Latitude measured north from the equatorial plane of the earth. The symbol is n. From 0 to 90 degrees north latitude. A latitude on the earth. The latitude of a point on the ground on the reference ellipsoid, that is, the angle between the normal of the reference ellipsoid passing through the point and the equatorial plane of the earth. It does not consider the uneven distribution of matter in the earth and the influence of topography, so it is different from astronomical latitude. However, geographical latitude is revised from astronomical latitude. It differs from astronomical latitude by no more than 30 ". Generally speaking, geographical latitude refers to this. North latitude measured from the equator to the north; To the south, it is "south latitude" (S). From 0 to 90.
east longitude
The longitude measured from the prime meridian to the east is called east longitude, which ranges from zero to 180 degrees.
latitude
Determination of longitude and latitude
On maps and globes, we can see horizontal and vertical thin lines, much like Fang Gezi on a chessboard. They are longitude and latitude. According to these longitude and latitude lines, the position and direction of any place on the ground can be accurately determined.
How are these longitude and latitude lines determined? The earth is constantly rotating around the earth axis (the earth axis is an imaginary line passing through the north and south poles of the earth and the center of the earth). Draw a great circle perpendicular to the earth axis in the middle of the earth, so that every point on the circle is equal to the distance between the north and south poles. This circle is called the equator. On the north and south sides of the equator, many circles parallel to the equator are drawn, which is the "weft circle"; The line segments that make up these circles are called parallels. We set the equator as zero latitude, 90 degrees south latitude to north, south latitude to south, and north latitude to north. The North Pole is 90 degrees north latitude and the South Pole is 90 degrees south latitude. Latitude also marks the hot and cold climate, for example, there is no winter in equatorial and low latitudes, no summer in polar and high latitudes, and four distinct seasons in middle latitudes.
Secondly, from the North Pole to the South Pole, you can draw many great circles whose north-south direction is perpendicular to the equator of the earth, which are called "meridian circle"; The line segments that make up these circles are called meridians. In A.D. 1884, it was internationally stipulated that the longitude line passing through Greenwich Observatory in the suburb of London, England, was taken as the starting point for calculating the longitude, that is, the longitude was zero minutes and zero seconds. Its east is east longitude, *** 180 degrees; It is west longitude, *** 180 degrees. Because the earth is round, the longitude of east longitude 180 degrees and the longitude of west longitude 180 degrees are the same longitude. Countries have designated longitude 180 degrees as "international international date line". In order to avoid using two different dates in the same area, international date line will be slightly biased when it comes to land.
Each longitude and latitude can be further subdivided into 60 minutes, and each minute can be further subdivided into 60 seconds and fractions of seconds. Using latitude and longitude lines, we can determine the specific location of every place on the earth and express it on a map or globe. For example, what is the latitude and longitude of Beijing? We can easily find out from the map that it is east longitude 1 16 degrees 24 minutes and north latitude 39 degrees 54 minutes. A ship sailing in the sea can determine its position and direction in the ocean as long as it measures the longitude of its position.
The latitude is 90 degrees. The equator is 0 degrees, and it is arranged towards the poles. The smaller the circle, the greater the degree.
What is a baseline?
It is still difficult to understand the definition of baseline only from the concept defined in CMM. If the three concepts of checkpoint, milestone and baseline are explained and compared together, it will be easier to understand the baseline. That's what I did. Enjoy it.
Checkpoints, milestones and baselines are very important concepts related to time in the project life cycle.
Checkpoint refers to the inspection, deviation analysis and corresponding plan adjustment of the project within the specified time interval.
The interval between checkpoints should not be too long, otherwise the purpose of inspection will be lost. In the projects I have participated in, the interval of checkpoints is usually once a week, in the form of weekly meetings or in-depth inspections between project managers and quality control departments.
Milestone is the symbol of completing the stage work. Milestones are different for different types of projects. Setting milestones in the project life cycle can reduce the risk that the schedule will not be completed on schedule.
There should not be too many milestones, otherwise the management cost will increase; Not too little, or the purpose of detail management will be lost. The projects we implement are basically software development projects, and the milestones are basically set according to the implementation stages such as startup, planning, demand analysis, design, development, testing, training and trial operation.
Baseline refers to a state in which a configuration item (or a group of configuration items) is formally controlled through formal review at different points in the project life cycle.
In this way, it can be understood that the baseline is actually some important milestones, but the relevant results produced by the milestones have to be formally approved and used as the baseline and starting point for the follow-up work. Once the baseline is established, the change needs to be controlled. In software development projects, the completion of requirements analysis and design can be set as a milestone. However, the demand analysis report, as the result of the demand analysis stage, will establish a baseline as the benchmark for subsequent design work after review and confirmation. If the requirements analysis report is modified, the application needs to be changed.