Abstract
Terrestrial laser scanning is a promising technique for automatic measurements of tree stems. The objectives of the study were (1) to develop and validate a new method for the detection, classification and measurements of tree stems and canopies using the Hough transformation and the RANSAC algorithm and (2) assess the influence of distance to the scanner on the measurement accuracy. Tree detection and stem diameter estimates were validated for 16 circular plots with 20 m radius. The three dominating tree species were Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and birch (Betula spp.). The proportion of detected trees decreased as the distance to the scanner increased and followed the trend of decreasing visible area. Within 10 m from the scanner, the proportion of detected trees was 87% on average for the plots and the diameter at breast height was estimated with a relative root-mean-square-error (RMSE) of 14%. The most accurate diameter measurements were obtained for pine, which had a RMSE of 7% for all the full 20 m radius plots. The RANSAC algorithm reduced noise and made it possible to obtain reliable estimates.
Highlights
Advanced models are currently being used to support sustainable management of forest resources with consideration to several values such as timber production, pulpwood, biodiversity, and bioenergy, for example in the forest management planning system Heureka [1]
A terrestrial laser scanning (TLS) system measures the distance to surrounding objects with mm-resolution based on the emission of laser light and the detection of reflected signals
The modified Random Sample Consensus (RANSAC) algorithm validated in this study has the potential to produce reliable estimates based on laser returns that are from both tree stem and branches
Summary
Advanced models are currently being used to support sustainable management of forest resources with consideration to several values such as timber production, pulpwood, biodiversity, and bioenergy, for example in the forest management planning system Heureka [1]. There are at least two limitations of the current manual field inventory methods used for retrieving tree data: (1) only a small portion of all trees are measured on sample plots; and (2) there are no detailed measurements of individual trees. The most promising technology for automated measurements of tree stems is terrestrial laser scanning (TLS). Such systems are rapidly becoming less expensive and more compact while at the same time the measurement frequency is increasing, allowing for very detailed measurements of a field plot within a few minutes. A TLS system measures the distance to surrounding objects with mm-resolution based on the emission of laser light and the detection of reflected signals. There are two common approaches when scanning a field plot: single scan and multiple scan
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