![]() The MTM projection, which is also called a 3-degree Transverse Mercator (3TM) projection, may be considered as a densification of the UTM projection. However, some zones (between 1 and 13) are modified by half a degree to avoid having a zone boundary to go through a city or town. The first MTM zone (Zone 1) has its central meridian at W53°, which crosses near St-John’s, Newfoundland. The narrower zones can fit better to the survey area, and therefore, the scale factor along the central meridian becomes 0.9999, resulting in less distortion when compared to UTM. The Modified Transverse Mercator (MTM) coordinate system is similar to UTM, but the zones are reduced to 3° of longitude (1.5° on each side of a central meridian). Concept of the Universal Transverse Mercator (UTM) projection. Canada is covered by sixteen UTM zones, numbered from 7 to 22.įigure 6. UTM is a conformal projection system because the scale factor is applied in all directions. ![]() The distortion due to the scale factor is less than 0.1%. The scale factor is less than 1 between them, reaching a minimum of 0.9996 at the central meridian, and larger than 1 outside them. The lines of true scale are approximately 180 km east and west of the central meridian. In both cases, the planar coordinates increase eastward and northward. In the southern hemisphere, the origin is the same intersection, but the pair (x, y) is now (500,000 m, 10,000,000 m) to avoid negative y coordinates. In the northern hemisphere, the intersection of the equator and the central meridian of the zone makes the origin where the pair (x, y) is (500,000 m, 0 m). The first zone (Zone 1) covers longitude 180° to 174° west of the Greenwich meridian zone numbering increases eastward. In this system, the Earth between latitudes of N84° and S80° is divided into 60 zones of 6° in longitude (3° on each side of a central meridian). The next two sections describe briefly these two projections.įigure 6 shows the concept of the Universal Transverse Mercator (UTM) coordinate system involving an imaginary secant cylinder intersecting a spherical Earth to define projection zones. For these reasons, Universal Transverse Mercator (UTM) and Modified Transverse Mercator (MTM) coordinates are commonly used in different fields of activities. In surveying and engineering, where many projects are conducted over small areas, it is generally simpler to work with planar coordinates, as systematic errors caused by the Earth’s curvature are negligible. Since the projection cannot be done without distortion, one must decide about the characteristic, which is intended to be shown accurately at the expense of others, or a compromise of several characteristics. Each type of projection has its own advantages and disadvantages, and the selection of one or another depends mainly on the needs of the user. They are based on mathematical formulas designed to project coordinates to a different but similar surface to achieve a particular purpose, such as preserving the scale, form or surface area of objects. Projections form a category of coordinate systems.
0 Comments
Leave a Reply. |