Photo Interpretation Visual

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Photo Interpretation (Visual)
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Overview

• Data that can be derived from Aerial Photo
• Photo interpretation (Visual)
• Difference
• Examples of Difference
• Interpretive elements
• 3D
• Types of interpretation
• Guides to interpretation
• Summary of Photo Interpretation

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Data that can be derived from Aerial Photo

• Distance (using ruler and scale of the photo)
• Angel (using protractor - Direction)
• Areas
• Height (3D contour using stereoscopy)
• Extraction of natural and artificial features

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Photo Interpretation

• Interpretation is based upon the concept of
  differentiation - the ability to identify a
  single element due to its difference with respect
  to background and/or surroundings
• Difference can be "measured" in three responses
  spatial, spectral, and temporal
• Visual interpretation is dependent on the skill
  of the operator, experience, and knowledge of the
  area
• Automatic classification (Digital) is based on
  using computers instead of human eye

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Difference

• Spatial related to dimension or location
  (includes size, shape, position, association)
• Spectral EM response (tone, colour as a result
  of reflection and emitted EM energy)
• Temporal change in spatial or spectral
  characteristics with time. Can be cyclic (daily,
  seasonal, annual) or "permanent" (eg. clearing,
  construction)

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Examples of Difference

• Object is big in size spatial Suitable image
  scale ?
• Water is similar to vegetation in Black White
  imagery from the visible band (dark tone) but
  different in the Near Infra Red spectral Portion
  EM spectrum to sense in ?
• In late summer, crop based agricultural activity
  is minimal due to the dry conditions. By spring
  crops are reaching their prime temporal what time
  scale / point is best to identify a specific
  feature ?

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Key interpretive elements

• Primary Size, Shape, Tone, Texture, Pattern
• Additional Site / Location, Association,
  Shadows, Stereoscopic Appearance

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Interpretive elements

• Shape General form, configuration or outline of
  individual objects, eg. regular, irregular,
  linear, curved, rounded, triangular etc. e.g.
  House, Round About
• Size The physical extent or dimension of a
  feature. May be comparative (relative) (eg. a big
  bird is still small compared to an elephant).
• Comparable Large, small, massive, tiny
• Magnitude kms, metres, microscopic,
  macroscopic
• Tone Relative brightness or colour of a feature
• Gray scalevery dark tone, dark tone, dark gray,
  mid tone, light tone, white
• Colour Blue, Green, Red, etc.

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Interpretive elements-continue

• Pattern Relates to the spatial arrangement of
  objects. Repetition of form or spectral response
  (tone) eg. gridded, regular (plantation), linear,
  irregular, ordered (hierarchal), symmetric,
  geometric etc. e.g. Agriculture, Orchard, Forest
• Texture Frequency of tonal change of the object
  eg. smooth, coarse, speckled, fine, fuzzy,
  soft.e.g. water appears as smooth while forest as
  coarse
• Site/Location physical position of object
  feature (topographic or geographic), hill slopes,
  ocean, land, mountains etc.

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3D

• Monoscopic (easier and quicker, flat area) versus
  Stereoscopic (number of photos, cost, purpose)
• Shadow Used to determine 3D information from a
  2D image, shape and height of object via shadow
• Shadows can enable objects to be "seen" when the
  natural conditions may not be favourable eg.
  power poles (small planimetric extent, can only
  be identified by shadow), sand dunes (shadows
  result in contrast, can see topographic outline)
• Appearance How the surface appears in 3D,
  generally related to surface consistency and
  change in height, eg. Object (Tall, spherical)
  and Area (Undulating, flat, rugged)

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Types of interpretation

• Generally there are two types of interpretation
• Selective (Descriptive, graphical, pictorial,
  sample images)
• Elimination (Dichotomous)
• The selective method provides the interpreter
  with a range of choices with accompanying
  information or descriptions (eg. feature
  characteristics such as tone, shape, texture
  etc). The interpreter simply refers to the object
  and then selects the choice that best matches
  that seen (eg. pictorial/graphical, sample
  images, descriptive text)
• The elimination method uses a structured
  "routing" process to reduce the classification to
  a minimum number of options (ideally only one).
  Usually simple 2 path decision making tree with
  only minor decisions to be made at each step

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Guides to interpretation

• Define the objective of the interpretationSimple
  (feature recognition) and complex (modeling)
• Identify the type of photos needed (B/W,
  Color_IR, Stereoscopic vs Monoscopic coverage,
  Temporal, Scale, Calibration / enhancement /
  rectification)
• Prepare an equipment that aid in interpretation
  e.g. magnifying lens, stereoscope - mirror
  stereo, pocket stereo, and digital visual system
• Have a good eyes, lateral thinking, and patience
• Acquaint yourself with the area Knowledge of
  phenomenon and area general, local, specific
• Follow a deductive process general examination
  of the image and concentration on specific
  features
• Check the consistency and reliability of
  interpretation by maps and ground truth data
  (Accuracy)

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Summary of Photo Interpretation

• Features on a photo can be delineated based on
  the following characteristics
• Tone (B/W -gray shade), color and brightness)
• Size (depend on scale e.g. size of house)
• Shape (geometrical arrangement, road/house)
• Texture (smoothness or roughness,water, grass)
• Pattern (spatial arrangement, network of streets)
• Shadow (height of object)
• Site (geographic location, features on rivers)
• Photo interpretation can be supported by
  magnifying lens and stereoscope (pocket, mirror)

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Photogrammetric Applications

• 3D analysis for environment
• 3D analysis enables users to create, analyse, and
  display surface data, which is important in many
  applications in the urban areas, for example,
  road, canal, dam, and simulation of air and water
  pollution. 3D data can be extracted from aerial
  photo directly (stereoplotters) which allow
  Photorealistic presentation with possibilities
  for navigation through the 3D city model (fly
  through) and animate on-screen designs
• Urban Growth
• Tracing socio-economic and physical pattern of
  urban development overt space and time is a key
  element for heritage and future development.
  Historical aerial photographs imagery can be
  classified and integrated with GIS to show the
  historical development of a city

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Aaerial photo Kuala Lumpur