Post on 22-Dec-2015
Lidar and the Oregon Lidar Lidar and the Oregon Lidar ConsortiumConsortium
Portland State Office Building:
photo and lidar point cloud
Beaverton: photo and lidar highest hit model
Eagle Creek landslides, abandoned railroad: photo and
bare earth model
What is lidar (light detection and ranging)?What is lidar (light detection and ranging)?- Simply making lots of accurate distance - Simply making lots of accurate distance measurements with a laser rangefinder.measurements with a laser rangefinder.
Accurate laser rangefinders are commonly used as surveying instruments, measuring tapes, rifle scopes, even golf aids! Distance is calculated
by measuring the time that a laser pulse takes to travel to and from an object.
Millions of very precise laser range measurements are Millions of very precise laser range measurements are made made
from a precisely located aircraft, producing an accurate from a precisely located aircraft, producing an accurate and detailed 3-D map of the earth’s surface, as a “point and detailed 3-D map of the earth’s surface, as a “point
cloud.”cloud.”On-ground RTK-GPS base stations broadcast corrections to airborne GPS unit, locating the aircraft with an accuracy of a few centimeters.
Aircraft attitude is precisely measured by Inertial Motion Unit, so that the exact position and orientation of the laser rangefinder is always known.
The rangefinder scans across the surface at 100,000 to 200,000 pulses per second, collecting millions or billions of precise distance measurements, which are converted to 3-D coordinates.
Point cloud data define the 3-D shape and location
of the land, vegetation, and structures.
(above) Animated point cloud image of the Portland LDS Temple; points are colored by their relative height: red highest, blue lowest.
(right) Photo of the same building; note statue on left hand spire, visible in both images.
The complete collection of measured points for an area is called the point cloud, which is the fundamental form of lidar data. It provides a very detailed and accurate 3-D map of ground surface, vegetation, and structures.
Each laser pulse can produce multiple consecutive Each laser pulse can produce multiple consecutive measurements from reflections off several surfaces in its measurements from reflections off several surfaces in its
path.path.
• red= 1st return
• yellow = 2nd return
• green = 3rd return
This provides detailed images of vegetation structure and density, and returns data from the ground under tree cover.
Image on the left is a point cloud lidar view of the tree in the photo on the right. Each point is colored by which return it was from a particular pulse:
OLC data are collected at very high pulse density, OLC data are collected at very high pulse density, producing very detailed images.producing very detailed images.
Point cloud image on left compared to orthophoto on right shows actual point density of lidar data acquired over school bus lot. Each bus has been measured by 180-200 lidar points!
The lidar point cloud can even image livestock The lidar point cloud can even image livestock in the field!in the field!
Red and yellow clusters of points above ground are Red and yellow clusters of points above ground are cattle standing or lying in pasture.cattle standing or lying in pasture.
Very high point density means that even in heavily forested areas, it is Very high point density means that even in heavily forested areas, it is still possible to get a large number of measurements of the ground. still possible to get a large number of measurements of the ground. Left image is orthophoto of the Tualatin River, right image is lidar Left image is orthophoto of the Tualatin River, right image is lidar point cloud with point cloud with red points high, blue points low. red points high, blue points low.
The lidar vendor uses a variety of software filters to choose the points out of the point cloud that measure the ground surface. In the image on the right, vegetation points are green and ground points yellow. Even in thick forest there are numerous ground points.
Even if only one point in one hundred is a ground point, the huge number of points means that a smooth seamless ground model can be made. The image on the left is a bare earth digital elevation model, with 3 ft pixels, and reveals incredible detail of the terrain beneath the trees, including a hidden landslide.
For comparison, the best previously available ground model is shown on the left. The 10-m USGS Digital Elevation Model shows only a crude representation of the real surface.
Bare earth lidar can show features that Bare earth lidar can show features that you cannot even see on the ground.you cannot even see on the ground.
Perspective view of lidar (Dec. 2007) on left matches photograph
(July 2008) on right. The lidar was flown before clear cut logging of the reddish-brown slope, yet clearly shows an old logging road that is barely visible in the
photograph.
Arrows connect matching locations.
Lidar intensity image with 1 ft pixels
Additional standard lidar products include a “highest hit” Additional standard lidar products include a “highest hit” or “first returns” model, which shows the tops of trees or “first returns” model, which shows the tops of trees
and buildings, and buildings, and an intensity image, which is a form of infrared and an intensity image, which is a form of infrared
photograph.photograph.True color orthophoto with 0.5 ft pixels Lidar highest hit model with 3 ft pixels
Transmission lines
Nursery stock
Quarry
Residence
Auto
Lidar data allow a wide variety of information about Lidar data allow a wide variety of information about forests to be measured with unprecedented accuracy forests to be measured with unprecedented accuracy
and completeness.and completeness.
