Talk:Georeference

From Wikipedia, the free encyclopedia
Jump to: navigation, search

"to define its existence in physical space." this is very very unclear.

why? —Preceding unsigned comment added by 139.153.176.222 (talk) 10:50, 25 June 2010 (UTC)

Concept in Georeferencing[edit]

1) What is Latitude & Longitude?
Latitude: is the angular distance, in degrees, minutes, and seconds of a point north or south of the Equator. Lines of latitude are often referred to as parallels. Longitude: is the angular distance, in degrees, minutes, and seconds, of a point east or west of the Prime (Greenwich) Meridian. Lines of longitude are often referred to as meridians.
2) What is Map?
Map is a graphical representation of earth surface or part of earth surface on paper using projection, scale,, legend, Sign and symbol.
3) What is map Scale?
Scale is the distance ratio between tow point on the map and corresponding point on ground. Representation of Scale
1.Ratio i.e. (1:50000)
2.Word/Statement i.e. (1cm=25 km)
3.Fraction i.e. (1/50,000)
4.Graphical
4) What is Projection?
Projection is a method of representation 3D earth surface feature on the 2D plane sheet using mathematical or geometric techniques. In Projection x-y Grid system is used to represent feature location and it’s bound.
5) What is Datum?
A geodetic datum is a reference from which measurements are made. In surveying and geodesy, a datum is a set of reference points on the Earth's surface against which position measurements are made, and (often) an associated model of the shape of the earth (reference ellipsoid) to define a geographic coordinate system. There are two types of datum A) Horizontal datum B) Vertical Datum
6) What is the difference between a projection and a datum?
A projection is the manner in which data that is collected from a spherical globe is translated to a flat surface like a LCD monitor. They are also referred to as coordinate systems. There are a large number of projections, the two most commons ones in the US are Universal Transverse Mercator (UTM) and State Plane. A geodetic datum (such as WGS84 and NAD83) is a geometric model of the size and shape of the earth and is used to guide the orientation and origin of the projection system. Taken together, the projection and datum determine the manner in which the pixels that make up your satellite imagery are arranged on the screen as well as the geographic information (i.e.latitude and longitude) that is tied to the data.
7) What is Georeferencing?
In GIS, georeferencing is the process of scaling, rotating, translating and assign graphical information to raster images with the help of projection or co-ordinate system and computerized tool, particularly raster images, to match the geographical coordinate system. An ordinary raster image is made up of pixels that have no particular size. By georeferencing, each individual pixel is given a particular coordinate corresponding to the point on the ground that it represents. Georeferenced images can be placed in layers on a GIS and used to locate positions on the ground.
8) What is the difference between georeferenced and orthorectified imagery?
The main difference is the horizontal accuracy of the imagery you will receive. For many applications, georeferenced (Standard) imagery will suffice. While this product has lower accuracy than does orthorectified imagery, it can be produced quicker and at a lower cost. The higher accuracy of orthorectified imagery is achieved by tying the data to a fine Digital Elevation Model (DEM) at photo-identifiable points (Ground Control Points or GCPs) with known latitude and longitude.
9) What is resampling and which method should I choose?
Resampling is another result of transforming an image of a spherical world for display on a flat surface. Resampling determines the spectral values that are assigned to each pixel of your satellite imagery. The method you should choose depends on your project needs and the product you order. If you are completing spectral analysis and/or classification, you should choose Nearest Neighbor resampling. For the majority of other users, either a Cubic Convolution or Pansharpening resampling method is recommended.
10) What is warping?
Warping means warps a raster based on the input control points using a polynomial transformation. This is similar to georeferencing using a text file. We specify the source and target coordinates. The transformation type (polynomial order) from which to choose is dependent on the number of control points entered. The DGN file is used as the projection for warping in Microstation .The re-sampling method is nearest neighborhood.
11) Control point
Control points means Points on the toposheet where world coordinates are explicitly known
12) Way-point
Points with world coordinates collected on field survey
(User talk:Parmeshwar Poul (GIS Analyst)) 07:01, 27 April 2011 (UTC)