PhotogrammetryPhotogrammetryCE 426CE 426

IntroductionIntroduction

►Definition of Photogrammetry:Definition of Photogrammetry: the art, the art, science, and technology of obtaining science, and technology of obtaining information about physical objects and the information about physical objects and the environment by photographic and environment by photographic and electromagnetic images.electromagnetic images.

Basic InformationBasic Information

►Mapping from aerial photos is the best Mapping from aerial photos is the best mapping procedure yet developed for most mapping procedure yet developed for most large projects.large projects. Used successfully for maps varying in scale Used successfully for maps varying in scale

from 1:1,000,000 1:120 with contour intervals from 1:1,000,000 1:120 with contour intervals as small as 1 foot.as small as 1 foot.

Topographic mapping is the most common Topographic mapping is the most common form. – U.S.G.S updated and done this way.form. – U.S.G.S updated and done this way.

Used to reconstruct a scaled 3-dimensional Used to reconstruct a scaled 3-dimensional optical model of the lands surface using a optical model of the lands surface using a stereoplotterstereoplotter..

Basic InformationBasic Information►Uses: Aerial photosUses: Aerial photos

Aid: geological investigations, soil surveys, land Aid: geological investigations, soil surveys, land surveys, tax mapping, reconnaissance and surveys, tax mapping, reconnaissance and military intelligence, urban and regional military intelligence, urban and regional development, transportation system development, transportation system investigations, quantity estimates, shore investigations, quantity estimates, shore erosion, etc.erosion, etc.

Mathematical methods have been developed to Mathematical methods have been developed to make precise 3-dimensional measurements make precise 3-dimensional measurements from photos.from photos.

►Phototriangulation: 3-dimensional positioning of Phototriangulation: 3-dimensional positioning of survey stations.survey stations.

Basic Information ContinuedBasic Information Continued

Photo has been used to take geometric Photo has been used to take geometric measurements of human bodies, artificial measurements of human bodies, artificial human hearts, large radio telescopes, ships, human hearts, large radio telescopes, ships, dams, buildings and very accurate dams, buildings and very accurate reproductions.reproductions.

► In general it is not economical for small In general it is not economical for small projects – the cost break even point is projects – the cost break even point is somewhere between 30 – 100 acres somewhere between 30 – 100 acres depending on the situation.depending on the situation.

Basic InformationBasic Information

►Photogrammetry can not be used Photogrammetry can not be used successfully over the following types of successfully over the following types of terrain.terrain. Desert or plains areas, sandy beaches, and Desert or plains areas, sandy beaches, and

snow – the photograph as uniform shades with snow – the photograph as uniform shades with little texture.little texture.

Deep canyons or high buildings that conceal Deep canyons or high buildings that conceal ground surface.ground surface.

Areas covered by dense forest.Areas covered by dense forest.

2 Basic Categories 2 Basic Categories

►Metrical photogrammetry – obtaining Metrical photogrammetry – obtaining measurements from photos from which measurements from photos from which ground positions, elevations, distances, ground positions, elevations, distances, areas, and volumes can be computed and areas, and volumes can be computed and topographic or planimetric maps can be topographic or planimetric maps can be made.made.

►Photo interpretation – evaluation of existing Photo interpretation – evaluation of existing features in a qualitative manner.features in a qualitative manner.

Types of PhotogrammetryTypes of Photogrammetry

►Aerial – series of photographs of an area of Aerial – series of photographs of an area of terrain in sequence using a precision terrain in sequence using a precision camera.camera.

►Terrestrial – photos taken from a fixed and Terrestrial – photos taken from a fixed and usually known position on or near the usually known position on or near the ground with the camera axis horizontal or ground with the camera axis horizontal or nearly so.nearly so.

►Close range – camera close to object being Close range – camera close to object being observed. Most often used when direct observed. Most often used when direct measurement is impractical.measurement is impractical.

HistoryHistory

► The first use of photogrammetry was by Arago, a The first use of photogrammetry was by Arago, a French geodesist, in 1840. This included French geodesist, in 1840. This included topographic and terrestrial.topographic and terrestrial.

► The first aerial photogrammetry was by the French The first aerial photogrammetry was by the French in 1849 using kites and balloons.in 1849 using kites and balloons.

► Laussedat (French) – father of photogrammetry.Laussedat (French) – father of photogrammetry.► 11stst in N. America – Deville, Surveyor General of in N. America – Deville, Surveyor General of

Canada.Canada.► U.S.G.S. adopted photogrammetry as mapping U.S.G.S. adopted photogrammetry as mapping

process in 1894 – mapping border between process in 1894 – mapping border between Canada and Alaska.Canada and Alaska.

History History ►Airplanes brought great change to Airplanes brought great change to

photogrammetry.photogrammetry. 11stst used in 1913. used in 1913. Used extensively in WWI – photo interpretation.Used extensively in WWI – photo interpretation. Used in WWII – mapping for recon and Used in WWII – mapping for recon and

intelligence.intelligence.►WWII – 1960 – used often, expensive and WWII – 1960 – used often, expensive and

accuracy problems for engineering design.accuracy problems for engineering design.►After mid 60’s – advent of computer and After mid 60’s – advent of computer and

plotting has made photogrammetric plotting has made photogrammetric mapping accurate and affordable.mapping accurate and affordable.

Photogrammetry for EngineeringPhotogrammetry for Engineering

►Defined: Photogrammetry is the process of Defined: Photogrammetry is the process of measuring images on a photograph.measuring images on a photograph.

►Modern photogrammetry also uses radar Modern photogrammetry also uses radar imaging, radiant electromagnetic energy imaging, radiant electromagnetic energy detection and x-ray imaging – called detection and x-ray imaging – called remote remote sensingsensing..

Basic Categories of Basic Categories of Photogrammetric InterpretationPhotogrammetric Interpretation

►Metrical Photogrammetry – obtaining Metrical Photogrammetry – obtaining measurements from photos from which measurements from photos from which ground positions, elevations, distances, ground positions, elevations, distances, areas and volumes can be computed and areas and volumes can be computed and topographic or planimetric maps can be topographic or planimetric maps can be made.made.

►Photo interpretation – evaluation of existing Photo interpretation – evaluation of existing features in a qualitative manner – timber features in a qualitative manner – timber stands, water pollution, soils, geological stands, water pollution, soils, geological formations, crops, and military formations, crops, and military interpretation.interpretation.

Geometry of PhotographsGeometry of Photographs

►Orthographic projection – each point Orthographic projection – each point projected normal to reference plane.projected normal to reference plane.

►Perspective projection – each point Perspective projection – each point projected through a central point, due to projected through a central point, due to points being at different elevations, they points being at different elevations, they look 3 dimensional.look 3 dimensional.

►Principal point (center of photo) – located at Principal point (center of photo) – located at the intersection of lines joining the the intersection of lines joining the Fiducial Fiducial points.points.

►To perform computations, one must know:To perform computations, one must know: H = height above datum from which photos H = height above datum from which photos

taken.taken. f = focal length of camera lens – either in f = focal length of camera lens – either in

in or mm.in or mm.

► Items on photo:Items on photo: Fiducial pointsFiducial points DateDate Roll and Photo #Roll and Photo #

Scale of a Vertical PhotoScale of a Vertical Photo

► S = orS = or

► f = focal length 6” or 152.4 mm is commonf = focal length 6” or 152.4 mm is common► H’ = height of plane above groundH’ = height of plane above ground► h = height (elevation) of groundh = height (elevation) of ground► H = height of place above datum [altimeter H = height of place above datum [altimeter

reading (2% error)] reading (2% error)]

ffHH’’

ffH-H-hh

Scale of a Vertical PhotoScale of a Vertical Photo► Datum Scale = the scale which would be effective Datum Scale = the scale which would be effective

over entire photo if all points were projected over entire photo if all points were projected downward to datum.downward to datum.SSD D ==

► Average Scale = for photo planningAverage Scale = for photo planningSSAV.AV. = =

Average elevation can be determined for USGS Average elevation can be determined for USGS topo maps, etc.topo maps, etc.

ffHH

ffH-hH-hav.av.

