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How are datums, projections, and coordinate systems used?
Without geodesy… The ability to accurately determine locations on the surface of the Earth is fundamental to GIS and GPS, and this is accomplished by using various datums, map projections, and coordinate systems. When working with the Land Mapper, or any geographic data, it is essential to have a basic understanding of these concepts.
How are X and Y expressed in a coordinate system?
X and Y refer to locations within a Cartesian coordinate system, where X identifies a position along the horizontal (X) axis and Y identifies a position along the vertical (Y) axis. •In a geographic coordinate system, longitude is expressed by the X value, and latitude is expressed by the Y value.
How is the position of the ellipsoid related to the datum?
The position of the ellipsoid with respect to the center of the Earth (indicated by the eccentricity) also varies among datums. The Clarke 1866 and GRS 1980 ellipsoids are positioned such that the surface of the ellipsoid better matches the North American continent.
Which is the best description of a coordinate system?
A coordinate system is a way to describe positions on the surface of the Earth. The coordinates of a point can be expressed in several ways – as latitude and longitude, or as meters or feet. Latitude and longitude coordinates are used to express points within a geographic coordinate system, such as NAD27 or WGS84.
Why do you need to know what datum your data is in?
The reason why this matters is because if you don’t know what datum your data is in, you or someone else will have to guess which datum the data are in, and this greatly increases the probability of positional errors when you import your data into the Land Mapper or GIS. Map Projection – What is it?
When do you report the datum for lat / long coordinates?
When noting lat/long coordinates or giving lat/long coordinates to someone, you must always report the datum which is used by the coordinates. Without the datum information, the user will have to guess which datum your lat/long coordinates are in, and this often leads to misalignment of features.
When do you need to use a coordinate system?
In some documentation external to SPICE, this is called a “coordinate frame.” A coordinate systemspecifies a mechanism for locating points within a reference frame. When producing or using state (position and velocity) or orientation (pointing) data, one needs to understand both the reference frame and the coordinate system being used.