Showing posts from March, 2020

Georeferencing Using QGIS

Georeferencing of ToposheetIntroductionGeoreferencing is a process of establishing a mathematical relationship between the image coordinate system and the real world spatial coordinate system.Georeferencing an important process of spatial data including both raster and vector data. By this process of georeference, different measurement based analysis such as distance and area as well as locating object on ground can be possible on both type of spatial data
These georeferenced data can be used for mapping and change detection analysis also for measurement distances between two given point/locations. This is possible only because of georeferencing otherwise un-georeferenced data will treat as image in which only features can be visualized and no measurements can be done.
Georeferencing is primary steps in remote sensing process for spatial data and all GIS and image processing software can be used for georeferencing.  To georeference a satellite image one need to use Ground Control Point…

Digital Image Processing Tutorial-Image Interpretation Part-III

Image Interpretation ElementsAs discussed in last article about image interpretation and also defined image interpretation elements/keys.
Elements/Keys are below-
Figure-Use of Elements/Keys for Image Interpretation SizeShapeShadowTone/ColorTexturePatternHeight & depthSiteAssociationColorColor is primary element and convenient to identify and recognize earth surface feature on multi band satellite image. Color images can be obtained by combination of three bands and two type of combinations can be prepared, first Natural Color composite (NCC) and the second one is False color composite(FCC). In both type of combination color may vary for the same feature, such as vegetation appears green in NCC whereas it will appear red in FCC.
Figure- Color variation in FCC and NCC ToneIt refers to the average brightness of an area or, in the case of color imagery, to the dominant color of the region. It depends on the nature of the surface and illumination. Smooth surfaces behave like specular refle…

Digital Image Processing Tutorial-Image Interpretation Part-II

Image interpretation The main objective of image interpretation is to create information in the form of thematic maps. A thematic map can be prepared by categorizing all pixels of the image into classes or themes to generate map from the remote sensing data. One can take different theme based on field of study, for example one can create Land use/land cover map based on mapping different categories such as water, forest, range land, urban etc.Mapping and quantification of surface water bodies/ water resources.Geological map based on identification of landforms, rock types, folds, faults and fractures.Urban change detection maps using multi dateremote sensing data.
Below steps followed for Image Interpretation-
Classification                Assign objects to classes
               Detection, recognition, identification.                Interpreter confidence is ranked as possible, probable
Measurement               Uses image scale to derive measurements such as length with distance and volume