After dinner that day, all the soldiers gathered in the "collective dormitory" in the outer valley and followed Lin Feng to "go to night school".

The wooden beds in the middle of the quarters were all moved to the corners, and a large open space was made in the middle of the room, and all the soldiers sat on the floor.

At the front of the soldiers, Lin Feng held a short, smooth branch in his right hand and gently knocked it in his left hand. Behind him was a white piece of paper hanging on the wall, and on the table next to him was a pen, ink, paper, and inkstone. Not to mention, Lin Feng really felt a bit like a fake "Night Professor" at this time.

Lin Feng also coughed dryly, attracting the attention of all the soldiers to him, and said, "Have any of you ever heard of the Six-Body Cartography?" ”

The soldiers turned their heads back and forth and looked at each other, and they all shook their heads slightly, if they loved to read when they were young, I am afraid that few would be willing to come to be soldiers. After a while, Zhao Chengyu, a guard of King Zheng's Mansion who was aspiring to be a painter, raised his hand.

Lin Feng pointed at him.

Zhao Chengyu Shi Shiran stood up, flicked the wide military uniform on his body, and opened his mouth to say: "The six bodies of cartography refer to the six principles of drawing maps proposed by Pei Xiu in the Jin Dynasty, which are the score, the quasi-hope, and the Dao-" Speaking of this, Zhao Chengyu suddenly found that he had forgotten the content behind it, so he had to scratch his head in embarrassment. At this moment, the other soldiers all laughed together.

Lin Feng nodded and motioned for Zhao Chengyu to sit down.

Pei Xiu was born in 224 A.D. at the age of 47 and served as prime minister during the reign of Emperor Wu of the Jin Dynasty. According to "the six armies passed, the area is far and near, the mountains and rivers are dangerous and easy, and the journey is straight", with the help of the Menke Jingxiang, he compiled the earliest atlas of China - "Yugong Regional Map" and "Topographic Abbot Map". These maps, all up to one zhang square, are drawn according to the ratio of "one is divided into ten miles, and one inch is a hundred miles" (that is, 1:1,800,000). Undoubtedly, this is the most complete and detailed map of its time.

In the process of making these maps, Pei Xiu put forward the most scientific and perfect cartographic theory in the world at that time, the six bodies of cartography, which correctly clarified the relationship between map scale, orientation and distance, and had a profound impact on the map-making technology after the Western Jin Dynasty in China. It is precisely for this reason that Pei Xiu is known as the "father of scientific cartography in China".

According to records, the first of the six bodies of cartography is the "fraction", which is used to reflect the proportion of area, length and width, that is, the current scale; the second is "quasi-hope", which is used to determine the mutual orientation relationship between landforms and features; the third is "Daoli", which is used to determine the distance of the road between the two places; the fourth is "high and low", that is, the relative elevation; The fifth is "square evil", that is, the ups and downs of the ground slope; The sixth is "straight", that is, the conversion of the ups and downs of the field and the distance on the map. After him, the famous maps of ancient cartographers such as Jia Tan in the Tang Dynasty, Shen Kuo in the Song Dynasty, Zhu Siben in the Yuan Dynasty, and Luo Hongxian in the Ming Dynasty all inherited the principle of the Six Bodies of Cartography.

Lin Feng didn't continue Zhao Chengyu's words, and first told a small story: "Do you know the Tao but don't know the Tao, back then, after Liu Bang, the ancestor of the Han Dynasty, led the army to attack Xianyang, what was the first thing he did to his most important adviser, that is, Xiao He of the future Xiangguo?" He didn't take gold or silver, so he rushed into the official treasury and snatched all the maps of the world collected by Qin Shi Huang into his own hands to prevent the soldiers from being damaged in the slightest. It turned out that after Qin destroyed the Six Kingdoms, he had specially collected the maps of various countries in Xianyang, and kept them secret. What is this for? ”

Lin Feng looked in a circle at the soldiers in front of him, and saw that everyone showed curious looks, and then said, "That's because the two countries are at war, and military intelligence is important, and military intelligence is the first priority!" ”

Lin Feng tapped the short branch in his hand twice on the paper behind him, and said loudly: "Why do people laugh at those scholars who sit on paper in the room and talk about war? The reason is very simple, if you don't even know the actual situation of the battlefield, or even the geography of the mountains and rivers on the scene, but you are delusional about strategizing and winning thousands of miles away, isn't this nonsense? ”

