Transcript Slide 1

Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Tutorial 2– Visualization of Lidar DEM Data
1. Load and color DEMs
2. Hillshade DEMs
3. Slopeshade DEMs
4. Combine shade and color
5. Differencing, canopy and serial data
6. Generating Contours
7. Point and Profile queries
8. Ground Point Density
Oct. 17-18, 2009
DOGAMI lidar data sample from
Carpenterville on Southern Oregon
Coast. Bare earth and highest hit (or
first return, or reflective surface) 3 ft
DEMs, from 8 pulse/m2 leaf on data.
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Load and color
DEM
Tutorial 2– Visualization of Lidar DEM Data
• Add data>
Bare_Earth_DEM and
Highest_hit_DEM
• Native scheme is
grayscale with low
values dark
• Right click layer>
properties> symbology
• Select your preferred
color scheme
• Note differences
between the two DEMs
• DEM image alone is not
a particularly useful
visualization
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Tutorial 2– Visualization of Lidar DEM Data
Hillshade
visualization
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Arc Toolbox> 3D Analyst>
Raster Surface> Hillshade
Input, Bare_Earth_DEM, set
output to be_hs_315.img,
accept defaults and run
Input Bare_Earth_DEM, set
output to be_hs_225.img,
set azimuth to 225 and run
Note difference in
hillshades, some
illumination angles simply
don’t work.
Experiment with
highest_hit_DEM, Azimuth,
Altitude, Z factor, shadows
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Tutorial 2– Visualization of Lidar DEM Data
Slopeshade Visualization
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Arc Toolbox> 3D analyst> Raster
surface> slope
Input Bare_earth_DEM, set output to
be_slope.img, run
Default color scheme is poison-dart
frog
Right click layer> properties>
symbology> choose stretched, invert,
standard deviations and set n to 5
Slopeshade map is “universal
hillshade”.
Shading curve can be adjusted to
illuminate features in the very steep
or very gentle ends of the slope
range, under Symbology, click
histograms and play with nodes on
curve to reshape
Experiment with Highest_hit_DEM
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Combine
layers
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Tutorial 2– Visualization of Lidar DEM Data
Turn off all layers
Load orthoimage
Right click layer> properties>
display> set transparency to 50%
Turn on highest hit hillshade or
slopeshade
Turn off all layers except beslope
and Bare_Earth_DEM. Drag
beslope below Bare_Earth_DEM,
set Bare_Earth_DEM display to 50%
transparency. This combination is
very useful for mapping geologic and
geomorphic features
Play with combinations of layers!
70 % orthoimage over 70% highest
hit hillshade over bare earth
slopeshade makes a nice basemap.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Differencing;
Canopy Height
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Tutorial 2– Visualization of Lidar DEM Data
Turn off all layers
Load Highest_Hit_DEM and
Bare_Earth_DEM
Arc Toolbox> 3D Analyst> Raster
Math> Minus
Use Highest_Hit_DEM for input 1,
Bare_Earth_DEM for input 2,
canopy.img for output, run
Right click canopy layer>
properties> display> set
transparency to 50% then
symbology and choose your
favorite color scheme
Turn on highest hit hillshade or
slopeshade and position under
canopy.
Combined image shows the height
of vegetation, structures, can you
find the transmission lines?
Note negative values in canopy.
Highest hit and bare earth surfaces
are made from different collections
of points.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Differencing;
Serial Data
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Tutorial 2– Visualization of Lidar DEM Data
Turn off all layers
Load be_leaf_off and be_leaf_on, select
one and click zoom to layer
Arc Toolbox> 3D Analyst> Raster Math>
Minus
Use be_leaf_off for input 1, be_leaf_on
for input 2, serial.img for output, run
Right click serial layer> properties>
display> set transparency to 50% then
symbology> classified, say yes to create
histogram, click on classify, and set
values to -3, -1, 1 and 3. Click ok to
return to main symbology tab, double
click patches to select color, set lowest
purple, next blue, next (-1 to 1) to “no
color” next to orange, highest to red.
