Crystal projection method

Japanese: 結晶投影法 - けっしょうとうえいほう

The projection of three-dimensional features such as crystal faces and symmetric elements onto a flat surface. Stereographic projection is usually used. The crystal is enclosed in a sphere centered on the center of the crystal, and the intersection of a perpendicular line drawn from the center to the crystal face with the sphere is taken as the spherical projection of that face (called the pole of the face). For straight lines such as axes of symmetry, the intersection of the line with the sphere is taken as the spherical projection, and this sphere is then stereographically projected. The projection is drawn on a Wulff net, with the crystal faces indicated by their poles (points) and the symmetric elements indicated by their respective symbols. The face angles are determined by drawing a great circle passing through the two projected points and looking at the scale on the net. Edges and crystal zones are usually shown by projecting great circles perpendicular to them.

Source : Heibonsha Encyclopedia About MyPedia Information

Japanese:

結晶面や対称要素など立体的な特徴を平面上に投影すること。普通ステレオ投影法を用いる。結晶の中心を中心とする球で結晶を包み，中心から結晶面に立てた垂線と球面の交点をその面の球面投影（面の極という）とし，対称軸のような直線はそれ自身と球面との交点をその球面投影として，この球面をステレオ投影すればよい。投影図はウルフネットに描くが，結晶面はその極（点）で示し，対称要素はそれぞれの記号で示す。面角は二つの投影点を通る大円を描き，ネットの目盛から知る。また稜(りょう)や晶帯はそれに垂直な大円の投影で示すのが普通。

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