GEOL 452/552 - GIS for Geoscientists I

Lecture 23 - LiDAR

• LiDAR - some background (thanks to Chris Kahle, DNR)

• Where to get Iowa Lidar data

• Converting Lidar point data to a raster

• Visualization/Analysis (small subset, pre-made full tiles)

• Data in \follow along\lidar_ex (ames_lidar_data_ex.mxd)

• We’ll skip download and conversion to point shape file

• We’ll use a mini-data set as raw point data instead

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30 m DEM

Lidar:~ 1 point per square metervertical: 6 cm -15 cm

problems over water

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Scanning Lidar

elevation of about 5,000 feet shooting up to 150,000 pulses per second.Measures return time of each pulse to calculate the elevation of impact point

Uses hi-res GPS

Courtesy of Dodson & Associates

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Returns

!Multiple returns per pulse

!Waveform Returns

!Intensity

Slide courtesy of USGS

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USGS 2005 CSC-2 contract with Sanborn

! Productized LiDAR: FEMA, Standard, High-res

! FEMA and Standard Product Specs: "1.4 m postings

Accuracies"18.5 cm vertical RMS @ 95% confidence (~7.28 inches)"37 cm vertical RMS in vegetation (~14.57 inches)"1 m horizontal RMS @ 95% confidence (39.37 inches)

Bare Earth Product"Vegetation removed: FEMA product 95%; (90% - Standard product)"Artifacts removed: FEMA 90%; (89% - Standard) "Outliers removed: FEMA 95%; (90% - Standard)"Buildings removed: FEMA Product 98%; (95% - Standard)

! Deliverables: ASCII x,y,z,i text files; LAS all return binary files

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Lidar representations:

3D point cloudTIN (points connected to triangles)Raster (interpolated from 3D points)

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Lidar Bare Earth

Lidar Last Return

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Find and measure sinkholes under vegetation cover

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Mormon Trail remnants – Union County, Iowa

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Lidar - processing steps• Iowa: Need to download 2 km

x 2 km “tiles”

• Download tiles as .las format (binary) or .xyzi (text)

• Each tile: ~ 2 - 3 million points (!), size: 100 Mb (compressed), Shape file: 300 Mb

• Raw resolution: ~ 1 m (x/y)

• www.geotree.uni.edu/lidar/ (google geotree lidar)

• need to install 7zip (freeware zip) to uncompress .7z files

• (but don’t d/l & unzip now ...)

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• Rename .las file

• Convert .las file into (Multi) point shape file

• ArcTools: 3D Analyst - Conversion - From File - LAS to Multipoint

• (Remember to activate 3D analyst extension, even for ArcTools)

2 km x 2 km tile

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LAS File(s)

shape file

very small to get all points

For Iowa DNR data:Class Code filter needs to be 2 for bare earth (cleaned up data)!

Set to UTM15 NAD 83 (in Iowa)

ANY RETURNS

(No Input Attributes)

(tool takes 5-10 min per tile)

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• Creates Multipoint shape file

• Means: each feature contains many points

• Here 26k multipoints, 2.2 Mio points total (full tile)

• Includes elevations (Z) but no real attributes*

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• Your turn:

• let’s assume you’ve created a point shapefile from .las file

• Use: Skunk_river_subset (blue points)

• Bare Earth data

• Only 132k points instead of 2-3 mio.

• zoom in, measure point distance

• But: what’s the elevation?

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• Next step - make a raster from points

• (1 m bare-earth DEM)

• Use IDW interpolation

• (Spatial A. - Interpolate to raster)

• power = 2, Variable search radius

• BUT, number of points = 1

• elevation from closest point

• output cell size: 1 m

Symbolize DEM as stretched, with elevation color, Minimum-Maximum

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• Make hillshade (Spatial A. - Surface Analysis) of bare earth DEM (25 degr. Azimuth)

• Layer Properties - Display

• Switch on World Imagery layer

• make hillshade 30% transparent (contrast 20%)

• set to bilinear Interpolation (Resample)

• What happened to the bridge?

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more (optional)

• make a profile on bare earth (BE) DEM, figure out the grade of the railroad

• make a “DEM” and hillshade from first returns (FR) point layer (Skunk_river_first_returns)

• this will show the tree canopy, top of buildings

• How would you visualize the differences in elevation from bare earth to first returns?(same colormaps, Effects toolbar)

• How would you get the difference and volume of “stuff” between FR and BE?

• For the lazy:

• Look in “full tile” layer groups:

• has bare Earth and first return rasters (1 m res.)

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Rasters in ArcScene (optional)

• Open ArcScene - keep ArcMap open

• in ArcMap - copy (Right-click) the 1m DEM

• Paste into ArcScene: R-click on Scene layers - Paster Layer(s)

• Scene Layers - Properties: Set Vertical Exaggeration to 5 (background: black?)

• DEM layer - Properties:

• Rendering - Effects: Set Shade to ON and smooth to ON

• Display - Resample: Bilinear

• Base Heights - Height: Use DEM for heights, set to 1 m raster resolution

• Click Full extent (globe right of Hand)

• Scene layers - properties: Illumination: play with direction & azimuth (~ 10), high contrast

• (try to make a flyover movie)

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Wrap - up

• No more lectures, please work on class project

• I’ll be here TT 9-11 for help with projects!

• Go-around for 552: what’s your plan?

• (I have some potentially interesting data ...)

• All meet again here for Final exam Prep/Review session on Dec. 8 (Tues. Dead week)

• Material: textbook chapters 1 - 8, 12(13)

• Need review questions! Use WebCT - Discussions

• Dec. 10: All meet here for project presentations (10 slides, 10 min., powerpoint)

• Dec. 15: 9:30-11:30 Final “Live” part: Multiple Choice test (20 min.) + practical

• practical questions will be on WebCT Dec 14., WebCT hand in before Dec. 17 (midnight!)

• Poster version of class project (100 dpi, jpg, < 10 Mb) until Dec. 18

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