# Development of Height Indicators using Omnidirectional Images and Global Appearance Descriptors
## 4 Sets of Images  
Several complete sets of images captured both indoors and outdoors have been used to test the five methods proposed in the previous section. They have been captured by ourselves inside and in the surroundings of the Innova building at Miguel Hernandez University (Spain), and they are available from [48]. In this section, the main features of these sets of images are presented. The catadioptric vision sensor used consists of an Imaging Source DFK 21 BF04 color camera with 1280 \(\times\) 960 pixels resolution, and a hyperbolic mirror, whose model is Eizoh wide 70. Table 1 shows the main specifications of the mirror. Additional information on the mirror can be found in [49]. The camera has been adapted to a tripod that permits capturing images with a range of 165 cm along the \(z\)-axis of the WRS. Also, the mirror has been mounted above the camera, with their axes aligned. The distance between the focal points of the mirror and the camera is equal to 65 mm. Figure 11 shows the equipment used. The calibration of the camera has provided the following equation:  
\[f(a) =-212.5180+3.200\cdot 10^{-3}\cdot a-8.1262\cdot 10^{-6}\cdot a^{3}+\] \[+1.4931\cdot 10^{-8}\cdot a^{4}. \tag{15}\]  
As stated in Section 2, this function permits obtaining the coordinates of the retroprojection of each pixel of the image onto the hyperbolic mirror with respect to the CRS. \(a\) represents the distance in pixels between the pixel considered and the center of the omnidirectional image. To capture the sets of images, 21 positions have been defined on the ground plane indoors and outdoors. On each position a line parallel to the \(z\)-axis of the WRS has been considered and a set of images has been captured along each vertical line. Outdoors, 10 positions have been defined \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Mirror Eizoh Wide 70** \\ \hline Geometry & Hyperbolic \\ Maximum Diameter & 70 mm \\ Height & 35 mm \\ Angle of view above the horizon & 60 deg \\ Angle of view below the horizon & 60 deg \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of the mirror. Figure 11: (**a**) Hyperbolic mirror, (**b**) Color CCD Camera and (**c**) tripod. and 12 omnidirectional images per position have been captured, changing only the coordinate along the \(z\)-axis. This coordinate takes values between 125 cm and 290 cm with a gap of 15 cm between consecutive capture points. Indoors, 11 positions have been defined. The ceiling has limited the number of images captured from some positions. Table 2 shows the z-coordinate of each capture point and the number of images captured from each z-coordinate, considering both the outdoor and the indoor database. Figure 12 shows the position of the different ground positions above which each set of images has been captured. For each omnidirectional image, a cylindrical and an orthographic projection have been calculated with 256 \(\times\) 1024 and 256 \(\times\) 256 pixels each. About the choice of the capture positions, on the one hand, the outdoor images were captured both close to and far from buildings, in a parking area and gardens. Some sample omnidirectional images captured outdoors, from different positions, are shown in Figure 13. On the other hand, indoor \begin{table}
\begin{tabular}{c c c c} \hline \hline \(h\) & **z (cm)** & **\# Im. Outdoors** & **\# Im. Indoors** \\ \hline
**1** & 125 & 10 & 11 \\
**2** & 140 & 10 & 11 \\
**3** & 155 & 10 & 11 \\
**4** & 170 & 10 & 11 \\
**5** & 185 & 10 & 11 \\
**6** & 200 & 10 & 11 \\
**7** & 215 & 10 & 11 \\
**8** & 230 & 10 & 10 \\
**9** & 245 & 10 & 8 \\
**10** & 260 & 10 & 6 \\
**11** & 275 & 10 & 6 \\
**12** & 290 & 10 & 5 \\
**TOTAL \# IMAGES** & **120** & **112** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: \(z\)-coordinates of the capture points of the sets of images and number of images captured from each \(z\)-coordinate. Figure 12: Bird’s eye view of the positions above which each set of images was captured (**a**) outdoors and (**b**) indoors.