Abstract
Abstract. When a target lies on discontinuous surfaces, the footprint of a laser rangefinder covering multiple ranges causes mixed pixels effect and significantly distorts the ranging quality. Meanwhile, the ranging error of incidence angle effect is triggered by a deformed footprint containing various ranges as well. Based on the commonality of causing ranging errors within one footprint, this study proposed an approach to tackle “generalized mixed pixels effect” correcting ranging errors involving in deformed footprint cases. Errors caused by generalized mixed pixels effect vary in rangefinders and are difficult to be uniformly treated. A correction model was formulated through integrating individual effects by considering the physical and geometrical aspects of laser ranging. An adjustment procedure was followed to estimate the parameters of the correction equation taking all observation uncertainties into account. To analyze the individual effects and eventually combine them into a complete model, a five-case workflow has been developed. Firstly, a divergence angle estimation method was presented to eliminate the mixed pixels effect by a decentering approach. Incidence angle effect was modeled and parameter was estimated by adjustment techniques. Particularly, since incidence angles are usually unknown in field surveys, an iterative estimation procedure was designed to obtain the optimal incidence angle of target points. Finally, offset correction accounting for generalized mixed pixels effect was formulated. Through the experimental tests on Trimble M3 DR 2” and Topcon GPT-3002LN, it is confirmed that the proposed method effectively resolves the ranging errors and preserves the ranging quality under generalized mixed pixels effect.
Highlights
A pulsed time-of-flight laser ranging technique with centering and horizontalization has been widely applied to acquire highquality ranges of interest
As long as a split-up footprint is shorter than the range resolution, the shortest distance a ranging instrument can distinguish between two target points, mixed pixels effect will still exist and distort ranging quality
This study presented a laser ranging correction workflow, aiming to correct ranging errors under generalized mixed pixels effect without any physical waveform information
Summary
A pulsed time-of-flight laser ranging technique with centering and horizontalization has been widely applied to acquire highquality ranges of interest. With only one laser pulse return, mixed pixels effect deceives the rangefinder with the footprint just involving one target. Based on Lambertian scattering law, the incidence angle effect, with a Corrections of generalized mixed pixels effect are different among rangefinders since signal processing algorithms are varied. It is difficult, if not impossible, to assess the ranging quality in a general form. Most of the rangefinders do not reveal the waveform information for general users to explore the intensityrange relationship (Adams, Probert, 1996) This means that even though intensity is the key to estimating the generalized mixed pixels effect, the intensity data should be seen as unknown
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