G.CHANDRA SEKHAR REDDY M.Tech(GIS)NIIT UNIVERSITY

PHOTOGRAMMETRY

VERY PRECISE 3D REPRESENTATION TIME EFFECTIVE COST EFFECTIVE BASED ON WELL ESTABLISHED AND

TESTED ALGORITHMS LESS MANUAL EFFORT MORE GEOGRAPHIC FIDELITY

WHY PHOTOGRAMMETRY

Photos – light Gramma – to draw Metron – to measure

“Photogrammetry is the technique of measuring objects from photographs”

“The art, science and technology of obtaining reliable spatial information about physical objects and the environment through the processes of recording, measuring and interpreting image data”

WHAT IS PHOTOGRAMMETRY?

Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure

Close-range Photogrammetry the camera is close to the subject and is typically hand held or on a tripod

Types of Photogrammetry

PROCESS FLOW

RAW DATA FORM CLIENT (SCANS) AERIAL TRIANGULATION DATA CAPTURING DEM GENARATION CONTOUR GENARATION ORTHOPHOTO GENARATION

In Aerial Photogrammetry the camera is mounted in an aircraft and is usually pointed vertically towards the ground

Multiple overlapping photos of the ground are taken as the aircraft flies along a flight path

These photos are processed in a stereo-plotter

AERIALTRIANGULATION

STEREO PHOTOGRAPHY

Adjacent but overlapping aerial photos are called stereo-pairs and are needed to determine parallax and stereo/3D viewing

AERIALTRIANGULATION

Overlapping photography

Endlap - ~60%

Sidelap - ~20-30%

OVERLAPPING STEREO PHOTOGRAPHY

RASTER AND VECTOR DATA

THE DATA PREPARATION

PLANMETRIC FEATURES

DATA OUTPUT

PLANEMETEIC FEATURE EXTRACTION

RASTER AND VECTOR DATA

Point

Line

Polygon

Vector Raster

Raster data are described by a cell grid, one value per cell

Zone of cells

Buildings Transportation Features Hydro Features Utilities Vegetation Breaklines DTM points Bridges

THE DATA PREPARATION

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PLANEMETEIC FEATURES

DATA OUTPUT

Stereo Image Vector Data

WHAT IS DTM AND DEM?

There is no common usage of the terms digital elevation model (DEM), digital terrain model (DTM) and digital surface model (DSM) in scientific literature

The digital terrain model represents the bare ground surface

The term Digital Elevation Model is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface

DEM GENARATION

Contour lines are lines drawn on a map connecting points of equal elevation

Contour lines are useful because they allow us to show the shape of the land surface (topography) on a map

This vertical spacing is referred to as the contour interval

If the contour interval is 10 ft. Each the contour lines was a multiple of 10 ft.( i.e. 0, 10, 20, 30)

In areas with high relief the contour interval is usually larger

CONTOUR LINES

CONTOUR LINES

DATA FOR THE 3D CITY MODELS

The 3D city models contain data, which is related to the Spatial objects

Those objects are generally topography, buildings, transportation, plant cover, infrastructure and other details related to the goal of application

3D city models are focused on buildings however it may contain roads, green cover, trees etc. according to the usage of model

A. Complete out boundary of a buildingB. The boundary and 3D rooftop segments

The constructed 3D model

3D BUILDING MODEL

Photogrammetry …. Lecture 11Dr. Steve Ramroop

3D CITY MODELING

ORTHO PHOTO GENERATION

ORTHO PHOTO GENERATION

Ortophotos are photographs that have been corrected for distortions

 Distortions from the camera lens, and relief

To use these orthophoto images as a map, it is of great importance to provide orthophoto

images in high level of accuracy

ORTHOIMAGE

ORTHOIMAGE

location of bridges uncorrected and corrected forheight differences against the road below

3D Representation and Visualization of real world is only possible with photogrammetry.The output of photogrammetry is typically a map Many of the maps we use today are created with photogrammetry and photographs taken from aircraft.

conclusion

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