Photogrammetry ' Lecture 13

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• Lecture 13 Content

• Photo Interpretation
• (Continued)
• Systematic interpretation in photo-interpretation

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• Systematic interpretation in photo-interpretation
• Successful interpretation of aerial
  interpretation depends on three factors
• Reference level
• That is the knowledge of the area by interpreter
• Purpose and content
• Refers to the specialist knowledge in map-making
• Image characteristics
• Specialist knowledge in photographic
  interpretation

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• Reference level
• Anyone looking at a photograph is doing an
  interpretation
• There will be differences in interpretation
• The differences in the capacity for
  interpretation are the result of the differences
  in knowledge possessed by different interpreters
• A reference level is needed
• Defined as the amount of knowledge stored in the
  mind of any person interpreting photographs

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• The reference level required by the interpreter
  is thorough understanding of physical and
  cultural features
• Therefore, the interpreter must be well
  acquainted with the area being interpreted
• Is achieved by studying maps and reading reports
  of previous surveys of the area

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• Purpose and content
• map content should meet the needs either present
  or anticipated
• Best decided by the client, the contractor, and
  comparison with other map series and after
  discussion with
• Map users
• Military services
• Public utilities
• Legal authorities
• And so on
• Final list of specification is derived and is
  used by the interpreter

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• Image characteristics
• Use of the 8 image characteristics
• Each image can be defined in terms of its
  characteristics

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• Other aid for interpretation
• Stereoscopic viewing
• To extract the maximum information with any
  degree of certainty
• Magnification
• Assist to identify small images but there are
  limitations as to the degree of magnification
• Comparative photography
• Other photographs of the same area especially if
  it is of a different scale
• Other references
• Existing maps, field reports, and other reports
  of the area
• Experience
• Both the area concerned and the technique of
  photo interpretation

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• Convergence of evidence
• Photographic interpretation is a deductive
  process
• Features that can be identified and recognized
  lead to the interpreter to the location and
  identification of other features
• The principle of convergence of evidence allows
  the interpreter to make use of clues to identify
  unknown objects

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• Most of the clues point to the same conclusion
  which is probably correct
• Deductive photographic interpretation requires
  conscious or unconscious consideration of the
  characteristics of image interpretation
• The completeness and accuracy of interpretation
  are proportional to the interpreters
  understanding of how and why images show the 8
  image characteristics

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• Photographic interpretation is an art of
  probabilities
• Interpretation is to photogrammetry as statistics
  is to mathematics
• When all evidence has been considered they may
  safely be regarded as being correct

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• The principle of convergence of evidence requires
  first to recognized basic features or types of
  features and then to consider their arrangement
  in the given context
• Critical examination of the evidence usually show
  that all interpretations but one are unlikely or
  impossible

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• Interpretation Procedure
• Field completion

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• Interpretation Procedure
• Seen as a process that can be divided into a
  number of phases
• Three phase operation
• Examination of the photographs
• Identification of objects or features
• Classification of objects identified

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• General Examination
• Of the block
• Of individual pairs
• To establish general characteristics of the
  whole area and detect parts having special
  significance

Identification Detailed examination aimed at the
detection and positive identification of
particular features
Classification Of particular features. May
involve decisions on generalization
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• Phase 1 Examination
• General examination of the photos
• Work from the whole to the part
• Interpreter becomes acquainted with the area in
  very general terms in order to improve his
  reference level
• General patterns of relief, vegetation and
  cultural developments are noted

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• Examining of the stereo-pairs is done in a
  systematic way of scanning
• Areas of the image in which relevant features are
  most likely to occur are singled out and examined
  first
• From this the remainder of the image is
  systematically scanned for logical search which
  adheres to the map specification regarding the
  intended content

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• Phase 2 Identification
• Photographs are examined in detail so that
  features are detected and identified which is
  a two phased procedure
• The reference level of the interpreter and image
  characteristics play an important role in order
  to obtain clues for identification

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• Phase 3 Classification
• Cannot be separated form Phase 2 and is an
  extension of Identification
• Can be thought as a more precise identification.
  Example identify roads and classify them as
  principal tracks as secondary
• The interpreter must perform some generalization
  work during interpretation

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Map specification
Examination Of photographs
Image Characteristics Tone Texture Pattern Shape S
ize Shadow Situation Association
Reference level
Detection of features
Identification of features
Not significant
Classification Of features
Not significant
Significant
Representation
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• Field completion
• All topographic mapping projects require field
  completion
• Necessary information for the compilation of a
  topographic map is divided into two categories in
  the planning stage
• The information acquired by means of photographs
• The information to be obtained by field work

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• After plotting, a reproduction of a manuscript
  on stable material is to be taken to the field in
  order to verify interpretations
• Additional features, not visible on the
  photographs, can be added to the plotting
• Features added are for example
• Objects that are small, obscured by other
  objects, or forgotten objects during the plotting
• During fieldwork further classifications are
  done, special purpose buildings are identified,
  and name are collected which will be required for
  the map

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• The End