拱坝是水利上一种先进坝型，尤以等厚圆拱的拱坝，设计与施工均较方便。我国中小型拱坝均采用这一坝型。等厚圆拱有定半径定中心角的，也有变半径变中心角的。后者具有一般性，对于它的放样计算，已介绍有弦线偏角法。该法原理虽简单，但仪器要上坝、量距测角手续较多，且经常与坝面施工发生干扰。另外，由于该法是采用前方交会原理定点的，各点点位误差不一。同时，在施工中，坝面一般不平整，对量距精度影响也较大。为了克服 Arch dam is an advanced water conservancy dam type, especially arch dam with equal thickness, design and construction are more convenient. Small and medium-sized arch dam in our country are using this type of dam. Equal thickness of a fixed radius of the center of the arch, but also change the center of the radius of the radius. The latter is general, and for its stakeout calculation, there is introduced a string angulation method. The principle of the law is simple, but the instrument to the dam, gage more measuring procedures, and often dam construction interference. In addition, as the law is the use of the principle of the intersection of the front of the fixed point, the bit error of each point. In the meantime, during the construction, the dam surface is generally not smooth, and the influence on the gauge precision is also large. In order to overcome