Lidar technology uses laser pulses to measure distances to the ground and other surfaces. When the pulses return, the time of flight is used to calculate distances and generate precise 3D maps. Lidar data can be processed to classify points and extract terrain models ignoring vegetation and buildings. This allows generating high-resolution digital terrain models and other products for applications like urban planning and flood modeling. The document describes a 2014 lidar and image acquisition project over Cotonou, Benin where calibration points were surveyed and various terrain products were created from processing the lidar data.

1. TOPOGRAPHIC LIDARTOPOGRAPHIC LIDAR
ACQUISITIONACQUISITION
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2. A characteristic of Lidar data is the separability of laser
beam. When the laser beam hits an object it is reflected
back to the mirror and the time interval between the pulse
leaving the airborne platform and the reflected signal is
measured.
The multiple backscattered beams on ground and through
some objects (trees, pylons, etc.) are recorded and
separated by return time order.
The data is post-processed and the LIDAR time-interval
measures are converted to distance and corrected using
the aircraft's onboard GPS receiver, IMU, and ground-
based GPS stations.
ISITION (LIght Detection and Ranging)
LIDAR technology collects a set of 3D points on
the Earth’s surface. The system emits toward a
target a series of light pulses with a known time
interval. Using an averaging process once again
a time over distance calculation is able to
measure the time of flight between the
transmitted and received sensors resulting in an
accurate speed and range measurement.
The LiDAR technology collects a huge
amount of data and a single survey can
easily collect millions of x,y,z points on huge
areas with an accuracy between 5 and 20
cm.
Some applications :
Planimetric and slope mapping
Trees or houses height analysis
Images ortho-rectification
Terrain analysis3-D modeling
Floodplain mapping and planning
Disaster management
Coastal erosion
Forestry
Land use mapping and planning
Volumetric studies - 3-D modeling
Electrical lines / pipes corridor mapping
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3. HNOLOGY AND DEM / DTM PRODUCTS
Sample of Digital Models with vegetation (left) and without vegetation (right)
Topographic products
Contours at various intervals
Slopes
TINs
Rasters at various resolution
Points xyz
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CONTACT :
David LOY

4. Y Z POINTS CLASSIFICATION
A dedicated software for Lidar data
processing, classifies xyz points to
separate housing or any man-made
structures from vegetation using
information on the first and last pulses.
Then, filters are applied to separate real
ground values and housings.
Filtered points to obtain the class
«vegetation»
Filtered points to obtain the class
«housing»
Each point (brown) is an
X,Y,Z measure of LiDAR
acquisition that means at
least 3 pts / m²
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5. By using only ground points, we can
construct a partial Digital Terrain Model.
We need to extract housing and structures,
then interpolate topography within the
“holes” to retrieve a complete and real
Digital Terrain Model.
LIDAR DATA PROCESSING
With Lidar data, it is
possible to produce
vector layers with
vertical attributes to
built accurate 3D
models.
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6. AR DEM AND DTM EXTRACTION
DIGITAL ELEVATION MODEL
( DEM )
or
DIGITAL TERRAIN MODEL
( DTM )
Lidar first pulse
Lidar first pulse
Interpolation
DEM
DTM (with buildings)
Real DTM interpolated
DEM (first pulse)
DTM (last pulse)
+
+ +
+
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7. APPLICATION: URBAN PROJECT – COTONOU (BENIN)
In 2014, TTI production & IMAO have completed a
LiDAR acquisition campaign over the city of
Cotonou to produce DTM and DEM for flooding
modelling and hydraulic analysis.
LiDAR and aerial image acquisition planning – 90 Km²
CONTACT :

8. IC MISSION TO CALIBRATE LIDAR DATA
TTI Production has done topographic mission to calibrate
LiDAR and optical images acquisition.
The post-processing requires reference points with DGPS
measurements to obtain an accuracy of ~ 10 cm.
Several targets made of large crosses (to be identified on
aerial images) have been painted on the ground in open
areas.
DGPS measurements using
ground targets to calibrate
the airborne mission
DGPS base device installation
for the duration of the mission
Position of calibration points

9. RBORNE ACQUISITION PROJECT - 2014
Aerial optical images at 10 cm resolution were acquired at the same time that Lidar data TTI Production

10. Sample of aerial image at 10 cm resolution in panchromatic mode
RBORNE ACQUISITION PROJECT - 2014
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11. LIDAR Product : DEM = overall Elevation + Vegetation + Houses + other objects (cars, people, etc.)
In meters
RBORNE ACQUISITION PROJECT - 2014 TTI Production

12. RBORNE ACQUISITION PROJECT - 2014
LIDAR Product : DTM = Ground Elevation + interpolated elevation under objects (houses, cars, peoples, etc.)
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13. RBORNE ACQUISITION PROJECT - 2014
LIDAR Product : Objects Elevation = All objects (trees, houses, cars, peoples, etc.) (without ground elevation)
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14. IRBORNE ACQUISITION PROJET - 2014
LIDAR Product : Housing Elevation (without ground, other objects and vegetation)
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15. IRBORNE ACQUISITION PROJET - 2014
LIDAR Product : Housing Height = Houses elevation – (Interpolated ground elevation)
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16. COTONOU AIRBORNE ACQUISITION PROJET - 2014
LIDAR Product : Vegetation Height = Vegetation elevation – (Interpolated ground elevation)
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17. Stereo anaglyph lidar image – TTI Production
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18. Stereo anaglyph lidar image – TTI Production
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19. Stereo anaglyph lidar image – TTI Production
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20. Stereo anaglyph lidar image – TTI Production
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21. Stereo anaglyph lidar image – TTI Production
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22. Stereo anaglyph lidar image – TTI Production

23. Stereo anaglyph lidar image – TTI Production

24. Stereo anaglyph lidar image – TTI Production
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