# A Low-Cost Contactless Overhead Micrometer Surface Scanner
## 4 Results
### Conditions  
In all experiments, the sensor was operated in autofocus and automatic stacking mode. The illumination was produced by the sensor's flash and ambient light. Sensor brightness, contrast, and color balance were set to automatic. The utilized sensor provides images encoded in JPEG format, at 4000 \(\times\) 3000 p resolution. The average size of the image file is 2.4 Mb. The frequency of image reacquisitions, as per Section 2.4, was \(\approx\)1/1000. The effective scanning area is 33 \(\times\) 37 cm\({}^{2}\) and is a region of the printing bed at its center, allowing for laterally bounding paraphenalia. The maximum elevation of the C3 Dp was 30 cm. This elevation determines the height of a hypothetical pyramid. When the sensor is at that height, it occurs at its apex. In each layer of this pyramid, the lateral overlap is 50% for horizontal or vertical adjacency and 25% for diagonal. The pyramid has 5 layers, configured as in Table 3. Doubling the elevation per layer results in a medial overlap of \(\approx\)4, meaning that a parent node fully overlaps with 4 images from a finer layer. This level of medial overlap was sufficient for the samples we scanned. Denser or sparser configurations are treated in the same way. For the utilized sensor, the base layer of this pyramid is 5 \(\times\) 5 cm\({}^{2}\) and is covered by 25 \(\times\) 19 = 475 images. Figure 6: Samples. Figure 7: Sample details. The inequality between the numbers of X and Y steps is by preference. Given the rectangular camera FoV, this configuration results in a square scanned area. The surface region covered by each image is shown in the top row of Figure 8. Each image corresponds to a pyramid layer, ordered from left to right and from coarse to fine scale. The surface area covered by each image is outlined using different colors for neighboring images. In the example, the square formed in the rightmost map is 5 \(\times\) 5 cm\({}^{2}\). The bottom row shows the acquired images warped to the mosaic map or, in other words, the mosaics obtained for each pyramid layer. For the leftmost map, one image was warped; this image is the one acquired at the pyramid apex. The remainder maps are mosaics of warped images acquired at the locations denoted in the third and fourth column of Table 3. The rightmost mosaic comprises of 475 images. In the remainder of this section, the obtained mosaics are cropped to omit blank areas. The mosaics presented in Figures 9-13 image the same amount of area. The dimensions of the mosaics in Figures 14 and 15 are reported in Sections 4.2.5 and 4.2.7, respectively. The sensitivity of the keypoint detector was tuned to its highest level. The number of keypoint features detected in the original images typically ranges 30-60 K features per image. Datasets with more intricate texture, such as the banknote and textiles, exhibited about 100 K features per image. However, the robust correspondences across image pairs are much fewer and are in the range of 0.5-5 K. The reprojection error threshold employed to judge the reliability of a homography estimate was \(\tau=25\) p (see Section 3.2). The same computer was used in all experiments. Its specifications were as follows: CPU x64 Intel i7 8-core 3 GHz, RAM 64 Gb, GPU Nvidia GeForce GTX 4 Gb RAM (GTX1070), SSD 256 Gb, HDD 2 Tb. The critical parameter is RAM as it determines the number of correspondences that can be stored in memory and, ultimately, the number of images that can be stitched into a mosaic given the capacity of said memory. The use of time and computational resources, as a function of the scanned area, is reported in Table 4.  
Figure 8: Scanned area and mosaics per pyramid layer.