• Locate and measure individual trees in forest
• Estimate fuel loads, carbon content, timber volume
• Tell conifer from deciduous
• Identify damaged forest
Image at right shows a simple analysis, subtracting the bare earth surface model from a first return (highest hit) surface model to produce a canopy height model. Low canopy is violet, high is red. The shapes of individual trees are apparent, and the tallest tree in the forest can be easily found and measured.
Tallest tree at 252 ft!
Brush and grass
40-60 ft forest
50-80 ft forest
60-100 ft forest
100-125 ft forest
150-250 ft forest
135-190 ft forest
Comparing the highest hit or surface and bare earth surface Comparing the highest hit or surface and bare earth surface provides provides
a detailed and accurate model of building area and heighta detailed and accurate model of building area and height
Building, 9,000 sq ft, 27 ft high
Building, 4,900 sq ft, 11 ft high
Residence, 2,300 sq ft, 12 ft high
Building, 19,850 sq ft, 89 ft high
Building, 16,750 sq ft, 79 ft high
Light standards, 54 ft high
Building, 20,100 sq ft, 155 ft high
Overpass, 23 ft high
Highway sign, 27 ft high
Powerline, 56 ft high
Parking structure, 79,400 sq ft, 3-20 ft high, sloped for drainage
The highly detailed bare earth model allows for accurate location of The highly detailed bare earth model allows for accurate location of roads and provides easy access to unprecedented levels of detail about roads and provides easy access to unprecedented levels of detail about
slopes and shapesslopes and shapes Yellow lines are best current digital road map.
The lidar image can show where existing maps are inaccurate
or locate roads that are not on existing maps
or show where mapped roads do not exist
Because the bare earth model contains detailed information about the shape of the land surface, it is easy to construct a profile across a road to examine its construction and condition
Drainage ditch on uphill side
Roadcut not too steep
Properly crowned for drainage
Stream channels are readily apparent on lidar bare Stream channels are readily apparent on lidar bare earth imagesearth images
GIS software can automatically find stream channels from lidar data
Blue lines are streams generated by ArcGIS
Comparing the lidar-derived streams with the current digital stream map shows that the current data are often wildly inaccurate
Dark blue lines are best current digital stream map, light blue are lidar-derived.
misses sinuous channel, climbs ridges
Crosses divide, mouth wildly off
cross divides
In addition to accurately locating streams, lidar easily produces In addition to accurately locating streams, lidar easily produces accurate and detailed profiles and sectionsaccurate and detailed profiles and sections
Light blue line is lidar derived stream location, dark blue are section lines.
A detailed elevation profile down the stream shows areas of steep or gentle grade, waterfalls and pools. Culverts at road crossing show up as upward blips on the profile.
Stream section shows distinct floodplain and channel
Section shows “v” shape of rapidly downcutting stream
What can you do with lidar?What can you do with lidar?You can quickly, cheaply, and accurately….You can quickly, cheaply, and accurately….• Find landslides, old cuts and gradesFind landslides, old cuts and grades• Measure and estimate fills and cutsMeasure and estimate fills and cuts• Find stream channels, measure gradientsFind stream channels, measure gradients• Measure the size and height of buildings, bridgesMeasure the size and height of buildings, bridges• Locate and measure every tree in the forestLocate and measure every tree in the forest• Characterize land coverCharacterize land cover• Model floods, fire behaviorModel floods, fire behavior• Locate power lines and powerpolesLocate power lines and powerpoles• Find archeological sitesFind archeological sites• Map wetlands and impervious surfacesMap wetlands and impervious surfaces• Define watersheds and viewshedsDefine watersheds and viewsheds• Model insolation and shadingModel insolation and shading• Map road center and sidelinesMap road center and sidelines• Find law enforcement targetsFind law enforcement targets• Map landforms and soilsMap landforms and soils• Assess property remotelyAssess property remotely• Inventory carbon Inventory carbon • Monitor quarries, find abandoned minesMonitor quarries, find abandoned mines• Enhance any research that requires a detailed and accurate 2D or Enhance any research that requires a detailed and accurate 2D or
3-D map3-D map
With the USGS funds to anchor the survey and ensure a large enough area for the lowest possible rate, Federal, State and local government agencies added on their areas of interest until the entire project had grown to over 2300 square miles and $1.1 M, with over 20 funding partners.
The Portland Lidar Consortium was the The Portland Lidar Consortium was the first large scale effort to collect lidar in first large scale effort to collect lidar in
Oregon.Oregon.
In 2003, the USGS funded DOGAMI for a pilot lidar survey to look for earthquake faults.
This was followed in 2005 by another USGS-DOGAMI flight in the Portland Hills, a USGS survey of the Columbia River Floodplain, and a survey by Oregon City of its urban growth boundary.
In 2006, the USGS provided DOGAMI with $100k to complete the City of Portland. DOGAMI formed the Portland Lidar Consortium to develop funding partnerships to increase the area.
