Steps in Image Interpretation: Classification, Enumeration, Mensuration, and Delineation (Especially for GATE-Geospatial 2022)

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Classification is the assignment of object, features, or area to the classes based on their appearance on the images. Ultimately all the processing must be done based on the following image elements.

Implications of Spectral and Spatial Features to Improve the …

Steps in Image Interpretation

The image interpretation procedure is a complex task and requires several tasks to be conducted in a methodical manner which include:

  • Classification
  • Enumeration
  • Mensuration
  • Delineation

Classification: Three Levels of Confidence and Precision

Often the distinctions are made between three levels of confidence and precision namely- detection, recognition and identification. Detection is the determination of presence or absence of the feature.

  • Recognition implies a higher level of knowledge about a feature or an object such that the object can be assigned identity.
  • And, identification means that the identity of an object or feature can be specified with enough confidence and detail to place it in a specific class.

Enumeration

It is the task of listing or counting discrete items visible on an image.

Mensuration

Mensuration or measurement is an important function in many image interpretation problems. Two kinds of measurements are important:

  • First, is the measurement of distance and height, and by extension, volumes and areas as well.
  • A second form of measurement is quantitative assessment of image brightness.

Delineation

  • Finally, the interpreter must delineate, or outline, regions as observed on remotely sensed images. The interpreter must be able to separate distinct aerial units that are characterized by specific tones and textures and to identify edges or boundaries.
  • The image analyst may simultaneously apply several of these skills in examining an image. Recognition, delineation and mensuration may all be required as the interpreter examines an image.

Details of Image Interpretation

  • The requirements for image interpretation:
    • Remote sensing system
    • Knowledge of image and sensor characteristics
    • Proficiency based on knowledge of the subject and
    • Adequate familiarity of the geographic region and locality
  • Interpretation key is the criteria for identification of an object with interpretation elements. Image interpretation depends on the interpretation keys which an experienced interpreter has established from prior knowledge and the study of the current images.
  • Generally, standardized keys must be established to eliminate the differences between different interpreters. Image interpretation keys can be graphic and/or textual. They aid in identifying thematic classes from image feature characteristics. You will find that it is necessary at the beginning of a project, to design and construct a key to be employed in a specific study.

Process of Interpretation

  • Basically, interpretation keys can be one of two generic types: selective and elimination keys. Selective keys contain numerous example images with the supporting text.
  • The interpreter selects the example that most closely resembles the feature or condition found on the image being studied. Elimination keys are composed of word descriptions ranging through various levels of broad to specific characteristic discrimination.
  • Interpretation proceeds step by step from general to specific and leads to elimination of all features or conditions except the one being identified. Elimination key often takes the form of dichotomous key.
  • In dichotomous keys, interpreter makes a series of choices between two alternatives and progressively eliminates all but one possible answer. The analyst progresses down through this hierarchy, making choices at branching description paths. Finally, objects are identified by the process of elimination.

Example of Image Interpretation

  • An example of interpretation keys for forest mapping, Japan Association of Forestry given below:
Title: Image of Interpretation Keys
SpeciesCrown shapeEdge of crowntonePatternTexture
CederConical with sharp spearCircular and sharpdarkSpotted grainHard and coarse
CypressConical with round crownCircular but not sharpDark but lighter than cederSpottedLard and fine
PincCylindrical with shapeless crownCircular but not sharpLight and unclearIrregularly spottedSoft but coarse
LarchConical with unclear crownCircular with unclear edgeLighter than cypressSpottedSoft and fine
Fir/spruceConical with wider crownCircular with zigzag edgeDark and clearirregularCoarse
deciduousIrregular shapesUnclearlighterirregularCoarse

A sample of image interpretation keys used for interpreting for land cover mapping

Interpretation Keys

Developed by: