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Click on any one of the links below to view a more complete definition and explanation of the term's use and meaning when talking about aerial photography.

  Any word or phrase that appears in ALL CAPITALS within the definitions below will also have a definition entry of its own.


Certification
     Letters of certification are typically used in legal proceedings.  They authenticate the photo or photos in question by explicitly stating many particulars, usually including such information as the original photographer, date the photo was taken, the approximate negative's scale, etc.  Also, a letter of certification often contains a statement that no intentional alterations have been made to the print, signed by a representative of the photography company.  Normally, a letter of certification will come attached to the photo product (or, in the case of those sources that will also certify DIGITAL IMAGEs, it may be attached to a printed representation of the image).

Note: Due to the more easily-modifiable nature of DIGITAL IMAGES, many sources will not offer letters of certification for them.

Contact Print
    A contact print is the equivalent of a proof, just like you might get from a portrait photographer. Therefore the print is the same size as the original NEGATIVE. Contact prints are made by putting the paper on the NEGATIVE (i. e. in contact with the NEGATIVE) and exposing the image directly, rather than projecting the image through a lens. Aerial photography is typically shot using large cameras with 9 inch square NEGATIVEs. Therefore a contact print is usually about 9"x9" and is useful as a final product just like a portrait photographer's 8"x10" print. Due to the process required to make photographic paper, contact prints cannot reproduce all the fine details originally captured in the NEGATIVE and so it might be necessary to enlarge or "blow up" the photo to see the desired details.

Diapositive
    A "diapositive" is a photo that is chemically developed in the same manner that a contact print is produced. It differs from a contact print, however, in that it is printed on a transparent sheet of plastic rather than photographic paper.  It is the aerial photography equivalent of a slide. It appears similar to a NEGATIVE, but the image is normal, i. e. the colors aren't reversed. Because the transparent sheet is made using almost the same technique used in camera film, diapositives can almost exactly reproduce the fine details originally captured in a NEGATIVE. They are typically used for examination of sites, such as map making. They can also be used with overhead projectors in presentations showing enlarged portions of an image on a wall similar to conventional slides. Also called "film positives" or "photo transparencies".

Digital Image
    An increasing amount of aerial photography is being taken with digital aerial cameras instead of traditional film cameras.  Like standard consumer handheld digital cameras, these cameras do not produce film-based NEGATIVEs, but instead record the image as a computer file.
    Also, NEGATIVEs taken with film-based cameras can be scanned with special large format scanners and recorded as a computer image file with results similar to (usually superior to) photos taken with digital cameras.  Digital images can be printed out on standard computer printers or printed with a special process that produces traditional chemically-produced prints.  Digital images can also be viewed on a computer screen instead of or in addition to being printed.  Sometimes conditions such as lost or destroyed NEGATIVEs force digital images to be produced from existing paper prints.  Also called "scans" or "digital scans".


Digital Print
    Instead of a photo being developed from a negative by a chemical process, a digital print is a photo produced from a computer image file that has been made either by scanning a negative (or transparency), or by having been originally taken with a digital camera.  The quality of digital prints varies depending upon the equipment used, the resolution the picture was scanned or shot at, and the type of printing equipment.
    When NAR produces a digital print from a negative or transparency, we can scan at resolutions from 1200 Dots Per Inch to 2000 DPI.  The printing equipment we use has the ability to print a 1:1 scale photo (i.e. at its original size, not an enlargement) on photographic paper that can be viewed under magnifications up to 12X without any appreciable "pixelation" (digital degradation).  These prints, therefore, are equal in quality to a standard, chemically-developed print.

Duplicate Negative
    A copy of the original NEGATIVE  Production of NEGATIVEs is done through standard chemical photographic processing methods.  These methods are not digital, but analog in nature and therefore can't produce exact copies of the original NEGATIVE.  Proper duplication techniques, however, produce nearly exact copies of the original NEGATIVE and are considered identical for all but the most exacting examinations.

