Remote Sensing and Image
InterpretationBy: Lokender Yadav
contents
Introduction Map as a model Spatial elements and terminology Classification of Maps Map Scale Spatial referencing system Computers in map production General software’s in map production Types of data products
Continued ……Continued ……
Image interpretation strategy Levels of interpretation keys Topography Types of Drainage pattern and Texture Erosion Process of image interpretation Basic elements of image interpretation Overview on visual image interpretation
equipment
Map as Model Representation of features of earth drawn to scale “A map is a very powerful tool and maps are typical
reductions which are smaller than the areas they portray” (Robinson et.al 1984)
Spatial elements and terminology Spatial objects in the real world can be thought of as
occurring in four easily identifiable types namely, points, lines, areas and surfaces
Points, lines and areas can be represented by using symbols to depict the real world.
Surfaces are represented by any combination of these spatial entities.
In general, all the geographic surfaces are in two tangible forms, namely, discrete and continuous.
Trees, houses, road intersections and similar items are
discrete spatial features.
Classification of Maps
On the basis of scale Small scale map Large scale map- urban plan map, transportation
and network map
Map Scale
The ratio between the reduced depiction on the map and the geographical features in the real world is known as the Map Scale
Scale expressed in three ways:
◦ Fractional scale-the method of representing this type of scale is called representation fraction method
In India commonly used fractional map scales are 1:1,00,000,00; 1:250,000, 1:50,000; 1:25,000 and 1:10,000
Graphical Scale- A line printed on the map and divided into units that are equivalent to some distance
The measured ground distance appears directly on the map in graphical representation
Verbal Scale- This is an expression in common speech like “an inch to a mile”
Spatial referencing system
To locate objects with respect to some reference system
Methods of spatial referencing systems◦ Geographic coordinate systems-
Denoted by latitude and longitude
◦ Rectangular coordinate systems(RCS) Spatial data are in two-dimensional form Relative position- location of any point on the earth’s surface w.r.t
RCS
◦ Non- coordinate systems Spatial reference with descriptive codes such as postal codes which
is numeric in nature
Computers in map production Advantages
To make existing maps more at a quicker pace
To make existing maps at a cheaper rate
To make maps for specific user needs
To make map production possible in situations where skilled staff are unavailable
To allow experimentation with different graphical representations of the same data
Continued… To facilitate map making and updating when the data are already
in digital form
To minimize the use of the printed map as a data store and thereby to minimize the effects of classification and generalization on the quality of the data
Introduction of automation can lead to a review of the whole map – making process , which can also lead to savings and improvements
General software’s in map production
Arc- GIS ARC- VIEW etc.
Types of data productsDepending on correction applied & level of processing
Note: FCC are generated by combininig the data contained in three spectral bands respectively. The choice of band combinations can be determined depending upon application
Image interpretation strategyVisual image interpretation : Process of
indentifying what we see on the images and communicate the information obtained from these images to others for evaluating its significance
Includes relative locations and extents
Use of data products like Satellite single band imageries, FCC for performing image interpretations to extract thematic information for subsequent input to GIS
Levels of interpretation keys Interpretation Keys: Criterion for identification
of an object with interpretation elements
Basic elements of image interpretation
Size
Size of objects in an image is a function of scale
Proper photo scale selected depending on the purpose of interpretation
Most commonly measured parameters:- length, width, perimeter, area and occasionally volume
Shape
Shape of an object is described as the geometric form represented form represented on an image
Regular shapes are signs of man-made objects
Irregular shapes with no distinct geometrical pattern are signs of a natural environment
Shadow
Shadow – usually a visual obstacle for image interpretation
Gives height information about towers, tall buildings
Hobject
SShadow
tan HS
Tone
Band of EM spectrum recorded by RS system may be displayed in shades of grey ranging from black to white
Tone:- continuous grey scale varying from white to black It refers to relative brightness or colour of objects in
an image
Note:- Humans differentiate 40- 50 individual shades of grey RS image
Colour more convenient for the identification of object
details
Texture Characteristics placement & arrangement of
repetitions of tone or colour in an image Visual impression of roughness or smoothness of an
image region
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