Relief DisplacementRelief Displacement

► Relief Displacement exists because photos are a Relief Displacement exists because photos are a perspective projection.perspective projection.

► Use this to determine the height of object:Use this to determine the height of object:h=h=

h = height of objecth = height of objectd = radial distance to top of object-radial distance to d = radial distance to top of object-radial distance to

bottom of object.bottom of object.r = radial distance to top of object.r = radial distance to top of object.

d (H’)d (H’) rr

Planning and Executing Photo ProjectPlanning and Executing Photo Project

► Basic Overall Process:Basic Overall Process:1.1. Photography – obtain suitable photos.Photography – obtain suitable photos.2.2. Control – obtain sufficient control through field Control – obtain sufficient control through field

surveys and/or extension by photographic surveys and/or extension by photographic methods.methods.

3.3. Map Compilation – plotting of planimetric and/or Map Compilation – plotting of planimetric and/or topographic features.topographic features.

4.4. Map Completion – map editing and special field Map Completion – map editing and special field surveys.surveys.

5.5. Final Map Drafting Final Map Drafting

Elements of PlanningElements of Planning1.1. Conversion of requirements to project Conversion of requirements to project

specs.specs. Factors:Factors:1.1. Purpose of photogrammetryPurpose of photogrammetry

a)a) Majority of projects for engineering involves making Majority of projects for engineering involves making topographic map in a stereoscopic plotting unit.topographic map in a stereoscopic plotting unit. Wide angle photography (152mm focal length) is required for Wide angle photography (152mm focal length) is required for

topographic mapping because it provides better vertical topographic mapping because it provides better vertical accuracy.accuracy. If area is heavily wooded, use f=210mm (standard angle) to If area is heavily wooded, use f=210mm (standard angle) to

allow more visibility through trees.allow more visibility through trees. Generally 60% overlap with 15-30% sidelap.Generally 60% overlap with 15-30% sidelap. Orientation of flightlines is dictated more by economy than Orientation of flightlines is dictated more by economy than

geometric considerations.geometric considerations.

Elements of PlanningElements of Planning

b)b) Photos for mosaics should be flown as high as possible.Photos for mosaics should be flown as high as possible. Reduces relief displacement.Reduces relief displacement.

c)c) Orthophotos – similar to topo maps, however, should be Orthophotos – similar to topo maps, however, should be taken normal to ground topo. taken normal to ground topo.

2.2. Photo Scale: somewhat dependent on type of Photo Scale: somewhat dependent on type of plotter.plotter.

Essentially can be dependent on type of plotter you Essentially can be dependent on type of plotter you need to see and dividing it by the resolving power of the need to see and dividing it by the resolving power of the photo equipment.photo equipment.

Also affected by map accuracy and area configuration.Also affected by map accuracy and area configuration.

Elements of PlanningElements of Planning3.3. Allowed scale variation.Allowed scale variation.

Variation caused by difference in ground elevation and Variation caused by difference in ground elevation and flying height.flying height.

Longer focal length reduces scale variation.Longer focal length reduces scale variation. If flying height remains constant and ground elevation If flying height remains constant and ground elevation

increases the area covered by photo becomes less.increases the area covered by photo becomes less. Overlap becomes lessOverlap becomes less Viewfinder needed to control overlap and flightline spacing, thus Viewfinder needed to control overlap and flightline spacing, thus

eliminating possible gaps.eliminating possible gaps.