Enlargement Print
     A print made by magnifying portions of or the entire original image is commonly known as a "blow-up" and more correctly referred to as an "enlargement print" (or "enlargement" for short).  Aerial photography is taken with "large-format" cameras.  The difference between large formats and small or standard formats is the size of the original image that is captured.  In traditional, chemically-produced photography, this is the difference in the size of the NEGATIVEs.  A standard small format camera typically takes pictures using 35mm (approx. 1.4 inch) NEGATIVES.  In contrast, a large-format aerial photography camera typically takes pictures using 229mm (approx. 9 inch) NEGATIVES.   It is due to the camera lens' dense packing of imagery in the NEGATIVE that allows very detailed images to be captured on such relatively small NEGATIVE sizes.
    The size of the NEGATIVE tends to be somewhat hidden to the small-format photography customer.  Typically the customer thinks of the standard print size as 4"X6" and a blow-up or enlargement as a larger image, such as 8"X10".  In reality, any print that is not the size of the NEGATIVE (say 35mm in size) is an enlargement.  Prints this size are not very useful in small-format photography (approx. 1.4 inch).  But, in large formats, such as aerial photography, an unenlarged print is 229mm square (9"X9") and appears to be similar to a small format camera's 8"X10" enlargement.
    Since small-format, especially 35mm, photography is more common than large format, the apparent similarity between 8"X10" enlargements and 9"X9" "CONTACT PRINTs" often confuses customers into thinking they have received an enlargement.  In fact, just as a 35mm NEGATIVE can produce clear enlargements at up to 8 times (the number of times an 8"X10" print is blown-up to) so to can the 229mm negative of the aerial camera.  In fact, it's possible to enlarge the entire aerial photograph 5X to a size of approximately 4 feet square.  Smaller portions of an aerial photograph can commonly be enlarged as much as 15 to 20 times.
    The advent of digital photography into the aerial photography field has broadened the number of methods, product types, and levels of quality available to the customer.  For purposes of discussion, we classify the clarity of detail which can be seen in a given enlargement print into 3 grades: Presentation, Review, and Examination.
 
Fiducial(s), or Fiducial Point(s), or Fiducial Marker(s)
    An aerial photography camera "stamps" a markermost often a black shape of some kindin the corner and/or center of the each outer edge of every FRAME that it takes.  These shapes are called "fiducial points", and are used to help properly align the photos and make measurements of terrain details which the photos depict.

Film Positive
    Another term used for a DIAPOSITIVE.

Flight Line
    Under most circumstances, an airplane taking aerial photography will travel in a straight line while shooting pictures at regular intervals.  This straight line of photos is referred to as a "flight line".  When a large area (often a large square of rectangle) is photographed, the whole is usually comprised of several flight lines. This is because when the air plane has flown the length of the first line, it then changes course and flies back in the opposite direction, taking the next row of pictures, making another flight line.  In this way a whole area is covered with rows of flight lines that alternate back and forth in opposite directions.

Frame

    An individual photo is often called a "frame".

Identification Bar
    A line of data, usually printed along an outer edge of a photo, which lists information that is used to identify the photo.  The identification bar will usually list the photo's roll and frame number, and will often times also include other useful data, such as the original project code of the company that shot or commissioned the  taking of the photos, and even the photo's scale.  This information can be very important when trying to locate the current owner of a given photo or to re-order a new copy of a photo already known to exist.  Many times the data listed on an identification bar is all that is required to locate and order a new copy of a given photo.

Monoscopic Photography
    Monoscopic photography is the opposite of stereo photography.  Instead of taking pictures with a high degree of STEREO OVERLAP, as with STEREO PHOTOGRAPHY, monoscopic photos are taken far enough apart that there is almost no amount of shared ground area (STEREO OVERLAP) between one photo and the next along the same FLIGHT LINE.  Monoscopic coverage, therefore, cannot be used to see areas in 3-dimensions, because it lacks the two different perspectives that combine to create the illusion of depth which the STEREO OVERLAP of STEREO PHOTOGRAPHY provides.
           SEE Stereo Photography for a more detailed explanation of how stereoscopic photography works.