“Hood to Coast” survey
The Oregon Lidar Consortium (OLC) originated in 2007 with a The Oregon Lidar Consortium (OLC) originated in 2007 with a request by DOGAMI to the 2007 legislature for funds to request by DOGAMI to the 2007 legislature for funds to
acquire acquire lidar over the inhabited parts of Western Oregon.lidar over the inhabited parts of Western Oregon.
• The legislature provided $1.5 M of the 4.5 M request and encouraged DOGAMI to seek funding partners to increase coverage
• The relatively small amount of funding requires prioritization to areas with significant local contributions
Blue hatch at left shows the original $4.5 M target based on the inhabited area of Western Oregon.
Red hatch shows the area that could be covered by $1.5 M, magenta shows existing data.
DOGAMI Business Plan for the OLCDOGAMI Business Plan for the OLC
• Collection areas should be large and contiguousCollection areas should be large and contiguous• Collection areas initially anchored by significant contribution Collection areas initially anchored by significant contribution
from local funding partnerfrom local funding partner• OLC builds on anchor funding by finding additional partnersOLC builds on anchor funding by finding additional partners• State funds used to knit together partner areas State funds used to knit together partner areas • State funds are spent on the inhabited areas of the stateState funds are spent on the inhabited areas of the state• Collection areas completely outside the inhabited areas are Collection areas completely outside the inhabited areas are
fine if fully partner fundedfine if fully partner funded• Data in public domainData in public domain• Where possible, collection areas should include entire 6th field Where possible, collection areas should include entire 6th field
watershedswatersheds
DOGAMI selected a vendor to DOGAMI selected a vendor to provide lidar to the consortium.provide lidar to the consortium.
A nationwide RFP led to the selection for Watershed Sciences Inc. A nationwide RFP led to the selection for Watershed Sciences Inc. of Corvallis, Oregon, as the lidar vendor for the consortium under of Corvallis, Oregon, as the lidar vendor for the consortium under Oregon Price Agreement 8865.Oregon Price Agreement 8865.
OLC lidar prices are a function of area. DOGAMI adds OLC lidar prices are a function of area. DOGAMI adds 10% to the vendor price for quality control and 10% to the vendor price for quality control and
management.management.
Data SpecificationsData Specifications
• Laser spot size on ground 15-40 cm
1m
1m
• Aggregate pulse density > 8/m2
• 50% sidelap for complete double coverage
• Swath to swath consistency 15 cm (same point measured by adjacent swaths must have similar value)
• Absolute accuracy of each point
20 cm horizontal and vertical
Point cloud image of field and building: red points are from one swath, blue from another.
DOGAMI provides three-way independent quality control for DOGAMI provides three-way independent quality control for
OLC data.OLC data. 1. Compare accurately surveyed
control points to the final lidar product to test absolute accuracy (+/- 20 cm).
GPS elevation = 50.40 m
Lidar elevation = 50.38 m
Error = 2 cm
OLC lidar image showing DOGAMI quality control points (red triangles) collected by RTK-GPS survey.
2. Compare adjacent points from overlapping swaths to test consistency (+/- 15 cm)
Colors indicate data from different swaths
Swath to swath differences, measured on hundreds of thousands of points per swath, average about 3 cm in this example
Lidar production software is used to automatically compare locations for huge numbers of points from overlapping swaths.
3. Inspect bare earth models for artifacts, processing errors
“Bird” anomalies produce spikes in bare earth model
OLC Data ProductsOLC Data Products
Report and metadata !!Aircraft trajectories
3 ft pixel bare earth DEM ESRI format (quad tiles)
Ground points in LAS format (1/100 quad
tiles)
1 ft pixel intensity images (1/4 quad tiles)
Point cloud, LAS format 1/100 quad tiles
3 ft pixel first return DEM ESRI format (quad tiles)
Data Distribution OptionsData Distribution Options
• NOAA LDART website (point cloud)NOAA LDART website (point cloud)• USGS CLICK website (point cloud)USGS CLICK website (point cloud)• USGS NED website (DEM)USGS NED website (DEM)• GEO spatial data library website (DEM)GEO spatial data library website (DEM)• METRO (Portland area only)METRO (Portland area only)• PSLC (“Hood to Coast” area only)PSLC (“Hood to Coast” area only)• DOGAMI website (planned)DOGAMI website (planned)• DOGAMI publications on disk or drive (planned)DOGAMI publications on disk or drive (planned)
Copies are provided on external hard drives as soon as DOGAMI completes QC.
Funding partners:
Public:
As of September 2008, 25 partners As of September 2008, 25 partners have added $2.7 million to the Oregon have added $2.7 million to the Oregon
Legislature’s $1.5 million.Legislature’s $1.5 million.
The City of Philomath
The City of Turner
As of September 2008, the OLC has been successful in As of September 2008, the OLC has been successful in building partnerships for several lidar collections around building partnerships for several lidar collections around
the state.the state.Current status at Current status at http://www.oregongeology.com/sub/projects/olc/default.htm