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

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.”

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 (an instrument that lets an operator see two photos at once in a stereo view). These photos are also used in automated processing for Digital Elevation Model (DEM) creation.

Close-range Photogrammetry the camera is close to the subject and is typically hand held or on a tripod. Usually this type of photogrammetry work is non-topographic - that is the output is not topographic products like terrain models or topographic maps, but instead drawings and 3d models. Everyday cameras are used to model buildings, engineering structures, vehicles, forensic and accident scenes, film sets, etc.

PROCESS FLOW

=> RAW DATA FORM CLIENT=> AERIAL TRIANGULATION=> DATA CAPTURING=> DEM GENARATION=> CONTOUR GENARATION=> ORTHOPHO GENARATION=> GIS CONVERSTION

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 (an instrument that lets an operator see two photos at once in a stereo view).

AERIALTRIANGULATION

Aeotriangulation adopts photogrammteric triangulation which establishes the geometric relationships among overlapping and sidelapping photographs to determine supplemental horizontal and vertical control points

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

Run #1

Run #2

Overlapping photography

Endlap - ~60%

Sidelap - ~20-30%

PLANIMETRIC FEATURE EXTRACTION

Buildings Transportation Features Hydro Features Utilities Vegetation Breaklines DTM points Bridges

PointPoint

LineLine

PolygonPolygon

VectorVector RasterRaster

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

Zone of cells

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PLANMETRIC FEATURES

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

In the most cases the term digital surface model represents the earth's

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

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

In the most cases the term digital surface model represents the earth's

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

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

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

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.

The constructed 3D model

3D BUILDING MODEL

Photogrammetry …. Lecture 11Dr. Steve Ramroop

ORTHO PHOTO GENARATION

ORTHO PHOTO GENARATION

Usually orthoimages do have some geometric limitations, they do show only the elements located in the height level of the used DEM in the correct location. Buildings not included in the DEM, are shifted with the location of the roofs depending upon the tangent of the nadir angle of the image location multiplied with the building height. So also parts of the facade can be seen If the height value of the roof is included in a detailed DEM, the roof is shown in the correct position corresponding to an orthogonal map projection. This is causing the problem that for some parts, before hidden by the roof, no information is available for the orthoimage

location of a building in a usualorthoimage based on a DEM the bare

including ground

orthoimage with the corrected location ofthe building roof

ORTHOIMAGE

ORTHOIMAGE

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

The output of photogrammetry is typically a map, drawing or a 3d model of some real-world object or scene. Many of the maps we use today are created with photogrammetry and photographs taken from aircraft.