Turning around, Lin Feng picked up the brush and wrote down six words on the paper, such as "Score, Quasi-Wang, Daoli, Superior, Fang Evil, and Straight", and then pointed to these words and said: "This is the six bodies of cartography." But to put it mildly, these words are not easy to understand, I will turn them into easy-to-use, easy-to-remember words, and everyone remembers the more key ones are 'far and near, azimuth relationship, height difference'. ”

Lin Feng wrote these words on the white paper again, pointed them one by one and said: "Far and near, that is, we see the size and proportion of mountains, rivers, roads and other objects, which are miniature on the map. As for the ratio of the two, here, I would like to ask everyone to follow the ancient example, in which the general picture is 'divided into ten miles, and one inch is a hundred miles', and the small map is 'one is divided into one mile, and one inch is ten miles'. ”

"Brother Lin, we are surrounded by mountains, how do you estimate the distance, is it in a straight line or the actual distance?" Zhang Yuewen raised his hand and asked.

"That's a good question, whether it's a mountain or a plain, I'll teach you a method of finger ranging." Lin Feng stretched out his right hand into a fist at shoulder level, gave a thumbs up, and then explained, "Close your left eye first, let your right eye, thumb, and target form a straight line; Then, close your right eye and open your left eye, where your left eye and thumb are on the right side of the target. At this time, visually measure the distance from the target at that point, multiplied by ten, which is the approximate distance you will have to the target. ”

The soldiers below did the same, and one of the soldiers sitting behind the most Lu said in surprise: "Lord Lin, the distance between me and you is about ten meters. ”

Hearing this, Lin Feng strode towards the soldier, and after nine steps, there was still a foot away, almost ten meters. Lin Feng immediately gave the soldier a thumbs up.

Seeing this scene, all the soldiers desperately kept their left and right eyes open back and forth, measuring everywhere. Ge Chang opened his mouth and asked, "Lord Lin, is this method accurate at a long distance?" ”

Lin Feng replied with a smile: "This method of finger ranging can generally estimate four to eight miles of road, of course, there is a premise for this, you must have obvious objects such as houses and trees in front of you. If you practice a lot every day, the error should be about 200 meters. ”

Then, Lin Feng pointed to the words "azimuth relationship", and then said: "The azimuth relationship is actually the mutual relationship between various objects, which is nothing more than the north, south, west, east of one object in the north, south, west, east and other directions of another object, plus the southwest, northwest, southeast, northeast and other directions, of course, if we invent more accurate instruments in the future, it will be accurate to the specific angle." ”

This involves the compass and protractor that Lin Feng plans to launch in the future, Lin Feng didn't say much, and then pointed to the words "high drop" and said: "For how to measure the height of an object, there has been a simple method since ancient times: immediate results. ”

Lin Feng took a waist knife and asked a soldier to hold it vertically on the table, and then asked a soldier to erect an inkstone at a distance from the table, and he picked up a candle and placed it on the side of the waist knife, signaling the two soldiers to draw a mark on the top of the waist knife and the shadow of the inkstone.

Lin Feng pointed to the marks of the two shadows and explained: "For example, this waist knife is a towering tree, and the inkstone is equivalent to a small object around us. ”

Speaking of this, Lin Feng saw that many soldiers were scrambling to raise their hands, smiled and pressed their hands down, and said loudly: "I know what you want to say, it is impossible to have the sun every day, and then there will be a shadow of the object, right?" Then I'll tell you a simple way. ”

Lin Feng made a gesture of finger ranging again, and continued: "Just now we learned the method of finger ranging, you measure the approximate distance to the top of the mountain and the distance to the foot of the mountain, subtract the two, and multiply it by its own number. For example, if you calculate that the distance between two is ten meters, then the height of the mountain should be ten times ten, which means that the mountain is one hundred meters high! ”

Here, Lin Feng used the most famous Pythagorean theorem, that is, the square of the hypotenuse of a right triangle is equal to the sum of the squares of the two straight sides, but he didn't want to complicate things yet, so naturally he wouldn't go into it in depth.

At this time, Ge Chang asked in confusion: "Lord Lin, what you said is very magical and useful, but why do we suddenly learn this?" ”

Lin Feng glanced at his legs, smiled mysteriously, and said, "You'll know tomorrow morning!" ”