Geodesy and Geodetic Datum Overview

A geodetic datum is a reference system that defines a coordinate system to approximate the Earth's shape, enabling accurate positioning and measurements on its curved surface.

The geoid is always perpendicular to gravity and coincides with the sea surface, meaning that the sea surface acts as a reference for measuring elevation.

The ellipsoid is a mathematically perfect shape used for mapping and calculations. The geoid is the true shape of the Earth, which includes irregularities caused by mountains, valleys, and variations in gravitational pull.

<p>The World Geodetic System 84 (WGS84) is the current international standard ellipsoid used to represent the Earth's shape and size for precise positioning.</p> Signup and view all the answers

<p>Meridians are lines of longitude that measure the distance east or west from the Prime Meridian, with distances equal at the equator but converging at the poles.</p> Signup and view all the answers

<p>Latitude measures the distance north or south of the equator and is parallel, meaning the distance between latitudes is constant regardless of longitude.</p> Signup and view all the answers

<p>The geoid reflects the Earth's true shape, incorporating irregularities from mountains, valleys, and variations in gravitational pull.</p> Signup and view all the answers

<p>Elevation is based on the distance from the geoid because the geoid provides a consistent and accurate reference level that accounts for variations in land surface.</p> Signup and view all the answers

<p>Map projections allow the representation of Earth's curved surface on flat maps for navigation and analysis, despite inevitable distortions.</p> Signup and view all the answers

<p>Cylindrical normal projections touch the Earth along the equator, while cylindrical transversal projections can be rotated to touch the Earth along any meridian.</p> Signup and view all the answers

<p>Secant projection models reduce distortion by allowing the projection paper to cut through the Earth's surface at two lines instead of just touching it.</p> Signup and view all the answers

<p>UTM divides the world into 60 zones for accurate mapping, centered on lines of longitude, significantly reducing distortion for localized maps.</p> Signup and view all the answers

<p>RT90 is an older system developed in 1990 based on a different ellipsoid, while SWEREF 99 TM is a modern system, introduced in 2000, that uses the WGS 84 ellipsoid for better global compatibility.</p> Signup and view all the answers

<p>SWEREF 99 TM was adopted due to its better accuracy and compatibility with global GPS systems compared to the older RT90 system.</p> Signup and view all the answers

<p>A graticule is the distorted grid of longitudes and latitudes projected onto a flat surface representing the Earth's curvature.</p> Signup and view all the answers

<p>The central meridian for both RT90 and SWEREF 99 TM is at 15° east longitude, which serves as a reference point for coordinate systems in Sweden.</p> Signup and view all the answers

<p>Cylindrical transversal projections are best used for mapping regions located in extreme north or south due to their flexible orientation along meridians.</p> Signup and view all the answers

<p>It allows for a full 360° coverage of the Earth, establishing east and west directions from the Prime Meridian.</p> Signup and view all the answers

<p>A nautical mile is approximately 1852 meters and is defined as one minute of arc along a meridian, varying in real distance with latitude.</p> Signup and view all the answers

<p>The elliptical shape causes variations in geoid height, making some national datums necessary for accurate local measurements.</p> Signup and view all the answers

<p>Geoid height is the difference between the geoid and the ellipsoid, crucial for accurate surveying and GPS measurements.</p> Signup and view all the answers

<p>Local ellipsoids are tailored for specific regions, aligning closely with the geoid, while global ellipsoids serve a worldwide purpose.</p> Signup and view all the answers

<p>Scale distortion occurs when areas or distances on a map do not accurately represent their real-world sizes.</p> Signup and view all the answers

<p>Conformal projections preserve angles and shapes accurately, making them useful for local maps and navigation.</p> Signup and view all the answers

<p>Direction can become distorted, as no projection can preserve both scale and direction simultaneously.</p> Signup and view all the answers

<p>Latitude is measured as the angle between the equator plane and a line perpendicular to the surface at a given point.</p> Signup and view all the answers

<p>The equatorial radius is larger than the polar radius due to the Earth's slight oblateness, causing it to be flattened at the poles.</p> Signup and view all the answers

<p>EGM 96 measures variations between the geoid and the WGS84 surface, aiding in understanding Earth's gravity field.</p> Signup and view all the answers

<p>Direction-invariant projections preserve angles but may distort area, ensuring accurate directional representation.</p> Signup and view all the answers

<p>Projections use mathematical formulas to transform latitude and longitude values into x (easting) and y (northing) coordinates.</p> Signup and view all the answers

<p>WGS84 provides a consistent framework for positioning worldwide, despite local variations in geoid height.</p> Signup and view all the answers