Adelaide 2013 LiDAR classification and derived products  

Authors / CoAuthors

Abstract

This document details the methods and results of the project Adelaide LiDAR Classification and Derived Products¿ performed by RPS for Geoscience Australia in 2013. Lineage and Accuracy Statements for ANZLIC metadata documents for each of the project deliverables are included. Airborne LiDAR data was acquired over Adelaide in September 2008 and North Adelaide in September 2011. Differences in the level of classification reduced the ability to integrate the data into an accurate, seamless and consistent coastal DEM suitable for detailed modelling the potential impacts of coastal inundation or riverine flooding. The objective of this project was to reclassify both the 2008 and 2011 point clouds to ICSM Level 3 and derive hydro flattened 1m bare earth DEMs and; 0.25m cartographic contours, all inline with the ICSM LiDAR Acquisition Specifications. Figure 1. Adelaide LiDAR Reclassification 2012 overview map The LiDAR The LiDAR was provided as tiled LAS files. RPS did not apply any vertical or horizontal adjustments to the LiDAR and is unable to comment on the spatial accuracy of the point cloud. The deliverables were: Classified ICSM Level 2 and Level 3 point clouds in LAS format 1 metre DEMs in ESRI Binary grid format 0.25 metre contours in ESRI Shape format Break lines in ESRI Shape format. This report All files were named according to the ICSM file naming specifications.

Product Type

dataset

eCat Id

100484

Contact for the resource

Keywords

Australian and New Zealand Standard Research Classification: Fields of Research

• Earth Sciences

( {1} )

• HVC_144648

( {1} )

• Elevation

( {1} )

• Lidar

( {1} )

• Published_Internal

Publication Date

2018-04-19T01:38:21

Creation Date

2014-08-01T00:00:00

Security Constraints

Australian Government Security ClassificationSystem    

Classification - unclassified

Legal Constraints

Creative Commons Attribution 4.0 International Licence    

Access - license

Use - license

Status

Purpose

The objective of this project was to reclassify both the 2008 and 2011 point clouds to ICSM Level 3 and derive hydro flattened 1m bare earth DEMs and; 0.25m cartographic contours, all inline with the ICSM LiDAR Acquisition Specifications.

Maintenance Information

asNeeded

Topic Category

geoscientificInformation

Series Information

Lineage

Metadata Statements Classified Level 3 LiDAR Point Data Lineage The supplied LiDAR was upgraded to Level 3 by manual reclassification of the LIDAR points in profile and plan view, to ensure that only actual ground points are assigned to class 2. The two datasets provided had been classified to different schemes. 1. The ¿2008 Adelaide¿ dataset was classified to ground (2), model key points (8) and other (10). Initially, model key points were reassigned to ground and other were reassigned to unclassified (1). 2. The ¿2011 North Adelaide¿ dataset was classified consistent with the ICSM specification. Vegetation points (3, 4 & 5) were reassigned to unclassified. Overlap points and buildings were unchanged. This is the most efficient starting condition for manual improvement as it is only necessary to reallocate points between two classes (ground and unclassified) to improve the ground classification from level 2 to level 3. Manual reclassification of the ground surface was applied by systematic visual scanning of the point cloud in profile view at large scale in TerraScan software also using a plan view of the relief shaded terrain surface as reference. Above ground points misclassified as ground (spikes) were reassigned to unclassified. Similarly ground points that have not been correctly classified were assigned to the ground class. During this process, water (9) was reclassified from ground or unclassified by tracing water boundaries. These boundaries were saved as break lines for hydro flattening. Bridges (10) were classified in profile. After the ground classification had been ungraded to Level 3, unclassified points were automatically reclassified to low vegetation (3), medium vegetation (4) and high vegetation (5). Model Key points were automatically generated as a subset of the ground points. For North Adelaide, building points were automatically classified. No manual effort was employed to improve the accuracy of the above ground classes except bridges. These classes are not considered reliable (for example, powerlines are likely to be included in high vegetation and there is some misclassification between buildings and high vegetation). The reclassified LAS tiles were visually rescanned at 25% of the initial scale in a quality assurance check and corrected as necessary. Quality Statement The workflow and quality assurance processes were designed to achieve the Level 3 requirement ¿to ensure that only actual ground points are assigned to class 2¿ and achieve a ground point misclassification rate of 1% or less. The classification accuracy was not measured. 1m Digital Elevation Model (DEM): Lineage A 1m DEM has been generated from the LiDAR ground points. The method of deriving the height for each grid point is by triangulation between the three nearest LiDAR ground points. Hydro flattening was applied using waterlines (break lines) that were manually digitised using the LiDAR and ortho photography as reference for areas of non-tidal water greater than 625 square metres and watercourses nominally greater than 30 metres in width. The DEM was exported to ESRI Binary grid as 1km by 1km tiles in accordance with ICSM specifications (in December 2012). Quality Statement The DEM accuracy will be limited by the spatial accuracy of the LiDAR point data and will contain some additional error due to interpolation, particularly in areas of dense vegetation where ground points are sparse. The may also be a small amount of error due to ground point misclassification. Contours: Lineage Contours were generated in the TNTmips geospatial software using a bilinear interpolation method. The contours have an interval of 0.25m. Contours are traced across a moving window of user specified size. The larger the window size the smoother the resulting contours. A window of 7x7 DEM pixels was used to generate the contours.

Parent Information

Extents

[-35.059707, -34.555871, 138.335469, 138.743886]

Reference System

GDA94 / MGA zone 54 (EPSG:28354)

Spatial Resolution

1 Metre

Service Information

Associations

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