Lidar Quality Checks via FME Workbenches

Geospatial Data ServicesManitoba Hydro

Geospatial Data Services

Support Manitoba Hydro’s operational activities … through the application of spatial data processing and reporting tools.

About Us

Technical Assistant Technical Assistant Rock Star(Geomatics Engineer)

John Huillery Justin Avery Arch Csupak

Lidar Data Acquisition:GDS is responsible for coordinating the lidar requirements of the Corporation.-Includes Lidar and DOI for new and existing transmission corridors and wide area mapping

Data Volume:Over the last few years we have contracted the data collection for 3000 km of corridor studies and 1000 sq. km of wide area mapping.This translates to about 5 TB of data which we have to perform QC and acceptance testing on.

QC and Acceptance:We have fairly detailed specifications for many deliverables with specific criteria including formats, projections, and legacy vertical datums.

Therefore we needed a way to automate the process.

Lidar Quality ChecksAmongst several other checks, FME is used to:-Perform initial checks for classification errors.-Determine how new lidar data compares vertically to previous lidar missions.

Initial Classification Checks

LAS Format 1.4 Specified for 2015 Lidar Collection

Allows for extended classification scheme

LAS 1.4 format includes the use of classification flags:

• Key Point (thinned data for modeling purposes)• Overlap (adjacent flight lines)

• Synthetic (points added after collection)• Withheld (points that contain errors)

Class Flags are supplied as codes 0 to 15, and can consist of combinations of multiple class flags.

How do Key Points Help?

Can now be identified/treated as rock outcrop, paved road, etc. within a given

analysis or model.

Classification flags also introduce the possibility of error.

FME is used to identify initial class / classification flag errors.

Workbench Part 1Due to LAS file sizes and memory limits, 1 tile is processed at a time through a Workspace Runner transformer.

Workbench Part 1‘Prompt and Run’

One Input LAS Folder Location

One Output File LAS file summaries and errors

Pressing ‘OK’ starts second workbench as a sub-routine, which processes each tile in turn.

Workbench Part 2LAS Checks:• Determine Horiz.+Vert. Coord. System and LAS version

• Test for illegal class/class flag combinations (ie. Key Point in vegetation, Key Point and Withheld flag existing on same point, etc.)

• Summarize findings in MS Excel Workbook:• One sheet for error summary• One sheet summarizes LAS version, Horz / Vert Coord. System• One sheet per tile (contains detailed summary of all points)

Workbench Part 2

Results

Results

Results

Class 13 = Wire - Guard

Vertical Datum Validation

• Validate vertical datum with respect to previous datasets

Vertical Datum Validation

• Validate vertical datum with respect to previous datasets• Verify data conforms to specifications

Vertical Datum Validation

• Validate vertical datum with respect to previous datasets• Verify data conforms to specifications• Easily identify elevation anomalies

Workflow - Vertical Datum Validation

Workflow - Vertical Datum Validation

FME

Identify Intersecting LiDAR Coverage

Known Vertical Datum

Unknown Vertical Datum

Z-Delta Calculator Workbench

Z-Delta Calculator WorkbenchCreate point grid of AOI(s)

Generate TIN from LiDAR (both)

Extract elevation values to point grids and calculate difference

Calculate Statistics

AOI Summary Stats

Results Excel Workbook

Results Feature Class

Create Point Grid of Area(s) of Interest

Generate TINs from LiDAR

Extract z-Delta Values to Point Grid

Extract z-Delta Values to Point Grid

Calculate Descriptive Statistics

Thank you!