TOPOGRAPHIC LIDAR TOPOGRAPHIC LIDAR ACQUISITIONACQUISITION

TTI Production

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.

LIDAR ACQUISITION (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

TTI Production

LIDAR TECHNOLOGY AND DEM / DTM PRODUCTS

Sample of Digital Models with vegetation (left) and without vegetation (right)

Topographic productsContours at various intervals

Slopes

TINs

Rasters at various resolution

Points xyz

TTI Production

CONTACT :

David LOY

X 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

TTI Production

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.

TTI Production

LIDAR DEM AND DTM EXTRACTION

DIGITAL ELEVATION MODEL( DEM )

orDIGITAL TERRAIN MODEL

( DTM )

Lidar first pulse

Lidar first pulse

Interpolation

DEM

DTM (with buildings)

Real DTM interpolated

DEM (first pulse)

DTM (last pulse)

+

+ +

+

TTI Production

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 :

TOPOGRAPHIC 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

COTONOU AIRBORNE ACQUISITION PROJECT - 2014

Aerial optical images at 10 cm resolution were acquired at the same time that Lidar data TTI Production

Sample of aerial image at 10 cm resolution in panchromatic mode

COTONOU AIRBORNE ACQUISITION PROJECT - 2014

TTI Production

LIDAR Product : DEM = overall Elevation + Vegetation + Houses + other objects (cars, people, etc.)

In meters

COTONOU AIRBORNE ACQUISITION PROJECT - 2014 TTI Production

COTONOU AIRBORNE ACQUISITION PROJECT - 2014

LIDAR Product : DTM = Ground Elevation + interpolated elevation under objects (houses, cars, peoples, etc.)

TTI Production

COTONOU AIRBORNE ACQUISITION PROJECT - 2014

LIDAR Product : Objects Elevation = All objects (trees, houses, cars, peoples, etc.) (without ground elevation)

TTI Production

COTONOU AIRBORNE ACQUISITION PROJET - 2014

LIDAR Product : Housing Elevation (without ground, other objects and vegetation)

TTI Production

COTONOU AIRBORNE ACQUISITION PROJET - 2014

LIDAR Product : Housing Height = Houses elevation – (Interpolated ground elevation)

TTI Production

COTONOU AIRBORNE ACQUISITION PROJET - 2014

LIDAR Product : Vegetation Height = Vegetation elevation – (Interpolated ground elevation)

TTI Production

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Anaglyph

Stereo anaglyph lidar image – TTI Production

Stereo anaglyph lidar image – TTI Production

Anaglyph