Page | 18
Figure 17 shows that making the plane surface secant to the ellipsoid allows for a greater area to be covered with an equivalent scale distortion.
LINK
EPSG parameter database
1.3.2 Mapping Parameters A projection requires a set of parameters that are used to convert between latitude and longitude and easting and northing. These parameters can be found in the EPSG geodetic parameter database.
Figure 17: The plane surface can be tangent or secant to the ellipsoid. Secant permits the scale distortion to be distributed more evenly and therefore a larger area to be covered per unit distortion.
For a Transverse Mercator projection and a Lambert Conformal Conic projection these are respectively:
The geographic origin is the intersection of the central meridian with the latitude of the origin. The projection origin values at that point are the false easting and false northing. The reason for the high positive values for these parameters where applicable, is to avoid negative values. In both cases above this is for the easting but is not necessary fo h no h ngs wh ch bo h‘0’, s h p oj c on sno n nd dfo us souhof h o gn.
There are several other types of projection, most of which are of more interest to cartographers than having any application in E&P.
1.3.3 Distortions in Mapping We have already seen in the Geodesy section above, that by modelling the Geoid using an ellipsoid, we have already introduced some distortion in the way that the Earth is represented. Without adjustment, that distortion increases as we proceed further from the point of origin where the datum was established. However, with a well-established datum, these distortions can be minimized. When we make calculations from the E h’s su f c o fl (projection) surface, we introduce an additional set of distortions. These are in area, shape, scale and azimuth.
Made with FlippingBook flipbook maker