Photogrammetry. Introduction ► Definition of Photogrammetry: the art, science, and technology of...

PhotogrammetryPhotogrammetry

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 information about physical objects and the environment by photographic and the 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 mapping procedure yet developed for most large projects.most 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 from 1:1,000,000 1:120 with contour intervals as small as 1 foot.intervals 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..


►Uses: Aerial photosUses: Aerial photos Aid: geological investigations, soil Aid: geological investigations, soil

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

Mathematical methods have been Mathematical methods have been developed to make precise 3-dimensional developed to make precise 3-dimensional measurements from photos.measurements from photos.►Phototriangulation: 3-dimensional positioning Phototriangulation: 3-dimensional positioning

of survey stations.of 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, human hearts, large radio telescopes, ships, dams, buildings and very accurate ships, dams, buildings and very accurate reproductions.reproductions.

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


►Photogrammetry cannot be used Photogrammetry cannot be used successfully over the following types successfully over the following types of terrain.of terrain. Deserts or plains, sandy beaches, and Deserts or plains, sandy beaches, and

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

Deep canyons or high buildings that Deep canyons or high buildings that conceal ground surface.conceal 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 measurements from photos from which ground positions, elevations, which ground positions, elevations, distances, areas, and volumes can be distances, areas, and volumes can be computed and topographic or computed and topographic or planimetric maps can be made.planimetric maps can be made.

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

Types of PhotogrammetryTypes of Photogrammetry

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

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

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

HistoryHistory

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

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

► Laussedat (French) – father of Laussedat (French) – father of photogrammetry.photogrammetry.

► 11stst in N. America – Deville, Surveyor General in N. America – Deville, Surveyor General of Canada.of Canada.

► U.S.G.S. adopted photogrammetry as U.S.G.S. adopted photogrammetry as mapping process in 1894 – mapping border mapping process in 1894 – mapping border between Canada and Alaska.between 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 Used extensively in WWI – photo

interpretation.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 Photogrammetry for EngineeringEngineering

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

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

Basic Categories of Basic Categories of Photogrammetric InterpretationPhotogrammetric Interpretation►Metrical Photogrammetry – obtaining Metrical Photogrammetry – obtaining

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

►Photo interpretation – evaluation of Photo interpretation – evaluation of existing features in a qualitative existing features in a qualitative manner – timber stands, water manner – timber stands, water pollution, soils, geological formations, pollution, soils, geological formations, crops, and military interpretation.crops, and military 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 projected through a central point, due to points being at different elevations, to points being at different elevations, they look 3 dimensional.they look 3 dimensional.

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

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

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

inches or mm.inches 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)]

ff

HH’’

ff

H-H-hh

Scale of a Vertical PhotoScale of a Vertical Photo

►Datum Scale = the scale which would be Datum Scale = the scale which would be effective over entire photo if all points were effective over entire photo if all points were projected downward to datum.projected downward to datum.

SSD D ==

► Average Scale = for photo planningAverage Scale = for photo planning

SSAV.AV. = =

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

ff

HH

ff

H-H-hhav.av.

Relief DisplacementRelief Displacement

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

d = radial distance to top of object-radial d = radial distance to top of object-radial distance to bottom of object.distance to bottom of object.

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

d d (H’)(H’)

rr

Planning and Executing Photo Planning and Executing Photo ProjectProject

► Basic Overall Process:Basic Overall Process:1.1. Photography – obtain suitable photos.Photography – obtain suitable photos.

2.2. Control – obtain sufficient control through Control – obtain sufficient control through field surveys and/or extension by field surveys and/or extension by photographic methods.photographic methods.

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

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

5.5. Final Map Drafting Final Map Drafting

Elements of PlanningElements of Planning

1.1. Conversion of requirements to Conversion of requirements to project specs.project specs.

Factors:Factors:1.1. Purpose of photogrammetryPurpose of photogrammetry

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

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

angle) to allow more visibility through trees.angle) to 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 Orientation of flightlines is dictated more by economy

than geometric considerations.than geometric considerations.


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

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

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

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

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


3.3. Allowed scale variation.Allowed scale variation. Variation caused by difference in ground elevation Variation caused by difference in ground elevation

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

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

spacing, thus eliminating possible gaps.spacing, thus eliminating possible gaps.

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

Large amount of relief displacement will make it difficult Large amount of relief displacement will make it difficult to form continuous picture desired in mosaics.to form 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 With greater relief displacement, elevations can be

measured and plotted more accurately.measured 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.


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

edges of photo in direction of flight and caused edges of photo in direction of flight and caused by not having focal plane square with direction by not having focal plane square with direction of flight at time of exposure.of flight at time of 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 By doubling flying height, ground coverage

increased 4 times, thus less ground control and increased 4 times, thus less ground control and fewer photos.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 C-factor is the value used to compute flying height

which will produce photos satisfactory to obtain the which will produce photos satisfactory to obtain the desired vertical accuracy of the maps.desired 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, Existing photos, maps, survey data,

instruments and personnel.instruments and personnel.

3.3. Determine specifications and Determine specifications and conditions for operation.conditions for operation.

4.4. Preparing final plans.Preparing final plans.1.1. Scheduling Scheduling 2.2. Surveying instructionsSurveying instructions

5.5. Cost estimating and replanning.Cost estimating and replanning.

Flight DesignFlight DesignA.A. ConsiderationsConsiderations

1.1. Project boundariesProject boundaries

2.2. Existing and planned controlExisting and planned control

3.3. Time scheduleTime schedule

4.4. Final product neededFinal product needed

5.5. Optimum flying seasonOptimum flying season

6.6. Found cover conditionsFound cover conditions

B.B. ObjectivesObjectives1.1. Determine optimum conditions for spacing of Determine optimum conditions for spacing of

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

increased to 70-75% and sidelap can be increased to increased to 70-75% and sidelap can be increased to 50%.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 interval between exposures, and amount of film needed.film 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 Positions of outer flight lines with respect to boundary.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.

ExampleExample

Area – 15 miles N-S & 8.5 miles E-WArea – 15 miles N-S & 8.5 miles E-W

Photos – 9” x 9”Photos – 9” x 9”

Save tobe 1:12000 @ 700’ above elevationSave tobe 1:12000 @ 700’ above elevation

Overlap – 60%Overlap – 60%

Sidelap – 35%Sidelap – 35%

Ground speed of plane – 150 mphGround speed of plane – 150 mph

Flight lines to be laid out N-S on a map @ a Flight lines to be laid out N-S on a map @ a scale of 1:62500scale of 1:62500

Outer flight lines coincide with E & W Outer flight lines coincide with E & W boundaryboundary

1.1. Flying Height:Flying Height:

12000’ above 700’ or 12700’ above sea 12000’ above 700’ or 12700’ above sea levellevel

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

3.3. Number of flight linesNumber of flight lines

Total 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 map

5610’ 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 on

each 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

Photogrammetry. Introduction ► Definition of Photogrammetry: the art, science, and technology of...

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