Mobile LiDAR scanning and 3D slope scanning for the geotechnical engineering service is one of the major applications for MMS (Mobile mapping system). LiDAR (light detection and ranging) slope scanning can help engineers and surveyors to retrieve the terrain back from the on-ground measurement to office point cloud post-processing. Unlike the photogrammetry-based slope scanning approaches, the LiDAR scanning setup is more accurate than the photogrammetric meshing model for slope or regional terrain reconstruction. LiDAR can obtain both vertical and horizontal control by measuring the distance of the reflected light from sensors, unlike photorealistic meshing only maintain horizontal control but is weak in vertical terrain reconstruction.

• Introduction and market identification
• Methodologies for the Mobile LiDAR system

Concept of Handheld LiDAR in slope scanning application

LiDAR point cloud capturing from mobile device (this figure demonstrate the Apple iPhone 12 Pro)

Handheld LiDAR is a relatively new technology that has the potential to revolutionize many industries. It is a type of remote sensing technology that uses pulsed light and lasers to measure distances and capture accurate 3D images of surfaces. This is done by sending out millions of laser pulses and measuring the time it takes for them to return.

Handheld LiDAR can be used for a variety of purposes, including mapping, surveying, navigation, and 3D scanning. It can also be used to detect changes in the environment and make better decisions. For example, it can be used to detect changes in soil composition, vegetation, and water levels.

This new sensor uses a laser light to measure the distance between points and create 3D models of the environment. The LiDAR sensor works by measuring the time it takes for the laser light to travel from the sensor to an object and back. It then uses this data to create a 3D map of the object or environment. The sensor then uses the distance of the object from the sensor to create an accurate 3D model.

Depth map generation and digital photogrammetry from mobile device (this figure demonstrate the Apple iPhone 12 Pro)

The depth map generation process in digital photogrammetry involves the following steps:

1. Image acquisition: The first step involves taking multiple photographs of a scene from different angles to capture as much visual information as possible.
2. Image alignment: The next step is to align the images in order to register the points in the photos and create a 3D model. This is done using image registration methods such as the iterative closest point (ICP) algorithm.
3. Feature extraction: Features such as edges and corners are extracted from the images and used to create a point cloud.
4. Surface reconstruction: Surface reconstruction algorithms are used to generate a 3D surface model from the point cloud.
5. Depth map generation: Finally, the depth map is generated by projecting the 3D surface model onto the photos. This is done by computing the distances between each point in the 3D model and the corresponding point in the photo.

Concept of SfM (Structure from Motion) using Lai King road slope as sample

Digital photogrammetry employs the use of Structure from Motion (SfM) to analyze photographs to create accurate 3-dimensional models. SfM works by examining many overlapping photos taken from different angles and using them to create a 3D point cloud. This point cloud is then used to generate a 3D mesh that accurately reflects the shape of the object being photographed.

The SfM process begins by taking photos of the object from different angles, orientations, and distances. It is important to take many photos from different views, as this will greatly improve the accuracy of the 3D model. The photos are then uploaded to a photogrammetric software, which then uses the data from each photo to build the 3D model.