What is the principle of keyhole imaging?

A: pinhole imaging is formed by the linear propagation of light

Lost in the wild how to do? Use the watch to identify the direction, very practical!
Divide the time by 2, and the scale of the number is aligned with the direction of the sun, then the direction of the 12 o'clock scale is the north. For example, 2 p.m. is 14 o'clock, divide by 2 to get 7, and the position of 7 o'clock is aligned with the direction of the sun, then the direction of 12 o'clock is the north

Great! I've always wanted to buy a compass

How to use watch to judge direction
If you know this, you should not be afraid of getting lost

Use the sun and the watch to judge the direction: in the daytime, if you are wearing a watch, you can use the watch and the sun to judge the direction. Put the watch flat so that the hour hand is facing the sunlight (the direction of light or the opposite direction of human shadow), and then divide the angle between the hour hand and the 12 o'clock on the watch equally, The direction of this bisector is South (this method is applicable to the area north of Tropic of cancer and close to Beijing time zone)
So, what is the principle of this method?
In the area to the north of Tropic of cancer, at 12:00 local time, the sun is in the south, and the sun moves about 15 degrees westward every hour. In this way, the angle of the sun from the South can be calculated according to the time at that time, and then the South can be measured by using a watch as a protractor (the interval of one hour on the watch is 30 degrees), Due south is the direction of 30 degrees clockwise for the sun at 10 o'clock, and the time after 12 o'clock (afternoon) is counter clockwise. The corresponding angle is due south. Note that the time here must be local time, or the time used is close to local time
More about using the sun and watch to judge the direction:
[ZhiBei method]
Watch flat, half of the local time to the sun, 12 o'clock position for the north
[principle] local time 0:00 is due north, the sun turns one circle, the watch turns two circles, the watch time divided by 2, is exactly where the sun is
[guide method]
Watch flat, with the hour hand pointing to the sun, then the hour hand and the bisector of 12 o'clock point to the south
[principle] local time 12:00 is due south. When it is less than 12:00 or more than 12:00, the angle of the hour hand from 12:00 is twice of the actual angle of the sun from noon
One day at 16 o'clock
North pointing: point 8 o'clock to the sun and 12 o'clock to the north
Guide method: point to the sun at 16 o'clock and South at 14 o'clock
Note: as for the guide method, the guide method should be used between 6:00 and 18:00 in local time. For example, when you see the sun at 3:00 in local time, point to the sun at 3:00 with the hand, and the bisector of the angle between 3:00 and 12:00 points to the north
As for the example of North pointing, at 12 noon, point 6 to the sun, and 12 to the north; at 16 PM, point 8 to the sun, and 12 to the north. At 0 o'clock, 12 to the current position of the sun, that is, the midnight meridian. This method can also be used in the polar daytime (except the poles)
On the problem of error: this principle itself is not wrong, the error is because we did not consider the difference between local time and Beijing time when looking at the table. Calculate the time difference according to the longitude difference between the local longitude and the 120 longitude of Beijing time, and then subtract the local longitude from the East and West. Then we can use the above method to judge the correct direction
For example: a place is 35 ° n, 110 ° e, and the watch is 12 o'clock Beijing time. When judging the direction, we should first calculate that the local time is 12 o'clock - (120 ° - 110 °) × 4 minutes / degree = 11:20, and then use half of the time of 11:20, that is, the position of 5:40 to face the sun at the moment, so the direction of 12 o'clock on the dial is of course more accurate
The above information source network, hope to help you

How to distinguish direction with watch?
Several discrimination methods are said!

There are two ways to know: 1. When the watch is placed horizontally, the hour hand points to the sun, and the middle line between the hour hand and the 12 o'clock scale points to due south. 2. When the watch is placed horizontally, the time at that time (24-hour system), divided by 2, points to the sun, and the 12 o'clock scale points to due north

What is the principle of keyhole imaging?