Skip to main content

Geographic CRS (Coordinate Reference System)

In GIS, a Geographic CRS (Coordinate Reference System) is a system used to define and represent locations on the Earth's surface using latitude and longitude coordinates. It is based on the concept of a three-dimensional ellipsoidal or spherical model of the Earth.

A Geographic CRS provides a framework for accurately specifying the position of a point on the Earth's surface by assigning numerical values to latitude and longitude. Here's a brief explanation of the components and characteristics of a Geographic CRS:

1. Latitude: Latitude measures the distance north or south of the Earth's Equator. It is expressed in degrees, with values ranging from -90° at the South Pole to +90° at the North Pole. The Equator is defined as 0° latitude.

2. Longitude: Longitude measures the distance east or west of a reference meridian. The most commonly used reference meridian is the Prime Meridian, which passes through Greenwich, London, and is assigned a value of 0°. Longitude values range from -180° to +180°, with negative values representing locations west of the Prime Meridian and positive values representing locations east of it.

3. Ellipsoidal and Spherical Models: Geographic CRSs can be based on either an ellipsoidal or a spherical model of the Earth. The ellipsoidal model approximates the Earth's shape as an oblate spheroid, while the spherical model represents it as a perfect sphere. The choice of model depends on the level of accuracy required for a particular application.

4. Datum: A datum is a mathematical model that defines the size, shape, and orientation of the Earth, serving as the reference framework for a Geographic CRS. Different datums are used worldwide, such as the World Geodetic System 1984 (WGS84) and the North American Datum 1983 (NAD83). The datum defines the position of the coordinate origin (0,0) and the orientation of the coordinate axes within a Geographic CRS.

5. Angular Units: Geographic CRSs typically use angular units, such as degrees, minutes, and seconds (DMS) or decimal degrees (DD), to express latitude and longitude values.

Geographic CRSs are widely used for various applications in GIS, such as mapping, spatial analysis, and data integration. They provide a common reference system that allows spatial data from different sources to be accurately aligned and analyzed together. When working with Geographic CRSs, it's important to ensure that data is transformed or projected correctly when required to match the desired coordinate system and avoid distortions or errors.

Comments

Post a Comment

Popular posts from this blog

geostationary and sun-synchronous

Orbital characteristics of Remote sensing satellite geostationary and sun-synchronous  Orbits in Remote Sensing Orbit = the path a satellite follows around the Earth. The orbit determines what part of Earth the satellite can see , how often it revisits , and what applications it is good for . Remote sensing satellites mainly use two standard orbits : Geostationary Orbit (GEO) Sun-Synchronous Orbit (SSO)  Geostationary Satellites (GEO) Characteristics Altitude : ~35,786 km above the equator. Period : 24 hours → same as Earth's rotation. Orbit type : Circular, directly above the equator . Appears "stationary" over one fixed point on Earth. Concepts & Terminologies Geosynchronous = orbit period matches Earth's rotation (24h). Geostationary = special type of geosynchronous orbit directly above equator → looks fixed. Continuous coverage : Can monitor the same area all the time. Applications Weather...
Post a Comment
Read more

Disaster Management

1. Disaster Risk Analysis → Disaster Risk Reduction → Disaster Management Cycle Disaster Risk Analysis is the first step in managing disasters. It involves assessing potential hazards, identifying vulnerable populations, and estimating possible impacts. Once risks are identified, Disaster Risk Reduction (DRR) strategies come into play. DRR aims to reduce risk and enhance resilience through planning, infrastructure development, and policy enforcement. The Disaster Management Cycle then ensures a structured approach by dividing actions into pre-disaster, during-disaster, and post-disaster phases . Example Connection: Imagine a coastal city prone to cyclones: Risk Analysis identifies low-lying areas and weak infrastructure. Risk Reduction includes building seawalls, enforcing strict building codes, and training residents for emergency situations. The Disaster Management Cycle ensures ongoing preparedness, immediate response during a cyclone, and long-term recovery afterw...
Post a Comment
Read more

Disaster Risk

Disaster Risk 
Post a Comment
Read more

Evaluation and Characteristics of Himalayas

Time Period Event / Process Geological Evidence Key Terms & Concepts Late Precambrian – Palaeozoic (>541 Ma – ~250 Ma) India part of Gondwana , north bordered by Cimmerian Superterranes, separated from Eurasia by Paleo-Tethys Ocean . Pan-African granitic intrusions (~500 Ma), unconformity between Ordovician conglomerates & Cambrian sediments. Gondwana, Paleo-Tethys Ocean, Pan-African orogeny, unconformity, granitic intrusions, Cimmerian Superterranes. Early Carboniferous – Early Permian (~359 – 272 Ma) Rifting between India & Cimmerian Superterranes → Neotethys Ocean formation. Rift-related sediments, passive margin sequences. Rifting, Neotethys Ocean, passive continental margin. Norian (210 Ma) – Callovian (160–155 Ma) Gondwana split into East & West; India part of East Gondwana with Australia & Antarctica. Rift basins, oceanic crust formation. Continental breakup, East Gondwana, West Gondwana, oceanic crust. Early Cretaceous (130–125 Ma) India broke fr...
Post a Comment
Read more

Discrete Detectors and Scanning mirrors Across the track scanner Whisk broom scanner.

Multispectral Imaging Using Discrete Detectors and Scanning Mirrors (Across-Track Scanner or Whisk Broom Scanner) Multispectral Imaging:  This technique involves capturing images of the Earth's surface using multiple sensors that are sensitive to different wavelengths of electromagnetic radiation.  This allows for the identification of various features and materials based on their spectral signatures. Discrete Detectors:  These are individual sensors that are arranged in a linear or array configuration.  Each detector is responsible for measuring the radiation within a specific wavelength band. Scanning Mirrors:  These are optical components that are used to deflect the incoming radiation onto the discrete detectors.  By moving the mirrors,  the sensor can scan across the scene,  capturing data from different points. Across-Track Scanner or Whisk Broom Scanner:  This refers to the scanning mechanism where the mirror moves perpendicular to the direction of flight.  This allows for t...
Post a Comment
Read more