If you can't read please download the document
Upload
deborah-arnold
View
217
Download
0
Embed Size (px)
DESCRIPTION
Overview What is LIDAR? What is SGM? Key Differences Accuracy Comparison SGM Examples Popular SGM Applications
Citation preview
SGM as an Affordable Alternative to LiDAR
February 2016 by Frank Wilson of ControlCam, LLC Overview What is
LIDAR? What is SGM? Key Differences
Accuracy Comparison SGM Examples Popular SGM Applications What is
LiDAR? LIDAR, which stands for Light Detection and Ranging, is a
remote sensing method that uses light in the form of a pulsed laser
to measure ranges (variable distances) to the Earth. Travel time of
light pulses can be used to create a three-dimensional
representation of the surface Can penetrate low density objects
including trees The data generated forms a point cloud and is
output into a .LAS format What is SGM? Semi-Global Matching (SGM)
is a robust stereo method that is derived from aerial images and
can be used to extract three dimensional dense point clouds of a
surface SGM data derived from this process creates a point cloud
dataset comparable to LiDAR It can be exported into a .LAS format
to be utilized by third party software similar to LiDAR data Key
Differences SGM LiDAR
~ 172 points per Square Meter at 3 GSD SGM Semi-Global Matching
(SGM) can be based on high resolution imagery and each pixel can be
processed to render a 3-D Point Cloud of high density (150 to 380
points per square meter) Up to 9 points per Square Meter LiDAR
LiDAR derived point clouds are limited by the sampling frequency of
the sweeping beam and the laser beam width (1 to 9 points per
square meter) Key Differences (contd.)
A LiDAR derived 3-D Model is lower resolution and thus lacks
sufficient resolution to see surface changes that Semi-Global
Matching (SGM) detects However, current SGM software renders
surfaces that have more low level noise than LiDAR surfaces LiDAR
Derived SGM Derived Images from the paper SEMI-GLOBAL MATCHING: AN
ALTERNATIVE TO LIDAR FOR DSM GENERATION? By S. Gehrke, et al, Key
Differences (contd.)
BothLiDARandSGMmethodsresultinhighdensitydigital
surfaces,whichtypicallyrequireadditionalprocessingoreditingbeforetheycanbeusedinanapplication.
SGM is typically 15 to 30 times more dense than LiDAR Both can have
data classified automatically to determine bare earth, buildings or
vegetation content with minor changes to classification rules
ThehigherdensityoftheSGMDSMscaneaseidentificationof structures in
the data, making manual editing less error prone LiDAR data
canbecapturedregardlessoflightconditions(evenatnight) and the laser
pulses can penetrate into a forest canopy to measure the ground
directly With SGM color can be accurately co-registered in the 3D
point cloud and oblique imagery can be used to reconstruct building
facades Table 1. Comparison between LiDAR and SGM
Accuracy Comparisons Due to a combination of sensing methods and
geometry, LiDAR has a greater accuracy in height than in horizontal
position For high precision work typically 5 cm in Z and 10 to 30
cm in XY LiDAR point accuracy can also be affected by atmospheric
conditions (such as mist or volcanic ash) or by target reflectance
LiDAR SGM Horizontal Accuracy 10-30 cm (altitude-dep.) 0.5 GSD
Vertical Accuracy 5 cm 1.5 GSD Typical High Resolution 30 cm
Surface Measured top and ground top Processing time 1,000,000
Points/s 10,000-20,000 points/s Table 1. Comparison between LiDAR
and SGM SGM accuracies are driven by the triangulation accuracies
of the imagery, which is typically 0.5 GSD horizontally and 1.5 GSD
vertically The resulting pixel level correlation generated point
cloud is photogrammetrically accurate to the same level as the
mapping A USGS Accuracy Assessment of LiDAR found that it had a
mean accuracy of 30 cm and variability of cm and cm Units in
meters.Table from the USGS Accuracy Assessment of the U.S.
Geological Survey National Elevation Dataset By Dean B. Gesch, et
al, SGM Example SGM of Mayport NAS in Jacksonville, FL
Not an image, but rather a 2.5 dimensional model of the NAS
rendered from Nadir Stereo Pairs 2nd SGM Example SGM of Port of
Palm Beach FL
Also a 2.5-D model, but rendered from both Nadir Stereo Pairs and
Oblique Imagery to reduce noise and fill in object sides 3rd SGM
Example Winterhaven, FL
Also a 2.5-D model, but rendered from both Nadir Stereo Pairs and
Oblique Imagery to reduce noise and fill in object sides SGM
Applications SGM can be a more cost effect method to do traditional
applications of LiDAR including: Local County Government tax
assessing departments usage for cost effectively generating
building footprints for tax purposes and then perform YoY change
detection Detection of progress/changes in the Construction or
Mining industry Utility Industry can use Imagery and SGM to detect
changes to Right of Ways and assess alternative routes
Transportation departments can use SGM for highway and corridor
mapping Commercial industry can use SGM combined with aerial
imagery for a host of business opportunities Questions