What are the stories of Emperor Taizong's designation of Jiuyi Mountain as the location of the mausoleum?

When Emperor Taizong proclaimed himself emperor, he asked Feng Shui magicians Li and Yuan Tiangang to travel separately and choose a place for themselves to live in a hundred years. After receiving the order, the two met at the North-South Branch. Li went north and arrived in Liquan, Shaanxi Province, and found Jiuyi Mountain soaring into the sky, showing the domineering spirit of the king. So Jae-Il Lee found an acupoint in the middle of a ridge, buried a copper coin as a symbol, and left. And Yuan Tiangang, to the south, arrived at Liquan. He also thinks that Jiuyi Mountain is a treasure trove of geomantic omen, so he puts a silver needle where he thinks it is satisfactory. After returning to Beijing, they reported back to the palace together. Li Shimin, Emperor Taizong, was surprised to hear that both of them had chosen Jiuzhang Mountain, so he went to check with them. It turned out that Yuan Tiangang's silver needle was inserted from the copper hole buried by Li. Li Shimin was very surprised, so he decided to use Jiukunshan as the location of the mausoleum.