Presentation on theme: "Selected Characteristics of NRI Aerial Photos … a brief introduction …"— Presentation transcript:
Selected Characteristics of NRI Aerial Photos … a brief introduction …
Characteristics of NRI Aerial Photos A Few Selected Terms Formats, Spectral Sensitivity, and Scale Scale, Flying Elevation, and Footprints Fiducials and Other Photo Markings Intro to Photo Geometry and the Single Point Perspective Resolution Orientation of Photos for Scanning Use, Care and Storage of Photos
A Few Aerial Photo Terms Frame (also known as Metric or Mapping) Cameras Shutter exposes the entire frame at a single instant Calibrated in a laboratory to determine internal geometry focal length lens distortion 9 inch by 9 inch film
A Few Aerial Photo Terms Focal Length Distance (along the optical axis) from the camera lens to the plane of sharpest focus Lens Focal length
A Few Aerial Photo Terms Vertical Photography Camera axis is < 3° from vertical Oblique Photography Camera axis is > 3° from vertical Low obliqueno horizon High obliqueincludes horizon Camera Axis
Aerial Photo Formats, Spectral Sensitivity & Scale Formats: Color film positive One photo per NRI site Monoscopic Spectral Sensitivity: Natural color Color Infrared Scales: 1:7,920 1:12:000 1:15,840
Scale, Flying Elevation, and Ground Distance lens elevation 7,920 ft 6,000 ft 3,960 ft Photo Scale = focal length/height above ground 1:7,920 = 6/3,960 1:12,000 = 6/6,000 1:15,844 = 6/7,920 Ground Distance = Photo Distance/Photo Scale 5,940 = 9/1:7,920 9,000 = 9/1:12,000 11,880 = 9/1:15,840 5,940 9,000 11,880 Not to scale
Photo Footprints Map Footprint: the perimeter of the area covered by an aerial photo. Small Scale Footprint (large area covered, features appear small) Large Scale Footprints (small area covered, features appear large)
NRI Aerial Photography Footprints Approximate Coverage of NRI Photos 1:7,920 5,940 x 5, acres 1:12,000 9,000 x 9,000 1,860 acres 1:15,840 11,880 x 11,880 3,240 acres Nominal 160 acre area segment
FiducialsFiducials Fiducials: permanent reference points exposed onto the photograph. Principal Point (PP): Center of photofound by intersection of lines drawn between opposing fiducials. Nadir: image of point directly below airplane at time of photo (Nadir will equal PP for vertical photos).
Data Strip: varies in appearance and location by camera, but usually contains an altimeter and clock. Other Photo Markings - Data Strip altimeterclock
State FIPS Code CountyState Segment # Nominal Scale to nearest Not to be trusted for measurements! Agency NameDate NOTE: Standard title block info is oriented to the North on NRI photographs. Other Photo MarkingsStandard Title Block
State Segment # Nominal Scale to nearest Not to be trusted for measurements! Agency Name Date Other Photo MarkingsAutomated Title Block County FIPS North Arrow Time EXAMPLE 1
State Segment # Nominal Scale to nearest Not to be trusted for measurements! Agency Name Date Other Photo MarkingsAutomated Title Block FIPSNorth Arrow EXAMPLE 2 Latitude and Longitude of photo center
Other Photo MarkingsCamera # and Focal Length Camera #Focal length mm Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. EXAMPLE 1
Other Photo MarkingsCamera # Camera # Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. EXAMPLE 2
Other Photo MarkingsCamera # and Focal Length Camera # Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. EXAMPLE 3 Focal length mm
Photo Geometry--Single Point Perspective
If scale and orientation are known, distances and bearings can be measured directly: Photo scale varies with relief and objects at different elevations are displaced relative to one another, thus distances and bearings are more difficult to measure directly:
Photo Geometry--Single Point Perspective The photo scale is different at the tops of the buildings than at the street level. The tops of the building are displaced radially outward relative to their location at the street.
Photo Geometry--Single Point Perspective More than just buildings… The clearcut boundaries (right) are straight lines on the map and ground Higher elevations are displaced radially outward (relative to lower elevations)
Photo Geometry--Single Point Perspective Distortion: error resulting from lens imperfections, camera tilt, poor camera vacuum, etc. Displacement: the result of projecting a 3-D world (with varying heights) on a 2-D surface from a single point perspective. Allows for stereo viewing, however, NRI photos are not acquired in stereo Orthorectification: For the NRI, scale variation, relief displacement, camera orientation, and lens distortion must be removed for accurate measurement of lengths and areas.
