Handling Large Lidar Datasets: Tips And Best Practices

Understanding LiDAR Data Complexity

LiDAR (Light Detection and Ranging) data is known for its massive file sizes that require specialized software to process and analyze. The complex point cloud structure contains dense XYZ coordinates that create an intricate 3D model of the scanned landscape.

Massive File Sizes Requiring Specialized Software

A single LiDAR data capture can produce billions of point measurements, with file sizes quickly growing into terabytes of data. The scale of information contained in raw LiDAR data exceeds the capabilities of traditional software. Managing and working with LiDAR datasets requires high-performance software designed specifically for manipulating vast clouds of 3D data points.

Complex Point Cloud Structure

LiDAR data is captured as a large collection of georeferenced point measurements, typically from aircraft equipped with scanning laser rangefinders. Each point contains precise 3D coordinates (XYZ) with attributes like intensity, number of returns, classification, etc. Structuring and organizing these massive crowds of intricate data points poses unique challenges for information storage, processing power, and visualization software.

Table of Contents

Strategies for Efficient Storage

The management of LiDAR data poses special requirements for information storage and retrieval solutions that can handle immense file sizes while optimizing data access and queries. Advanced data storage techniques like tiling schemes and cloud computing provide pathways for more effective organization.

Tiling Schemes for Spatial Indexing

Due to dense point clouds spanning large geographic areas, LiDAR datasets leverage spatial “tiling” to divide data into smaller sections that can be individually indexed. This allows efficient querying and extraction of data tiles from massive overall file sizes. Popular tiling schemes used with LiDAR include quadtree spatial indexing that recursively subdivides area into four quadrants.

Cloud-Based Storage Solutions

The scale of LiDAR data makes cloud storage a key strategy for providing flexible and scalable capacity for housing datasets. Cloud platforms offer distributed storage across servers along with computing resources to handle processing. This enables collaborative workflows for managing LiDAR data production, updates, access permissions and sharing.

Streamlining Data Processing

Processing techniques tailored for LiDAR provide vital pathways for transforming raw point clouds into usable information products. Optimizing datasets for 3D modeling along with leveraging GPU and distributed computing power allows users to focus on critical analysis tasks.

Tools for Point Cloud Optimization

Specialized tools for “cleaning” and optimizing point cloud data for 3D modeling include automatic point classification as well as filtering to remove outliers. This refinement of point measurements improves LiDAR alignment and creates optimal “bare-earth” terrain models. Such processing diminishes “noise” within data prior to surface generation and modelling.

Leveraging GPU and Distributed Computing

LiDAR data analysis leverages higher computing performance from modern GPUs along with distributed computing for “out-of-core” big data capabilities. This facilitates manipulation of massive point clouds exceeding a workstation’s RAM. Scaling up via HPC servers or cloud computing resources allows users to efficiently handle terabytes worth of LiDAR data that is increasingly collected and combined across projects.

Visualizing Results Effectively

Advanced 3D visualization techniques provide new perspectives for exploring and gaining insights from processed LiDAR results. Transforming raw point clouds into 3D model abstractions like digital elevation models enables results communication. Stylized rendering also exposes patterns within data representations.

Creating Digital Elevation Models

A core pathway for analyzing LiDAR data involves developing digital surface models that interpolate measurements into continuous elevation maps distinguishing bare earth, structures and vegetation. Bare-earth DEMs enable terrain analysis while surface models incorporating vegetation and buildings serve planning/engineering uses.

Stylized Rendering for Pattern Recognition

Enhanced rendering styles including contours, slopes, aspects, hillshading etc. expose patterns within LiDAR digital elevation models, often combined with aerial rasters. Such 2D map overlays and 3D surface visualization allows professionals to conduct geographic pattern analysis for tasks ranging from precision agriculture to disaster risk assessment.

Example Code for Handling Big LiDAR Data in Python

Modern scientific programming languages like Python offer a range of libraries tailored for LiDAR data manipulation. Example workflows utilizing PDAL and LasPy demonstrate typical processes for loading, filtering and analyzing large 3D point cloud datasets.

Python Libraries for Manipulating LiDAR (PDAL, LasPy)

PDAL provides extensive LiDAR data handling capabilities for tasks ranging from importing common formats like LAS to exporting derivative products such as DEMs. LasPy enables direct reading and writing of compressed LAS files along with key point cloud modifications. Such libraries build Python workflows around industry standard LiDAR data foundations.

Example Loading, Filtering, Analyzing Code

Here is sample Python code utilizing PDAL for pipeline chaining of common LiDAR processing steps:


import pdal
import numpy as np 

# Define PDAL Pipeline 
pl = pdal.Pipeline()  

# Read Entire LAS File
pl.readers.las.filename='large_lidar.las'

# Filter Points by Classification Value  
pl.filters.range(limits='Classification![7:17]')  

# Convert to Raster Digital Elevation Model        
pl.writers.gdal(...aigrid, output_type='min', resolution=1)

Similarly, LasPy enables direct parsing and manipulation of LiDAR data files:


import laspy

# Read LAS file
inFile = laspy.file.File("./sample.las")  

# Filter points based on scan angle
inFile.points = inFile.points[inFile.scan_angle < 15]

# Export subset to new LAS file
outFile = laspy.file.File("./sample_filtered.las", mode="w", header=inFile.header) 
outFile.points = inFile.points[:10**7]
outFile.close()

Together these examples demonstrate common handling, filtering and exporting of large LiDAR assets using Python for streamlined workflows tailored to big 3D point cloud data.