Classification of map projections
The classification of map projections are usually based on three principles:
• the kind of normal main grid coordinate system ( by type of auxiliary geometric surface).
• the normal position of the pole of the coordinate system
• the nature of distortion.
Classification by type of normal grid.
The cylindrical:The simplest option projection. In this model, the plane maps by touching the globe at the equator , it wraps to form a cylinder. Meridians and parallels are projected on a plane, thus forming an orthogonal grid . This model is especially good for the image of the equatorial regions. In other regions, can be used cross- variant projection.
These projections meridians normal grids are depicted by parallel lines , perpendicular to the parallels . Generally used for image areas located along the equator or any parallels
The Conical: the construction of these projections the Earth's surface is transferred onto the lateral surface of the cone , which is then " cut " by one of the generators and deploying the plane. Conical projection is obtained by unfolding the plane of the cone , the covering earth. In its simplest and most frequently used version of the vertex of the cone is located on the line joining the poles of the Earth, and depicts the circumpolar region . From the top of equal angles out meridians and parallels form concentric circles around it. The cone touches the surface of the earth by 1-2 standard parallels. This form is often used for the image of the middle latitudes .
The Azimuthal: Here is the card plane tangent to the surface of the Earth.
Depending on the position of the center of the design relative to the plane of the azimuthal projections are divided into
central -a view located in the center of the globe,
stereographic - the point of view removed from the plane of the sky at a distance equal to the diameter of the globe,
orthographic - Access point of view is removed from the picture plane to infinity,
external - pt of view is out of the globe at a finite distance .
Of all azimuthal projections in their navigation are mainly used in the central and polar stereographic .
Imagine an infinitely remote light source on the opposite side , translucent globe and cast shadows of meridians and parallels the plane card.
These projections parallels the normal grid - concentric circles , and meridians - the radii of the circles . The angles between the meridians are equal to the corresponding difference in longitude .
For polar regions used stereographic projection.
The classification of the projections on the pole position .
• direct (normal) projection - when the zenith (Z) coincides with the geographic pole (PN) or projection in which the axis of the auxiliary surface coincides with the axis of rotation of the globe, and geographic meridians and parallels create a normal grid .
• lateral projection - if the zenith (Z) is located at the geographic equator , the axis perpendicular to the supporting surface of the axis of rotation of the earth.
• oblique projection - in which the axis of the auxiliary geometric surface makes with the axis of the globe acute angle .
Дата добавления: 2015-06-10; просмотров: 683;