NAND-measure: An Android App for Marker-based Spatial Measurement

In a disaster scenario, a quick decision must be made whether a bridge is stable enough to be used. The natural frequencies of a bridge can provide information about its condition. The actual frequencies (e.g. measured by the acceleration sensor built into a smartphone) must be compared with the desired frequencies. The desired frequencies can be approximated for example with the Finite Element Method (FEM).Among other parameters, the FEM requires the dimensions of the bridge. Numerous applications for spatial measurement for different purposes are offered in the mobile App-stores. However, most of these apps are limited to short distances of up to five meters and are not suitable for the aforementioned scenario. In this article, we present NAND-Measure - an application for spatial measurements for short distances (below one meter) up to distances of 50 meters. Two methods have been implemented - a stereoscopic approach with a single camera and an approach based on the pinhole camera model. Both methods were evaluated by taking sixty over different distances. Overall, the approach based on the pinhole camera model was more accurate and showed smaller deviations.