《周礼·地官司徒·大司徒》
用土圭测日影之法测量土地四方的远近，校正日影，以求得地中央的位置。
以土圭之法测土深，正日景，以求地中。
Use the method of measuring the length and shortness of the land with the sundial to measure the distance of the four sides of the land, correct the shadow of the sun, and seek the central position of the land.