SPIE is working with SAE International to develop lidar measurement standards for active safety systems. This multi-year effort aims to develop standard tests to measure the performance of low-cost lidar sensors developed for autonomous vehicles or advanced driver assistance systems, commonly referred to as automotive lidars. SPIE is sponsoring three years of testing to support this goal. We discuss the second-year test results. In year two, we tested nine models of automotive grade lidars, using child-size targets at short ranges and larger targets at longer ranges. We also tested the effect of high reflectivity signs near the targets, laser safety, and atmospheric effects. We observed large point densities and noise dependencies for different types of automotive lidars based on their scanning patterns and fields of view. In addition to measuring point density at a given range, we have begun to evaluate the point density in the presence of measurement impediments, such as atmospheric absorption or scattering and highly reflective corner cubes. We saw dynamic range effects in which bright objects, such as road signs with corner cubes embedded in the paint, make it difficult to detect low-reflectivity targets that are close to the high-reflectivity target. Furthermore, preliminary testing showed that atmospheric extinction in a water-glycol fog chamber is comparable to natural fog conditions at ranges that are meaningful for automotive lidar, but additional characterization is required before determining general applicability. This testing also showed that laser propagation through water-glycol fog results in appreciable backscatter, which is often ignored in automotive lidar modeling. In year two, we have begun to measure the effect of impediments to measuring the 3D point cloud density; these measurements will be expanded in year three to include interference with other lidars.
This paper describes the initial results from the first of 3 years of planned testing aimed at developing methods, metrics, and targets necessary to develop standardized tests for these instruments. Here, we evaluate range error accuracy and precision for eight automotive grade lidars; a survey grade lidar is used as a reference. These lidars are tasked with detecting a static, child-sized, target at ranges between 5 and 200 m. Our target, calibrated to 10% reflectivity and Lambertian, is a unique feature of this test. We find that lidar range precision is in line with the values reported by each manufacturer. However, we find that maximum range and target detection can be negatively affected by presence of an adjacent strong reflector. Finally, we observe that design trade-offs made by each manufacturer lead to important performance differences that can be quantified by tests such as the ones proposed here. This paper also includes some lessons learned, planned improvements, and discussion of future iterations of this activity.
Target recognition and classification in a 3D point cloud is a non-trivial process due to the nature of the data collected from a sensor system. The signal can be corrupted by noise from the environment, electronic system, A/D converter, etc. Therefore, an adaptive system with a desired tolerance is required to perform classification and recognition optimally. The feature-based pattern recognition algorithm architecture as described below is particularly devised for solving a single-sensor classification non-parametrically. Feature set is extracted from an input point cloud, normalized, and classifier a neural network classifier. For instance, automatic target recognition in an urban area would require different feature sets from one in a dense foliage area.
The figure above (see manuscript) illustrates the architecture of the feature based adaptive signature extraction of 3D point cloud including LIDAR, RADAR, and electro-optical data. This network takes a 3D cluster and classifies it into a specific class. The algorithm is a supervised and adaptive classifier with two modes: the training mode and the performing mode. For the training mode, a number of novel patterns are selected from actual or artificial data. A particular 3D cluster is input to the network as shown above for the decision class output. The network consists of three sequential functional modules. The first module is for feature extraction that extracts the input cluster into a set of singular value features or feature vector. Then the feature vector is input into the feature normalization module to normalize and balance it before being fed to the neural net classifier for the classification. The neural net can be trained by actual or artificial novel data until each trained output reaches the declared output within the defined tolerance. In case new novel data is added after the neural net has been learned, the training is then resumed until the neural net has incrementally learned with the new novel data. The associative memory capability of the neural net enables the incremental learning. The back propagation algorithm or support vector machine can be utilized for the classification and recognition.
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