This TreePlotter™ tutorial provides general information on the coordinate reference system and constituent components used by the software to generate a map to plot assets.
Topics covered in this Tutorial:
- Coordinate Reference System
- Datums
- Coordinate Systems
- Projected Coordinate Systems
- Eastings and Northings
- British Standard 5837
Coordinate Reference System:
Coordinate reference systems are used to precisely define a spatial location using a coordinate system which allows for the exchange of unambiguous location data. A spatial reference system is comprised of a multitude of components including: datum (framework for measuring geographic coordinates through the use of latitude and longitude), a coordinate system (an area of measurable space with a defined unit of measurement like feet or meters, an origin, and axis vectors emanating from the origin), and a defined map projection (which converts the latitude/longitude coordinates into cartesian coordinates).
The best way to represent the curvature of the Earth is through the use an Ellipsoid/Spheroid, which expressed graphically, is a slightly squashed sphere. This representation contains two axes: a semi-major (which is aligned with the Equator and describes the distance from the equator to the center of the Earth) and semi-minor axis (which is aligned with the North Pole and describes the distance between the north Pole and the center of the Earth). This representation of Earth is referred to as a datum,
Datum
A datum is an abstract reference frame for determining precise locations on Earth through the use of coordinates. To provide context to the reference system, horizontal datums (longitude and latitude) can be used to define specific points on a map. TreePlotter uses the World Geodetic System 1984 (i.e. WGS84) ensemble datum which provides referencing across the world using a geocentric coordinate system.
Coordinate Systems
There are four main types of coordinate systems that form the basis for the thousands of coordinate systems that are in use: geographic which determines locations using spherical coordinates (latitude and longitude); geocentric which determines locations based on the center of mass of the Earth; projected which determines locations from an arbitrary origin point representing the Earth on a planar surface, and engineering. The WGS84 datum that TreePlotter utilizes is based on a geocentric coordinate system which means that locations are represented by coordinates (X, Y, Z) from Earth’s center of mass.
Projected Coordinate System
Maps use a projected coordinate system to represent spatial locations on a two dimensional surface using Cartesian (x, y) coordinates which, in some projections, may be referred to as eastings and northings. Each projected coordinate system is based on a particular map projection which creates a planar, or flat, map view from that of Earth’s curved surface. The projected coordinate system is the lens through which each map is viewed. Together with the datum, the grid system is established for determining location information. Common projection systems include worldwide projections like Universal Transverse Mercator (UTM) and Military Grid Reference System, and national systems like the United States National Grid and the British National Grid. TreePlotter uses the European Petroleum Survey Group (EPSG) 3857 projection (often written as EPSG:3857) using easting and northing axes, east and north orientations, and meters for unit of measurement.
Easting-Northing:
All map projections contain a natural origin, the location where projection coordinates intersect at the coordinate (0,0). Spherical coordinates, like latitude and longitude, use positive and negative values for coordinate locations. However, projections that use Easting-Northing values select a region within a rectangular grid with an established false origin. A false origin ensures all coordinate values remain positive because all values within the grid are east and north of the false origin.
British Standard 5837
The BS 5837 is a British standard that provides tree care recommendations for operations during the design, demolition, and construction processes of the urban environment. The Standard contains guidelines pertaining to the following areas of interest: site surveys (topographical survey, tree inventory, soil assessment, root protection area [RPA]), conception and design of structures around trees (constraints posed by existing trees, impact assessment, tree protection plan), technical design (tree protection zone barriers and site monitoring), demolition and construction (avoiding tree root damage, work with the RPA, subterranean construction), and site works and landscape operations drainage, topsoil quality, soil compaction, mulch, impervious surfaces, herbicides).
TreePlotter™ INVENTORY has developed an add-on module or UK-based customers to maintain compliance with the BS5837 such that a User can conduct a survey in accordance with the Standard guidelines. This module allows for mapping tree canopies, root protection areas, import/export CAD files and more.
Known Limitations:
- If you have data with tree coordinates in eastings and northings (most likely our UK customers), they will need to be given a coordinate system before uploading them.