4.4. Relief displacementRelief displacement Affects mosaics most.Affects mosaics most.

Large amount of relief displacement will make it difficult to form Large amount of relief displacement will make it difficult to form continuous picture desired in mosaics.continuous picture desired in mosaics.

Elements of PlanningElements of Planning Relief displacement decreases as flying height Relief displacement decreases as flying height

increases, the focal length must also be increased.increases, the focal length must also be increased. Relief displacement has no adverse affect on map Relief displacement has no adverse affect on map

making with stereo.making with stereo. With greater relief displacement, elevations can be measured With greater relief displacement, elevations can be measured

and plotted more accurately.and plotted more accurately.

5.5. Tilt Tilt Amount in direction of flight (y tilt).Amount in direction of flight (y tilt).

Will cause overlap to be greater on one end than other.Will cause overlap to be greater on one end than other. Amount normal direction of flight (x tilt).Amount normal direction of flight (x tilt).

Will increase sidelap on one side and decrease on other.Will increase sidelap on one side and decrease on other. Y tilt corrected by viewfinder.Y tilt corrected by viewfinder. X tilt corrected by increasing planned sidelap.X tilt corrected by increasing planned sidelap.

Elements of PlanningElements of Planning

6.6. Crab and DriftCrab and Drift Crab – angle formed between flightline and edges of Crab – angle formed between flightline and edges of

photo in direction of flight and caused by not having photo in direction of flight and caused by not having focal plane square with direction of flight at time of focal plane square with direction of flight at time of exposure.exposure. Corrected by rotation of camera on vertical axis through Corrected by rotation of camera on vertical axis through

viewfinder.viewfinder. Reduces coverage, but sidelap compensates.Reduces coverage, but sidelap compensates.

Drift – plane not staying on flightline.Drift – plane not staying on flightline. Most common cause of re-flights and gaps.Most common cause of re-flights and gaps.

Elements of PlanningElements of Planning7.7. Flying height: determined after sidelap and Flying height: determined after sidelap and

overlap determined.overlap determined. Factors affecting:Factors affecting:

1.1. Desired scale, relief displacement, and tilt.Desired scale, relief displacement, and tilt.2.2. Precision of equipment used.Precision of equipment used.

Greater precision, greater possible flying height.Greater precision, greater possible flying height. By doubling flying height, ground coverage increased 4 By doubling flying height, ground coverage increased 4

times, thus less ground control and fewer photos.times, thus less ground control and fewer photos. Vertical accuracy most important in topographic Vertical accuracy most important in topographic

mapping.mapping.1.1. Flying height is related to contour interval desired.Flying height is related to contour interval desired.

Relationship called C-factor (precision factor)Relationship called C-factor (precision factor) Flying height = desired contour interval x C-factorFlying height = desired contour interval x C-factor C-factor is the value used to compute flying height which C-factor is the value used to compute flying height which

will produce photos satisfactory to obtain the desired will produce photos satisfactory to obtain the desired vertical accuracy of the maps.vertical accuracy of the maps.

Elements of PlanningElements of Planning8.8. Direction or orientation of terrainDirection or orientation of terrain

Arrange to fly along ridges, not across.Arrange to fly along ridges, not across.

2.2. Gathering material and people.Gathering material and people.1.1. Existing photos, maps, survey data, instruments Existing photos, maps, survey data, instruments

and personnel.and personnel.2.2. Determine specifications and Determine specifications and

conditions for operation.conditions for operation.3.3. Preparing f inal plans.Preparing f inal plans.