Load leaf_off_beslope and place it under
serial
Image now shows areas of erosion as
orange and red, deposition as blue and
purple. You should be able to find two
landslides and three debris flow scars.
Widespread noise is due to differences in
ground models under heavy vegetation
Serial comparisons require high quality
data.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Contours
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Tutorial 2– Visualization of Lidar DEM Data
Arc Toolbox> 3D Analyst> Raster
Surface> Contour
Input be_leaf_off.img, accept default
output, set contour interval to 1, run.
Resultant 1m contours provide
additional detail on shape of
landscape, particularly in areas of low
slope.
Contours can greatly slow down
redraw, minimize this by using contour
with barriers and selecting a 1km grid
file as the barrier.
Contours from lidar can be very rough,
reflecting the high resolution of the
DEM and the natural roughness of the
surface. For nicer looking contours
without significant loss of accuracy, use
Arc Toolbox> Spatial Analyst>
Neighborhood> Focal Statistics to
smooth DEM before contouring.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Query Lidar,
Point and profile
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Tutorial 2– Visualization of Lidar DEM Data
Turn off all layers
Turn on slope_be and canopy, select
one and click zoom to layer
Click on info tool, select all visible layers,
click on point of interest to see point
location and elevation values
From main menu select View>
Toolbars> and check 3D Analyst
In 3D Analyst toolbar, click layer list
control and select canopy
From 3D Analyst toolbar select
interpolate line, draw line across area of
interest.
Initial interpolate line will be slow while
grid is indexed.
When line appears, select create profile
graph from 3D Analyst toolbar
Profile will appear in window, which can
be stretched in X or Y.
Right click profile to see print and export
options.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Ground Point
Density
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Tutorial 2– Visualization of Lidar DEM Data
It is important to understand how good
the data behind your DEM is, and ground
point density is critical
Add the file 42124B3317.GPD, right click
the layer and select zoom to layer
This is a vendor-supplied ground point
density grid, white areas have > 1 ground
point per 4m2, black areas less.
Zoom to a large area of black, and then
turn off the GPD grid, leave on only the
be_slope grid, note the obvious TIN
triangle outlines in the grid. This is a
simple graphic indicator of ground point
density. Use the measurement tool to
measure some of the TIN side lengths,
some are quite long.
To make your own groundpoint density
grid Arc Toolbox> Conversion> From
File> LAS to Multipoint, choose
44124B3317_ground as input,
ground_points as output, point spacing of
2 and run.
Select Arc Toolbox> Conversion Tools>
To Raster > Point to Raster, use
ground_points as input, pointcount as
value field, accept default output, set cell
assignment type to COUNT, cellsize to 15
and run.
Assign a color scheme to the resulting
raster, make it 50% transparent and
drape over the be_slope layer. Examine
how the DEM looks in areas of low point
density.
Oct. 17-18, 2009
Introduction to the Acquisition, Visualization and Interpretation of lidar-derived Digital Elevation Models.
Tutorial 2– Visualization of Lidar DEM Data
Additional Resources
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http://blogs.esri.com/Dev/blogs/geoprocessing/archive/2008/11/06/Lidar-Solutions-inArcGIS_5F00_part-1_3A00_-Assessing-Lidar-Coverage-and-Sample-Density.aspx
http://cws.unavco.org:8080/cws/learn/uscs/2008/2008Lidar/handouts/GeoEarthScopeDataTutorial
April08.pdf
<http://cws.unavco.org:8080/cws/learn/uscs/2008/2008Lidar/handouts/GeoEarthScopeDataTutori
alApril08.pdf>
http://cws.unavco.org:8080/cws/learn/uscs/2008/2008Lidar/handouts/GLW_and_ArcMap.pdf
<http://cws.unavco.org:8080/cws/learn/uscs/2008/2008Lidar/handouts/GLW_and_ArcMap.pdf>
http://arrowsmith410-598.asu.edu/Lectures/Lecture14/ <http://arrowsmith410598.asu.edu/Lectures/Lecture14/>
http://arrowsmith410-598.asu.edu/Lectures/Lecture15/ <http://arrowsmith410598.asu.edu/Lectures/Lecture15/>
Oct. 17-18, 2009