awaken

Only if you open the empty ， you can actually know where the three dan tian is. Before that goal, the only feeling is Yang Chi come and down, circle around you body outside. Most of people can not distinguish where Dan tian is , because they don't have open the channel of Kundalini. If your channel of Kundalini is blocked, you won't have any feeling of dan tian. The only way to open the channel is 無為法Wuwei. It means that You can not DO anything to open it. What you can do is to follow.

丹田s are very different from 玄關。 丹田s have precise locations in body. But 玄關 is not. It only show up because of a special state. Sometimes we can see special lights inside 玄關。 People have different opinions about 下丹田。 Someone think it is lower than the navel ,but someone think it's in back of the navel ,not lower . If we concentrate our mind on the breath, we will feel some warm feeling under the navel. But if we can have a kind of pulse , which is different from blood pulse, we can know 下丹田 is in back of the navel. The chi of the pulse will be absorbed by the middle dan tian.

莊子謂大道不稱，大辯不言。蓋以道本無名，有何可稱？道本無形，有何可言？稱且不可，言且不可，更何可辯？然世有稱道者，有言道者。一自有稱，則是非混雜，而道不真矣；一自有言，則邪正相爭，而道有假矣。稱道不真，言道有假，不是稱道，反是謗道；不是言道，反是埋道。謗道埋道，塞修真之門，阻行道之路，為害最大，此予不得不強辨，以破其稱之不真；不得不細辨，以劈其言之有假。辨不真之稱，則不可稱之道，學者可不難於漸悟；辨有假之言，則不可言之道，學者可不難於默會。難悟者能使自悟，難會者能使自會，此前後辨難之存心也。雖然，既有辨矣，謂之無言可乎？既有言矣，謂之無稱可乎？既有稱矣，既有言矣，猶辨不真之稱、有假之言可乎？人亦稱矣，我亦稱矣；人亦言矣，我亦言矣；焉知人之稱者真乎，我之稱者不真乎？焉知我之稱者真乎，人之稱者不真乎？焉知人之言者假乎，我之言者不假乎？焉知我之言者假乎，人之言者不假乎？誰真誰不真，誰假誰不假，是在不稱道、不言道者見而自知之，吾烏乎辨？悟元子再序。

紫清翁云：其精不是交感精，乃是玉皇口中涎；其氣即非呼吸氣，乃知卻是太素煙；其神即非思慮神，可與元始相比肩。是即所謂元精、元氣、元神也。精氣神而曰元，是本來之物。人未有此身，先有此物。即有此物，而後無形生形，無質生質，乃從父母未交之時而來者。方交之時，父精未施，母血未包，情合意投，其中杳冥有物，隔礙潛通，混而為一，氤氳不散；既而精洩血受，精血相融，包此一點之真，變化成形，已有精氣神寓於形內。雖名為三，其實是一。一者混元之義，三者分靈之謂。一是體，三是用。蓋混元之體，純一不雜為精，融通血脈為氣，虛靈活動為神。三而一，一而三。所謂上藥三品者用也，所謂具足圓成者體也。不得言三，亦不得言一。學人多不知三而是一，一而是三，或抱元守一而落於著空，或煉藥三品而失於執相。著空執象皆非還元妙理。還元者，即還元精、元氣、元神也。若欲修道，先要知的此三物在混元中潛藏。離乎混元，便非先天精氣神本體。失卻本體，不是元物。心印經曰：上藥三品，神與氣精。恍恍惚惚，杳杳冥冥，視之不見，聽之不聞。從無守有，頃刻而成。曰恍惚、曰杳冥、曰有無，則為無形之物可知。惟此元精如珠如露，純粹不雜，滋潤百骸；元氣如煙如霧，貫穿百脈；元神至靈至聖，主宰萬事。知之可以延年益壽，長生不老。學者若能識得此三藥，則修道有望。

Sorry, I can't find the answer . But it's still worth of reading the book. http://www.academia.edu/6581869/Discriminations_in_Cultivating_the_Tao_Liu_Yiming_1734_1821_and_His_Xiuzhen_houbian

In 丹books, there are three 丹田，up上丹田，middle中丹田，down下丹田。 丹田 is where 丹 come from. There are many kinds of 丹。 烏肝black liver, 兔髓rabbit marrow and 黍米 millet And real 丹 - 金丹golden dan 上丹田，inside the head 中丹田，in the middle of the chest 下丹田，in the belly 丹田 is the center of energy Three centers

Liu Yiming (1734–1821) was one of the main representatives of Taoist Internal Alchemy, or Neidan. He was an 11th-generation master of one of the northern branches of the Longmen 龍門 (Dragon Gate) lineage, and the author of a large number of works that illustrate his views on both Taoism and Neidan. Liu Yiming was born in 1734 in Quwo, Pingyang 平陽 (in present-day Linfen, Shanxi). Before he reached the age of 20, he was severely ill three times (Sun Yongle 2011:302). After recovery, he began to travel, and in 1753 or 1754 he met his first master, whom he calls the Kangu Laoren 龕谷老人 (Old Man of the Kangu Valley). In 1757, he stayed in Beijing, where he studied ophthalmology following his father’s wish. Five years later, he moved to Henan, where he lived until 1765 working as a doctor (Sun Yongle 2011:302). In 1766 he resumed traveling, and around 1768 he met the Xianliu zhangren 遇仙留丈 (Great Man Who Rests in Immortality), who became his main master. The Xianliu zhangren (himself an earlier disciple of the Kangu laoren) gave Liu Yiming teachings on Neidan. As Liu Yiming reports in one of his works, it was under the Xianliu zhangren that he obtained the full awakening (Liu Yiming 2013:34; Baldrian-Hussein 2008:691). After the death of his father in 1769, Liu Yiming—who was then in his mid-30s—alternated periods of traveling (in Shaanxi, Gansu, Ningxia, and elsewhere) and of seclusion for a decade. In 1779 or 1780, he visited the Qiyun 棲雲 mountains in Jincheng 金城 (present-day Yuzhong, Gansu) and settled there to practice self-cultivation. From that time, this mountain became his stable residence, even though he occasionally traveled elsewhere. His abode, called Zizai wo 自在窩 (Nest of Being by Oneself), is still extant in the present day (Sun Yongle 2011:304; Baldrian-Hussein 2008:691). Liu Yiming devoted the second half of his life to teaching and writing. His biographies also report that he used his financial resources to restore temples, shrines, and other buildings; to buy and lease fields to poor farmers; and to provide burial ground to those who could not afford it. In 1816, he prognosticated an auspicious place for his tomb on top of the Qiyun mountains, and his “tomb cave” was built there. In 1821, on the 6th day of the 1st lunar month, Liu Yiming entered the cave, pronounced his final words to his disciples, and died (Sun Yongle 2011:8).