1.1. Scheduling Scheduling 2.2. Surveying instructionsSurveying instructions

2.2. Cost estimating and replanning.Cost estimating and replanning.

Flight DesignFlight DesignA.A. ConsiderationsConsiderations

1.1. Project boundariesProject boundaries2.2. Existing and planned controlExisting and planned control3.3. Time scheduleTime schedule4.4. Final product neededFinal product needed5.5. Optimum flying seasonOptimum flying season6.6. Found cover conditionsFound cover conditions

A.A. ObjectivesObjectives1.1. Determine optimum conditions for spacing of photos along Determine optimum conditions for spacing of photos along

flightlines.flightlines.2.2. Number and spacing of fligtlines to cover area.Number and spacing of fligtlines to cover area.3.3. Plan must account for allowable deviations.Plan must account for allowable deviations.4.4. Distance between flightlines on fllightway. Distance between flightlines on fllightway.

Flight DesignFlight Design

C.C. Flight PatternsFlight Patterns1.1. Totally dependent on overlap and sidelap.Totally dependent on overlap and sidelap.

Under ideal conditions with 9”x 9” photo with 6” focal Under ideal conditions with 9”x 9” photo with 6” focal length, and overlap of 57%, and sidelap of 13% will length, and overlap of 57%, and sidelap of 13% will provide maximum stereo coverage with no gaps.provide maximum stereo coverage with no gaps. If additional safety factor desired, overlap can be increased to If additional safety factor desired, overlap can be increased to

70-75% and sidelap can be increased to 50%.70-75% and sidelap can be increased to 50%.

Computation of Flight PlanComputation of Flight Plan► Data required to compute flight map lines, time Data required to compute flight map lines, time

interval between exposures, and amount of film interval between exposures, and amount of film needed.needed.

1.1. Focal length of camera.Focal length of camera.2.2. Flying height above datum or photo scale for certain Flying height above datum or photo scale for certain

elevation.elevation.3.3. Size of photo.Size of photo.4.4. Size of area to be photographed.Size of area to be photographed.5.5. Positions of outer flight lines with respect to boundary.Positions of outer flight lines with respect to boundary.6.6. Overlap.Overlap.7.7. Sidelap.Sidelap.8.8. Scale of flight map.Scale of flight map.9.9. Ground speed of aircraft.Ground speed of aircraft.

ExampleExampleArea – 15 miles N-S & 8.5 miles E-WArea – 15 miles N-S & 8.5 miles E-WPhotos – 9” x 9”Photos – 9” x 9”Save tobe 1:12000 @ 700’ above elevationSave tobe 1:12000 @ 700’ above elevationOverlap – 60%Overlap – 60%Sidelap – 35%Sidelap – 35%Ground speed of plane – 150 mphGround speed of plane – 150 mphFlight lines to be laid out N-S on a map @ a scale Flight lines to be laid out N-S on a map @ a scale

of 1:62500of 1:62500Outer flight lines coincide with E & W boundaryOuter flight lines coincide with E & W boundary

1.1. Flying Height:Flying Height:12000’ above 700’ or 12700’ above sea level12000’ above 700’ or 12700’ above sea level

2.2. Ground Distance Between Flight lines – since sidelap is 35%, photo Ground Distance Between Flight lines – since sidelap is 35%, photo distance between lines is 65% of 9”=5.85”distance between lines is 65% of 9”=5.85”

3.3. Number of flight linesNumber of flight linesTotal width = 8.5 miles x 5280 = 44880’Total width = 8.5 miles x 5280 = 44880’

flight lines (Round up)flight lines (Round up)

4.4. Adjust ground distance between flight linesAdjust ground distance between flight lines

5.5. Spacing of flight lines on flight mapSpacing of flight lines on flight map5610’ on map @ 1:62500 scale5610’ on map @ 1:62500 scale

'5850'1/"12

12000'85.5 =×=∴ ingGroundSpac

=∴= HH 12000

11

9185850

44880 =+=∴

'561019

44880 =−

"08.1'1

"12

62500

5610 =×

6.6. Ground Distance Between Exposures with 60% overlap gain onGround Distance Between Exposures with 60% overlap gain oneach photo is 40%each photo is 40%40% of 9” = 3.60” ground distance is:40% of 9” = 3.60” ground distance is:

∴∴ '3600

'1/"12

1200060.3 =×