Tianjin MengMeng photography

(1) Isometric projection, also known as conformal projection, means that the included angle between any two directions on the projection plane is equal to the corresponding angle on the ground. In a small range, the graphics on the map can remain similar to the field; Can't make its corresponding area keep a constant proportion; The local scale of any point on the map in all directions should be equal; The local scale of different places changes with the change of latitude and longitude.

(2) Equal (surface) product projection is a projection method that any graphic area on the map is enlarged by main scale and keeps the same size as the corresponding graphic area on the ground. Equal-product projection, on the other hand, cannot keep equal angles at the same time by keeping equal products.

(3) Arbitrary projection. Arbitrary projection is a projection with neither equal angle nor unequal product, and there is also an "isometric projection", which has no length deformation on the standard latitude and longitude lines and is mostly used for teaching drawing in primary and secondary schools.

2. Classify according to the shapes of warp and weft projected on the positive axis.

A> geometric projection (using the perspective relationship, the latitude and longitude network of the earth's surface is projected onto a plane or a geometric surface such as a cylindrical surface or a conical surface that can stand on a plane. ) is divided into the following three types:

(1) plane projection, also known as azimuth projection, is a projection method that projects the longitude and latitude lines of the earth's surface onto a plane tangent to the spherical surface. Plane projection is mostly perspective projection, that is, taking a certain point as the viewpoint, the image on the spherical surface is directly projected onto the projection plane.

(2) Cone projection, in which a cone surface is tangent or tangent to the latitude circle of the ground, and the axis of the cone coincides with the axis of the ground, and then the longitude and latitude lines on the ground are projected onto the cone surface from the viewpoint of the spherical center, and then cut into a plane along the cone mother line. Nature: On the map, the latitude is concentric arc, and the longitude is a straight line intersecting with the ends of the earth.

(3) Cylindrical projection: a cylinder is sleeved on the earth, and the axis of the cylinder passes through the center of the sphere, so that the longitude and latitude lines on the ground are evenly projected onto the cylinder, and then flattened along the bus line of the cylinder to form a cylindrical projection network.

(4) Multi-cone projection: In the projection, the weft is a coaxial arc, and the meridian is a curve with a symmetrical center diameter line.

B> conditional projection (non-geometric projection) (1) Pseudo-azimuth projection, in the case of positive axis, the latitude of Pseudo-azimuth projection is still projected as concentric circles, except that the central meridian is projected as a straight line, other meridians are projected as curves that are symmetrical with the central meridian and intersect with the common center of latitude.

(2) Pseudo-cylindrical projection, on the basis of cylindrical projection, it is stipulated that the latitude is still a concentric arc, and all other meridians are projected as curves symmetrical to the central meridian except that the central meridian is still a straight line.

(3) Pseudo-conic projection, in which the latitude is a concentric arc and the longitude is a curve intersecting the center of the circle.

3. Classification according to the relative position between the projection plane and the earth's surface (the relationship between the projection axis and the earth's axis)

(1) Orthographic projection (coincidence): the center line of the projection plane is consistent with the earth axis.

(2) Oblique axis projection (oblique): the center line of the projection plane is inclined with the earth axis.

(3) Horizontal axis projection (vertical): the center line of the projection plane is vertical to the earth axis.

4. According to the relationship between the projection plane and the earth's surface in geometric projection.

(1) Tangent Projection

(2) Cutting projection

5, the application of projection

(1) Conical projection: It is mainly used in countries and regions with mid-latitude along the east-west extension.

(2) Cylindrical projection: it is a special case of conical projection, and the cylindrical projection of the positive axis shows mutually orthogonal straight lines. Equiangular cylindrical projection (Mercator) has the characteristics that the equiangular route is straight, which is most suitable for compiling various nautical and aviation charts.

(3) Azimuth projection: Isomorphic lines are concentric circles, which are most suitable for representing areas with circular outlines, such as maps representing polar regions.