## 5 Experimental Results and Discussion
### Image Matching and Pattern Recognition  
The BRISK and ORB feature point descriptors along with the corresponding detectors proposed by the authors of these descriptors were evaluated in the ModAR prototype. Specifically, the AGAST detector combined with the BRISK descriptor and the FAST detector along with an orientation assignment mechanism combined with the ORB descriptor were used. Two different parameterizations were evaluated for each combination of detector-descriptor, as summarized in Tables 4 and 5. The difference in the experiments performed by the AGAST and BRIEF operators lies in the number of octaves. Specifically, 3 octaves were evaluated in the experiment \"AGAST-BRISK-3\", while 2 octaves were used in the experiment \"AGAST-BRISK-2\". The difference in the experiments performed by the oriented FAST detector and ORB descriptor lies in the maximum number of feature points per image, i.e., 2000 features for the experiment \"FAST-ORB-200\" and 500 features for the experiment \"FAST-ORB-500\". \begin{table}
\begin{tabular}{c c c} \hline \hline
**Experiment** & **AGAST-BRISK-3** & **AGAST-BRISK-2** \\ \hline AGAST detection threshold score & 30 & 30 \\ Number of octaves & 3 & 2 \\ Scale applied to the pattern used for & 1 & 1 \\ sampling the neighborhood of each feature & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameterization evaluated in the experiments performed using the AGAST detector and the BRISK descriptor. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Pattern Image** & **Dimensions (Pixels)** & **Resolution (MP)** \\ \hline BOTERO & \(348\times 717\) & 0.25 \\ SCYTHE & \(300\times 245\) & 0.07 \\ SURVEYING & \(310\times 450\) & 0.14 \\ JEFFERS & \(250\times 294\) & 0.07 \\ PAINTING & \(336\times 252\) & 0.08 \\ CRAFFITI & \(400\times 347\) & 0.14 \\ \hline
**3D Model** & **Size (KB)** & **Faces/Vertices** \\ \hline POTTERY & \(167\) & \(3296/1661\) \\ BUST & \(903\) & \(8767/4555\) \\ STATUE & \(1690\) & \(21/453/42/712\) \\ CHURCH & \(87\) & \(14,645,744/7,335,148\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dimensions and resolution of the pattern images as well as size and number of faces and vertices of the 3D models used in the experiments. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Experiment** & **FAST-ORB-2000** & **FAST-ORB-500** \\ \hline Maximum number of features & 2000 & 500 \\ Pyramid decimation ratio: ratio of each dimension (i.e., width/height) of the image of a pyramid level with its & 1.2 & 1.2 \\ corresponding dimension in the next pyramid level & & \\ Number of pyramid levels & 8 & 8 \\ Image border size where features are not detected (pixels) & 31 & 31 \\ The level of the pyramid of the source image & 0 & 0 \\ The number of points that forms each element of the & 2 & 2 \\ oriented BRIEF descriptor by comparing their brightnesses & & \\ Algorithm used to rank features & Harris & Harris \\ Size of the patch used by BRIEF (pixels) & 31 & 31 \\ FAST threshold & 20 & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Parameterization evaluated in the experiments performed using the oriented FAST detector and the ORB descriptor. The number of feature points extracted in each pattern image for every experiment performed by the ModAR prototype is outlined in Table 4. The experiment FAST-ORB-2000 yields the greatest number of feature points in each pattern image, which significantly differs based on the pattern image. The small dimensions of each pattern image along with the lack of corners in some of them resulted in much less features than the maximum threshold of 2000 in this experiment. The experiment FAST-ORB-500 yields approximately similar numbers of feature points in each pattern image (lying within the range of 400-500 features), because of the threshold of 500 features per image. The experiments AGAST-BRISK-3 and AGAST-BRISK-2 yield approximately the same number of features in the tests performed with the same pattern images, as their only difference is the number of octaves used in scale-space.