4. Experiments

The characteristics of the cameras and fisheye lenses, which were chosen for the application, are given below.

Nikon Coolpix8700 digital camera has 8 megapixels resolution and CCD sensor. The 8x optical Zoom-Nikkor lens (f/2.8 – 4.2) offers a focal range of 8.9–71.2 mm [83]. Nikon FC-E9 fisheye lens: focal length of the camera's lens reduced to x0.2. Provides approximate 183� (COOLPIX 5700)/190� (COOLPIX 5400) view angle [83].

iPhone 4S camera has 8 megapixels resolution and CMOS sensor. Its focal length is 35 mm [84]. Olloclip 3 in one fisheye lens: The Olloclip is a device providing three different lens options for iPhone, these are wide-angle, fisheye and macro. The Olloclip with the fisheye lens acquires 180� field of view [85]. Table 1 shows technical specifications of the cameras used in the application.

The Olloclip 3 in one was mounted on the iPhone 4S. Images acquired with iPhone 4S and Olloclip 3 in one fisheye lens combination were captured with a focal distance of 4.28 mm. Images have 3264 � 2448 pixels and 1.4 μm pixel width.

The calibration field used in this study is a satellite antenna having 150 cm diameter with 112 control points on it. It was chosen since it has a smooth digital surface model and it is geometrically similar to the lens surface model. In this way, the analysis of the errors caused by the geometry of the objective and a balanced distribution of the depth differences over the image acquisition line on the surface model is accomplished. Point location accuracy is approximately 30–35 μm. In order to get the determined point location accuracy, a geodesic Wild T3 theodolite was chosen for direction measurements. In total, five serial measurements were


Notes: \* These are the values obtained after separate calibrations performed before the application in PI3000 software for iPhone 4S and Nikon Coolpix8700 cameras used in the application. The pictures in the resolution of 3264 � 2448 are taken in this focal length.

Table 1. Technical specifications of the cameras.

made horizontally and vertically with Wild T3 [86]. Used calibration field is complying with self-calibration model, which is a dish antenna model. Figure 7 shows the images of the calibration field taken by the two camera-lens combinations. The images of the calibration field were taken with the minimum focal length of the each camera without zooming.

The application benefits from the comparison made over iPhone 4S Olloclip 3 in one camera fisheye lens combination with Coolpix8700 camera FC-09 fisheye lens combination in terms of equidistant fisheye model [Eq. (7)] which gives the best result in bundle block adjustment. In the application, the calibration values derived from equidistant fisheye model for iPhone 4S Olloclip 3 in one camera fisheye lens combination and Coolpix8700 camera FC-09 fisheye lens combination are compared. Eqs. (8) and (9) use A1, A2, A3, B1, B2, C1, C2 coefficients as calibration parameters. Nine of 112 control points are considered passing points, while 103 of them are full control points. Thirteen images of calibration field were taken by iPhone 4S Olloclip 3 in one

Figure 7. Image of calibration field (Left picture: iphone 4S camera with Olloclip 3 in one; right picture: Nikon Coolpix8700 camera with Nikon FC-E9 fisheye lens).

camera fisheye lens combination from different locations taking into consideration free network adjustment rules. The same procedure was also applied for Coolpix8700 camera FC-09 fisheye lens combination. After then, the two-dimensional image co-ordinates of 112 control points for 13 images were measured in Pictran D software for iPhone 4S Olloclip 3 in one camera fisheye lens combination. The same procedure was also applied for Coolpix8700 camera FC-09 fisheye lens combination. The measurements of the two-dimensional image co-ordinates in Pictran D software are shown in Figure 8.

made horizontally and vertically with Wild T3 [86]. Used calibration field is complying with self-calibration model, which is a dish antenna model. Figure 7 shows the images of the calibration field taken by the two camera-lens combinations. The images of the calibration

These are the values obtained after separate calibrations performed before the application in PI3000 software for iPhone 4S and Nikon Coolpix8700 cameras used in the application. The pictures in the resolution of 3264 � 2448 are taken

Image resolution 3264 � 2448 (8.0 MP) 3264 � 2448 (8.0 MP) Focal length\* 4.324602 mm 9.027620 mm Pixel size\* 1.4 µm 2.7 µm Digital zoom values Up to 5� Up to 4� Aspect ratio 4:3 4:3; 3:2 LCD size 3.5<sup>00</sup> 1.8"

iPhone 4S Nikon Coolpix 8700

' sensor size CCD 2/3<sup>00</sup>

The application benefits from the comparison made over iPhone 4S Olloclip 3 in one camera fisheye lens combination with Coolpix8700 camera FC-09 fisheye lens combination in terms of equidistant fisheye model [Eq. (7)] which gives the best result in bundle block adjustment. In the application, the calibration values derived from equidistant fisheye model for iPhone 4S Olloclip 3 in one camera fisheye lens combination and Coolpix8700 camera FC-09 fisheye lens combination are compared. Eqs. (8) and (9) use A1, A2, A3, B1, B2, C1, C2 coefficients as calibration parameters. Nine of 112 control points are considered passing points, while 103 of them are full control points. Thirteen images of calibration field were taken by iPhone 4S Olloclip 3 in one

Figure 7. Image of calibration field (Left picture: iphone 4S camera with Olloclip 3 in one; right picture: Nikon

field were taken with the minimum focal length of the each camera without zooming.

Sensor CMOS 1/3.2<sup>0</sup>

40 Smartphones from an Applied Research Perspective

Table 1. Technical specifications of the cameras.

Coolpix8700 camera with Nikon FC-E9 fisheye lens).

Notes: \*

in this focal length.

Figure 8. Measurement of image co-ordinates of the fisheye lenses in Pictran D software (Left picture: taken from the combination of iPhone 4S camera with Olloclip 3 in one; right picture: taken from the combination of Nikon Coolpix8700 camera with Nikon FC-E9 fisheye lens).

The resulting image co-ordinates were evaluated in bundle block adjustment software developed by Dr. Danilo Schneider in Dresden Technical University in Germany. According to the bundle block adjustment results, Tables 2 and 3 were acquired.

The results of bundle block adjustment calculation by the software for 13 images captured with iPhone 4S camera and Olloclip 3 in one are given, respectively; the sigma0 value is 0.00099 and the pixel size is 0.0022 mm. The results of bundle block adjustment calculations by the software for 13 images captured with Nikon Coolpix8700 camera and FC-09 fisheye lens are given, respectively; the sigma0 value is 0.00163 and the pixel size is 0.0022 mm.


Table 2. Calibration results of two different fisheye in bundle adjustment software.


Table 3. Calibration parameters calculated for equidistant model.

Figure 9. Three-dimensional position of projection points with regard to antenna; three-dimensional co-ordinates of the camera as the result of balancing (left image shows values for iPhone 4S camera with Olloclip 3 in one; and right image shows values for Nikon Coolpix8700 camera with Nikon FC-E9 fisheye lens).

Sigma0 is the root mean square (rms) of measurements for image co-ordinates after bundle block adjustment. Table 2 shows the resulting values in both of the calibrations. According to software's post-adjustment outputs, additionally, projection point parameters (X0, Y0, Z0 and omega, phi, kappa) of the 13 images and object points' significance for both of the camera and lens combination are 8, which is 99.9%. (Software' significance values are 1: no significance, 2: 80%, 3: 90%, 4: 95%, 5: 98%, 6: 99%, 7: 99.8%, 8: 99.9% high significance) [87].

Figure 9 shows actual positions of three-dimensional co-ordinates of calibration field obtained by adjustment results and projection points of each of the 13 images that come from both of the calibration files acquired after adjustment.
