Amanda Lind from Blue Marble Geographics discusses an automated technique for extracting curbs as line features from elevation data utilizing Global Mapper.
This article delves into two distinct approaches for extracting curbs as line features from elevation data using Global Mapper. The primary focus is on the automated method that leverages the Breakline tool, which identifies line features where the curb alters the slope from a flat roadway. The alternative method involves a manual extraction process using the Path Profile tool to position line vertices along the curb.Both techniques yield line features that include elevation attributes.
The Breakline tool evaluates elevation grids to identify breaklines, illustrated here in red. If starting with lidar data, ensure that ground points are classified and a Digital Terrain model (DTM) grid is generated from these points to achieve a smoother surface.
Global Mapper offers automated extraction capabilities for various features such as buildings, trees, cables, and power poles from lidar data. But how can curbs be effectively extracted? If you possess elevation data and need to delineate the curb’s edge, the Breakline tool is your solution. Breaklines function similarly to contour lines; though, rather of marking elevation changes, they indicate shifts in slope. Curbs represent these slope changes in or else flat regions. With the right configurations, the Breakline tool can serve as an efficient curb extraction mechanism.
configuring Breakline Settings
The Breakline tool includes three extraction methods, but the emphasis here is on the final option: Find Breaklines at Any surface Break. In the Breakline Setup dialog,select the “Profile” curvature grid type to generate lines that align with the curb’s slope. The Edge Threshold settings inform Global Mapper about the steepness of the slope you wish to extract. adjust the Detect Threshold slider significantly to the right to concentrate on the nearly vertical cliffs typical of curbs. The Connect Threshold should be slightly lower than this value to prevent the erroneous connection of separate curbs. It’s crucial that the Edge Detect Threshold is equal to or greater than the Edge Connect threshold.
Settings applied for the terrestrial lidar grid.
Struggling to generate breaklines in your dataset? Consider creating a Curvature Grid to visualize and test your breakline settings. The Breakline tool utilizes a curvature grid derived from your data to produce breaklines. This curvature grid can also assist in troubleshooting by allowing you to visualize cell size and extraction methods. For instance, create a 1-meter grid followed by a 0.1-meter grid and compare the results. The objective is to clearly identify curbs in the black-and-white grid. If the features appear indistinguishable, resembling TV static, adjustments to the settings are necessary. Additionally, ensure that the resolution of your elevation grid is sufficiently high to capture curb details.
These images illustrate the differences between 0.1m (effective) and 1m (ineffective) profile curvature grids. A higher resolution is essential for accurately detecting smooth curb features.
Are you generating an excessive number of line features? Ensure that the Minimum Break Length value is set high enough to eliminate lines shorter than your smallest curb. Increasing the Edge Detect Threshold can also help filter out breaklines that highlight the crest of the curve frequently enough found along the centerline of roads. Breaklines can be created along either the top or base of the curb, depending on the terrain’s curvature. For users requiring precise line features (greater than 6 inches), the manual extraction method may be more suitable.
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