Negative
    Briefly stated, a negative is the original print made in traditional photography on a transparency as a reversed version of the image.  A more detailed description requires a little background first.
    Traditional photography, as opposed to digital photography, uses a chemical process to capture images and store them on a specially-coated surface.  The chemicals respond to light by absorbing it, becoming dark as a result.  The brighter the light the chemical is exposed to, the darker the chemicals in the coating become.  Therefore, the captured image looks exactly the opposite from the original source (i. e. shadows are light, and light sources are dark).  The original image is called a "positive" image and the opposite image is called a "negative" image, just like in arithmetic where a negative number is the opposite of the positive number.  Photographers want to show what the real world looked like at the time the picture was taken and so the positive image is the important one.  The negative image proved to be a useful method of achieving this when making multiple copies of the photo.  If a transparent surface, such as glass or plastic, was used to capture the negative image, passing light through the negative image onto another chemically-coated surface, such as a piece of paper, would produce a positive image (i. e. the light shadows of the negative image are now dark again.)  Most traditional photography, and therefore virtually all historical aerial photography, was taken in negative form. 

Negative Scale
              SEE Scale, Photo Scale, Print Scale, or Negative Scale for a full explanation.

Photo Scale
              SEE Scale, Photo Scale, Print Scale, or Negative Scale for a full explanation.

Photo Transparency
    Another term used for a DIAPOSITIVE.

Print Scale
              SEE Scale, Photo Scale, Print Scale, or Negative Scale for a full explanation.

Scale, Photo Scale, Print Scale, or Negative Scale
    Photo scale (often simply referred to as "scale") is a general term used to refer to the size of objects depicted in a photo image compared to the actual size of the object in the real world.  Scales are normally listed in either a standard ratio such as 1:20,000 (meaning 1 unit measured on the photo represents 20,000 units in the real world) or in inches-to-feet form such as 1"=1600' (meaning 1 inch measured on the photo represents 1600 feet in the real world). Therefore, a standard 9" x 9" square aerial photo at a scale of 1"=2000' shows an area 18,000' (about 3.40 miles) wide by 18,000' long. As an example of how to use scales, if a building is 500 feet long and the scale of the photo is listed as 1"=2000', then the building depicted in this photo would be 1/4 of an inch long because 500' is 1/4 of 2000', so the depiction is 1/4 of 1 inch.
    Photo scales are also called "print scales" or "negative scales" when a particular photo image is being referred to in order to be more specific.  A negative scale means the scale the photo was originally taken at.  So, the scale is the measure of objects in the image's NEGATIVE compared to the real world.  This differs from the print scale at times when the print is a blow-up (see ENLARGEMENT PRINT).
  It is almost always possible to have enlargements, or "blow-ups", made that will make objects in the photo larger and easier to see.  When an enlargement is made, the scale of the photo changes based on how much the photo was enlarged.  Because of this, the print scale is the measure of objects in a print made from the image's NEGATIVE compared to the real world.  So if a 10X enlargement was made from the NEGATIVE in our above example with the 500 foot long building,  the print scale would become 1"=200', and the depiction of the building would become 2 1/2 inches long.

Stereo Mate
    A single photo which shares a portion of  STEREO OVERLAP with another photo to produce a STEREO PAIR.
         
SEE Stereo Photography for a more detailed explanation.

Stereo Overlap
    The portion of coverage shared by a pair of stereoscopic photos, in which each portion covers the same area of ground from slightly different angles.
          SEE Stereo Photography for a more detailed explanation.

Stereo Pair
    A set of two stereoscopic photos that share the same portion of STEREO OVERLAP.
          SEE Stereo Photography for a more detailed explanation.

Stereo Photography
    Stereoscopic photography, or "stereo photography", is photography that is taken so that each photo shares a portion of coverage with the next photo along a FLIGHT LINE.  In this way, the area which one photo shares with the next is taken from a slightly different angle. When properly viewed, the two different angles combine to create an illusion of depth in the photography.

Stereoscopic Photography
         SEE Stereo Photography for a full explanation.

Stereo Viewer
    A device that is used to assist in properly viewing the 3-D effect of  the STEREO OVERLAP of a STEREO PAIR.


























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