

Pixel size (μ)

9,0

7,4

4006 х 2666

4864 x 3232

62 000 x 7900

78 000 х 9600

480

718

7–8

6–7

-15° – +55°

-15° – +55°

Size (cm) Focal length (mm) Colour

CCD size (pixel) Image size (pixel) Image volume (Mpixel) On-board storage capacity (hour) Operating temperature (°С)

Table. 1: Technical characteristics of the A3 and A3 Edge cameras.

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between 20 – 50 cm depending on ground resolution. z

Aerial survey productivity – up to 11 000 km2 per hour, depending on the altitude and the ground speed of the aircraft.

z

Ground processing productivity – up to 9000 km2 orthophoto per day depending on the ground resolution of the images.

z

Automatic aerial survey and ground processing.

z

Virtually no need for field geodetic work.

Table 1 summarises the main technical characteristics of the A3 and A3 Edge cameras.

289 knots. Increasing the altitude and the speed, will also increase the aerial survey productivity. For GSD = 15 – 25 cm the permissible orthophoto angle of 65° was used for the aerial survey productivity calculations. It should be noted that this angle corresponds to 20% of the side overlap for standard analog cameras like RC30 with a focal length of 150 mm. Also, for the calculations, the forward overlap of 55% and the side overlap of more than 55% were used. This aerial survey productivity was calculated for the A3 Edge camera with a gyro stabilised mount.

The wide field of view angle of the camera and, subsequently, its impact on the aerial survey coverage on the ground, is illustrated in Fig. 4. Fig. 4 shows that at the maximum opening of the field of view angle, the aerial survey productivity of the A3 Edge is several times greater than that of other aerial survey cameras.

Example: Mapping South Africa Suppose that our goal is to create colour orthophoto coverage with ground resolution of 25 cm over the entire territory of South Africa. At our disposal is one A3 Edge camera with the LightSpeed ground processing system,

The main differences and advantages of the A3 Edge camera as compared to the A3 model are as follows: z

A new generation of CCD provides superior image quality.

z

Only a CCD built-in electronic shutter is used.

z

The high resolution CCD may improve ground resolution from a given flight altitude or improve the image quality.

z

The maximum off-nadir angle for high ground resolution (3 – 5 cm) and sufficiently high ground speed is increased up to 54°.

z

Improved image stabilisation during rotation of the telescopes improves image quality.

Figs 1, 2 and 3 are examples of high quality images in different spectral bands They were obtained by the A3 Edge camera from a flight altitude of 2225 m with a ground resolution of 5,5 cm. Fig. 1 is a common colour image (RGB), Fig. 2 is an infrared image (NIR, in grey colors) and the Fig. 3 is a colour infrared imagery (CIR). Figs 1 and 2 are images of the same part of the Earth's surface and received simultaneously by two telescopes of the A3 system in different parts of the spectrum. Fig. 3 is a composite of Figs. 1 and 2.

Fig. 2: Example 2 – NIR image.

Orthophoto ground resolution (cm)

All cameras in the A3 family mapping systems are said to be characterised by very high aerial survey productivity. Table 2 presents the parameters and productivity of aerial survey for the A3 Edge camera and the King Air B350 aircraft. The parameters for the King Air B350 are calculated with an acceptable flight altitude of 30 000 feet and a cruising speed of

22

20

25

4,17

8,33

12,50

16,67

20,83

5500

11 000

16 600

22 100

27 700

160

200

235

289

289

25

45

65

65

65

Distance between flight liens (m)

700

2600

6100

8200

10 200

Aerial survey productivity (km2/hour)

210

985

2600

4300

5400

Ground speed (knot)

130

160

170

215

260

15

25

38

42

44

Distance between flight liens (m)

420

1400

3300

4900

6400

Aerial survey productivity (km2/hour)

100

420

1000

2000

3100

Permissible orthophoto angle 2 (deg) RGB+NIR

15

Altitude (m)

Permissible orthophoto angle 2 (deg)

High aerial survey productivity

10

Image GSD (cm)

Ground speed (knot)

RGB

5

Table 2: Parameters and productivity of aerial survey for the A3 Edge camera and the King Air B350 aircraft.

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and King Air 350ER aircraft that can fly at an altitude of up to 35 000 feet with ground speed of 300 knot. The following picture presents a real flight plan for the implementation of such a project. This project is designed using the TopoFlight flight planning program, with the following parameters: z

Average flight altitude ASL – 31 000 feet

z

Ground speed – 289 knot

z

Full image coverage – 1 364 000 km2

z

Full orthophoto coverage – 1 301 000 km2, which corresponds to the entire area of South Africa which is 1 221 037 km2

z

Image GSD – 21 cm

z

Orthophoto resolution – 25 cm

z

Distance between flight lines – 9000 – 11 000 m (depending on the flight altitude and ground height)

z

Forward overlap – 55%

z

Side overlap – 58%

z

Orthophoto angle (2) – 65° (corresponds to 20% side overlap for analog camera RC30 with focal length of 150 mm).

Fig. 3: Example 3 - CIR image.

The entire area of South Africa is then divided into four regions. After the flight planning calculations for each region, the results outlined in Table 3 were obtained. To cover the whole territory of South Africa by aerial survey using one King Air 350ER aircraft and one A3 Edge camera, 189 flight lines and 275 hours of flight time are needed. Assuming the duration of 5 hours for a flight day, only 55 flight days will be needed to cover the entire territory of South Africa. The LightSpeed ground processing system is used for automatic image processing. The system automatically performs the following processes: aerial triangulation and adjustment, DSM

Fig. 4: At the maximum opening of the field of view angle, the aerial survey productivity of the A3 Edge is several times greater than that of other aerial survey cameras.

Full coverage (km2)

Orthophoto coverage (km2)

Total length (km)

Flight lines

Aerial survey productivity (km2/hour)

Total flight (hour)

Total flight (day)

Region 1

328 386

310 736

33 155

56

4923

67

14

Region 2

373 678

358 588

37 577

41

4996

75

15

Region 3

270 265

255 088

28 638

36

4776

57

12

Region 4

391 746

376 736

38 885

56

5061

77

16

1 364 075

1 301 148

138 255

189

4939

275

55

Area

Total

Table. 3: Results from the flight planning calculations for each region.

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(digital surface model) creation and orthophoto production. The system provides very high processing productivity. For example, processing all the images resulting from this aerial survey flight and producing the final products in the form of colour orthophoto with a resolution of 25 cm for the entire country will require a total of 210 days of automatic system operation (6250 km2 per day of orthophoto). This result suggests a ready DEM (digital elevation model). If the DTM's creation is also necessary, the duration of automatic operation of the system will increase by 30%, to 280 days. Some additional time maybe required for some manual or semi-automatic operations like DSM to DTM filtering and QC.

Fig. 5: The entire area of South Africa is divided into four regions.

Conclusion The introduced system includes the A3 Edge digital mapping aerial camera and LightSpeed ground processing system. The main advantages of the system are: z

z

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The highest aerial survey productivity, expressed in tens thousands of square kilometres of aerial survey a day. The highest ground processing

productivity, expressed in thousands of square kilometres orthophoto a day. z

High automation of all processes.

z

The ability to obtain vertical and oblique images by a single camera in one flight.

z

The low weight and small dimensions of the camera allow its use on virtually any type of the aircraft.

z

High ground sample distance from high flight altitude.

z

A variety of capture techniques makes this system universal and indispensable for the mapping of large areas, and for building 3D models of cities.

Contact Dr. Yuri Raizman, VisionMap, [email protected] 

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