Original PhotoOrthorectified Photo Photo Geometry--Orthorectification
Resolution of Aerial Photography Resolution Smallest feature which can be detected With film, resolution is expressed as Line pairs per millimeter (lp/mm) or Ground Resolved Distance (GRD) Photography has the most resolving power of any remote sensing system Mapping frame cameras and films used for the NRI under ideal conditions can typically resolve about 100 lp/mm GRD = reciprocal of image scale/system resolution. Example: the calculated GRD of a 1:7,920 NRI photo is 7,920/ (100 lp/mm) = GRD 79.2 mm or 3.1 inches Digital or scanning resolution is expressed as Ground Sample Distance (GSD) which is the size of the pixel in ground units GSD = reciprocal of image scale/scanning resolution Example: the calculated GSD of a 1:7,920 NRI photo is 7,920/600 dpi = GSD 13.2 inches
Resolution of NRI Photos at Various Scales ScaleGRS 100 lp/mm GSD 600 dpi scan 7, , ,
MicroTeck 9800XL Scanner Considerations Standard desktop scanners like the MicroTek 9800XL can do an excellent job of scanning NRI photography. Limitations of desktop scanners for NRI include: Less geometric accuracy than photogrammetic scanners No option for unattended roll film scanning Advantages of desktop scanners for NRI include: Cost $1,800 vs. $100,000+ for a photogrammetric scanner Geometric accuracy acceptable for natural resource projects The MicroTek is capable of scanning at 1,600 dpi, but testing has shown that 600 dpi is adequate for the NRI.
Orientation of Film on the Scanner All NRI photos are scanned with North to the top. The relationship of North to the film markings varies depending on: Flying direction. NRI photos can be flown North-South, South-North, East-West, or West-East. Type of camera The following slides will help you determine the proper orientation.
Top of the Scanner The front of the scanning bed is considered the top. Place the North end of the photo face down toward front of the scanner Place North Edge Here
The NRI photography contract specifies that the photo is to be titled on the North edge. What to scan? Scan the entire piece of film including the data strip and fiducial marks. North Edge – Standard Title Block – Example 1 Standard Titling on North Edge
The NRI photography contract specifies that the photo is to be titled on the North edge. Notice that this photo has the data strip on the opposite end from the previous slide. What to scan? Scan the entire piece of film including the data strip and fiducial marks. North Edge – Standard Title Block – Example 2 Standard Titling on North Edge
Automated titling varies. Look for the North arrow to determine the correct orientation. What to scan? Scan the entire piece of film including the data strip and fiducial marks. North Edge – Automated Titling – Example 1
Automated titling varies. Look for the North arrow to determine the correct orientation. What to scan? Scan the entire piece of film including the data strip and fiducial marks. North Edge – Automated Titling – Example 2
Automated titling varies. Look for the North arrow to determine the correct orientation. Notice this is actually a West arrow. The photo is oriented correctly with West to the left and North to the top. What to scan? Scan the entire piece of film including the data strip and fiducial marks. North Edge – Automated Titling – Example 3
Use, Care and Storage of Aerial Photos Proper Handling of Photographic Materials Cleaning Storing and Archiving Additional Notes
Proper Handling of Photographic Materials Things you can do to protect your photographic materials… Keep your work environment and tools clean Wear lint-free gloves Keep photos in protective sleeves Store photos under the best possible conditions Have copies made if you plan to use them in the field Keep transparencies clean REMEMBER! The NRI photo transparency is the original film from the camera. No backup copies exist. If you have to ship an original NRI photo, use FedEx and declare a value
Proper Handling of Photographic Materials What can damage photographic materials? Fingerprints, dirt, dust, moisture, mold and prolonged exposure to lights can threaten their quality or worse, render them useless.
Cleaning and Repairing Photographic Materials Acceptable Cleaning Materials Cotton Fabric White or light colored Anti-static cloths are ok as well Soft-Bristled Brushes Flat, camels hair Create a static charge by brushing the bristles over a plastic rod such as a pen Compressed Air Make sure the air is filtered to avoid sandblasting and oil spots Solvents Isopropyl alcohol98% purity or higher!!! Ethyl alcohol98% purity or higher!!!
Cleaning Photographic Materials Good ventilation and sufficient air flow Use soft, lint-free cleaning fabric (cotton) Test a discrete area before you begin Moisten, clean and re-moisten with solvent DO NOT SATURATE YOUR PHOTOGRAPH! Clean one small area at a time Repeat if needed, but be conservative in your cleaning approach!
Protect from light sources Use proper storage containers i.e., metal or archival grade safe boxes Do not stack or pack tightly to avoid pressure on your prints and negatives Interleave them with acid-free paper Use moisture-proof storage envelopes Control temperature and humidity Avoid storing them near heat sources or ozone-generating machines i.e., photocopiers Silica gel packets help to dehumidify Storing and Archiving Photographic Materials Packing Materials Use proper storage containers i.e., metal or archival grade safe boxes Avoid using original packaging it will break down over time and damage your photographic materials Storage Location Main or upper floors and at least 6 inches (15 cm) above the floor Protect against fire Fireproof storage vaults Fire cabinet or safe They must be able to prevent temperatures from rising above 100°F (38°C)
Additional Notes Unlike unprocessed film, prints are not affected by x-rays i.e., airport security Do not store black and white and color negatives together in the same envelope Do not use markers to write on the film or protective sleeve!
SummarySummary Brief introduction to photo characteristics Formats, film types, range of scales Footprints Photo Markings (title block, fiducials, focal length) Photo Geometry Scale varies with relief Radial displacement Photo Resolution Orientation for scanning Proper Storage