Many times, raster image data is supplied in a “raw” state and contains geometric errors. Whenever accurate area, direction, and distance measurements are required, raw image data must usually be processed to remove geometric errors and/or rectify the image to a real world coordinate system.
• Registration is the process of geometrically aligning images to allow them to be superimposed or overlaid.
• Rectification is the process of geometrically correcting raster images so they correspond to real world map projections and coordinate systems (such as Latitude/Longitude or Eastings/Northings).
• Orthorectification is a more accurate method of rectification because it takes into account terrain and sensor (camera) calibration details. Advanced orthorectification also uses platform position information.
A ground control point (GCP) is a point on the earth’s surface where both image coordinates (measured in rows and columns) and map coordinates (measured in degrees of latitude and longitude, meters, or feet) can be identified. Rectification is the process of using GCPs to transform the geometry of an image so that each pixel corresponds to a position in a real world coordinate system (such as Latitude/Longitude or Eastings/Northings). This process is sometimes called “warping” or “rubbersheeting” because the image data are stretched or compressed as needed to align with a real world map grid or coordinate system.
Geocoding in GIS
Geocoding is the process of finding associated geographic coordinates (often expressed as latitude and longitude) from other geographic data, such as street addresses, or zip codes (postal codes). With geographic coordinates the features can be mapped and entered into Geographic Information Systems.
A simple method of geocoding is address interpolation. This method makes use of data from a street geographic information system where the street network is already mapped within the geographic coordinate space. Each street segment is attributed with address ranges (e.g. house numbers from one segment to the next). Geocoding takes an address, matches it to a street and specific segment (such as a block, in towns that use the “block” convention). Geocoding then interpolates the position of the address, within the range along the segment.
Example: Let’s say that this segment (with + symbol) Jalan Anggrek Komp. Sukamenak Indah Blok E No.7, Bandung. You must give correct information about this address and its location in this segment. Such as id, street address, no, block, zip code, owner, and its relationship.
Geocoded locations are useful in many GIS analysis and cartography tasks. Geocoding is common on the web, for services like finding driving directions to or from some address, or finding a list of the geographically nearest store or service locations. Do you know GPS application in Nokia cell phone or Google Earth?