Download - Quality Control. of State-of-the-art Digital Elevation Data. Thomas Knudsen, Danish Geodata Agency
State of which art?
Admission:
This is really a case study using new Danish elevation data.
Brief detour: History of Danish elevation data.
History of Danish elevation data
1880-1910: Military surveyors, 2 m contours.
2007 - 2008: LiDAR, ½ point / m2
2014 - 2015: LiDAR, 4 points / m2
“Beauty contest”
Spring 2013: Tender - data for a new Danish elevation modelSelection criteria: Minimum requirements (“at least as good as 2007 data”), fixed maximum price (“at most xx MDKK”)Fall 2013: Contract awarded to a consortium led by AeroData Nederland
State of which art?
The art of being in the sweet spot between
1. Data density2. Data quality3. Price
Specification philosophy
1. Do not specify anything that cannot be checked
2. Check everything specified
What are we trying to achieve?
1. Make sure data delivered are up to specs2. Create metadata documenting just how good
data are3. Check consistency with other geodata
getting better impression of the accuracy of the entire geodata stack
2007 2014
Horizontal Precision ? < 15 cm
Accuracy 60 cm 15 cm
Vertical Precision 5 (8) cm 2 (5) cm
Accuracy < 15 cm 5 cm
How?
● Delivery in blocks < 40 km x 40 km● Blocks consist of up to 1600 1 km x 1 km
tiles● Most checks tile based● Trivially parallellizable
Horizontal accuracy
Comparison with hypothetical roof ridges derived from building outlines from the MapDB.
Point cloud roof reconstruction (3D Hough transform)
Roof ridge is the comparison target.
But they need some material to run with…
● Points classified as buildings outside building outlines
● Building outlines with no building points● Buildings on roads● Vegetation below buildings…
Implementation● Heavy lifting done by OSGeo et al. open
source products (GDAL, PostGIS, NumPy, SciPy, QGIS etc.)
● Tied together using internally developed code (also Open Source)
● LAStools (mostly the open source parts)● i.e. simple to scale: No licensing worries
Results
Very nice!
● Things work● Data quality is high● Supports a smooth communication with the
data provider● We work on releasing source code