Official description from National Emblem and National Flag of the Republic of China Act (中華民國國徽國旗法):

Symbols

天, 地, 人, 和 = red field
天, 日, 月, 星 = blue rectangle
甲, 乙, 丙, 丁 = white sun
Ring between 甲, 乙, 丙, 丁 and 戊, 己, 庚, 辛 = blue ring
子, 丑, 寅, 卯, 辰, 巳, 午, 未, 申, 酉, 戌, 亥 = top angles of the 12 white rays
中 = center of the white sun
中, 甲 = radius of the white sun

Sizes/Radius

(Subparagraph 1, Article 4) 天地 : 天和 = 3:2
(Subparagraph 2, Article 4) 天日 = 天地/2
天星 = 天和/2
(Subparagraph 4, Article 4) 中甲 : 天日 = 1:8
(Subparagraph 5, Article 4) Applying following subparagraphs
(Subparagraph 3, Article 3) 中子 : 中甲 = 2:1
(Subparagraph 4, Article 3) 甲戊 = 甲丙/15
(Subparagraph 5, Article 3) Each angle of 子, 丑, 寅, 卯, 辰, 巳, 午, 未, 申, 酉, 戌, 亥 points = 30°, totaling 360°
(Subparagraph 6, Article 3) angle 子 towards north
angle 午 towards south
angle 卯 towards east
angle 酉 towards west

Description of Geometric Drawing

1. From 和 point draw a horizontal line with 人 point, and a vertical line with 天 point. Make lengths between 和–人 line and 和–天 line being aspect ratio of 3:2. From 人 point to draw a 人–地 line parallel to the 和–天 line. From 天 point to draw a 天–地 line parallel to 和–人 line, forming the 天地人和 red field.
2. Equally divide 和–天 line equally in 星 point, and divide 天–地 line equally in 日 point, forming the 天日月星 blue rectangle.
3. Equally divide 天–星 line horizontally and 天–日 line vertically, forming the crossing point 中. On the 天–日 line, take a 中–甲 line, make its length equivalent to 1/8 of 天–日 line. Use the 中 point as the center of the circle and 中, 甲 as the radius to draw 甲乙丙丁 circle, forming the white sun.
4. For geometric drawing of the blue circle and the 12 rays, see the description of geometric drawing for the national emblem for details.