SFP (Small Form-factor Pluggable) can be simply understood as an upgraded version of GBIC. GBIC (abbreviation for Gigabit Interface Converter) is an interface device that converts gigabit electrical signals into optical signals. GBIC is designed to be hot-swappable. GBIC is an interchangeable product that meets international standards. Gigabit switches designed with GBIC interfaces have a large market share due to flexible interchangeability. Sfp Module,Epon Sfp,Gpon Sfp Shenzhen GL-COM Technology CO.,LTD. , https://www.szglcom.com
Aerial photography is to obtain a certain scale and overlap of aerial images obtained by installing aerial cameras on the aircraft and taking pictures from the air to the surface within the specified range. In most cases, the images acquired by aerial photography are tilted. Even if the ground is strictly level, the target object on the aerial camera will be deformed or displaced by the image due to the tilt of the image.
The object of aerial photography is the surface of the earth. The surface of the earth is undulating. The resulting point shift is called the on-chip projection difference. It is because of the existence of the projection difference that the conformation of the ground target object on the aerial camera is deviated from the correct position of its orthographic projection.
The characteristics of the projection difference: the closer to the edge of the picture, the larger the difference in projection; the difference in projection point at the bottom of the picture is minimal or no. The higher the elevation or target height of the ground point, the greater the difference in projection.
2, photo control measurement
The photo control measurement is a field measurement of the position and elevation of the photo control plane used for aerial triangulation (empty three encryption) or directly used for the orientation of the map.
The aerial triangulation is to use the spatial geometric relationship between the aerial camera and the captured target to calculate the plane position, elevation and out-of-plane orientation elements of the point to be determined according to a small number of photo plane control points and elevation control points. The image control point is the basis of the aerial photogrammetry analysis of the air three encryption and mapping. The selection of the position, the position of the plane and the measurement of the elevation directly affect the accuracy of the internal mapping.
The layout scheme for photo control measurement is divided into: the whole field layout scheme, the non-full field layout scheme and the special situation layout scheme.
3, the scene of the film control point layout
3.1 Whole field deployment plan
The whole field distribution point refers to the control points required in the photogrammetric mapping process, all obtained through field control measurement. The aerial camera control point does not need internal encryption, and directly provides internal mapping or corrective use. This layout scheme has high precision, but the workload of field control is large. Only in the measurement area where the accuracy of the mapping is high, the field of view is wide, the ground joint measurement conditions are good, or the small area measurement is selected.
Take the layout scheme of the stereogram map single model map as an example: a flat height control point should be arranged on each corner of the survey area, and a total of 4 flat height control points should be arranged.
3.2 Non-full field deployment plan
According to the number of routes, it can be divided into single route and regional network.
3.3 Special situation layout plan
For the special situation of joints of aerial areas, insufficient heading overlap, insufficient side overlap, waters and islands, the layout shall be carried out in accordance with the provisions of the Code.
4, the choice of field control points
Like the control point target selection: the layout of the aerial camera control point is not only related to the layout scheme, but also the accuracy of the image point measurement during the aerial survey mapping process, and various error corrections for the specific control position of the photo control point. The camera control point should meet the following basic requirements: the target image of the photo control point should be clear and easy to interpret. In order to eliminate or weaken the influence of the projection difference, it is required that the image control point is larger than 1.0 to 1.5 cm from the edge of the image. The photo control point should be selected near the midline of the side overlap; if the position of the control point is not properly selected, the result will not only cause inconvenience and difficulty to the field observation work, but also cause difficulties for the internal industry mapping work, and affect the Reduce the quality and accuracy of the internal mapping.
5, the field photo control point of the test
5.1 selection requirements for target
The target of the puncture should be selected according to the terrain, ground conditions and the nature of the photo control points to meet the specifications and contract requirements. Whether it is a plane point, an elevation point or a flat high point, it is necessary to select a target point with clear image, obvious target, and accurate stab point. The obvious target point means that the field position in the field and the image position of the photo can be clearly identified. point. A generally desirable and obvious target is the intersection of the linear objects near the right angle and close to the horizontal and the corners of the features, especially the fixed field corners and road crossings are often ideal targets for priority selection.
5.2 Image control plane coordinates and elevation test
Regardless of the plane control point or the elevation control point, the measurement work must follow the principle of “from the whole to the local, first control the broken partâ€, that is, the control measurement of the entire measurement area is performed first, and then the measurement of the broken part is performed.
At present, GPS has been widely used, and the use of GPS can greatly improve the efficiency of the field measurement measurement in the field. Using GPS network, CORS station (continuous operation satellite positioning service system), dual base station, GPS RTK and other methods, the position and elevation of the image control point plane can be quickly obtained.
6. Suggestions on using GPS RTK to arrange image control points
For the control point layout, priority should be given to the target with clear image and accurate stab. Select multiple intersections of linear features and corners of features. Curved features and shadows are generally not chosen as targets for stab points.
For the control point measurement, the position of the image control point can be displayed according to the close-up view, the foreground image shows the direction of the control point and the surrounding environment, and the image of the control point is taken in multiple directions, so that the internal drawing personnel can interpret the image control point. (a close-up view, two opposite directions)
When there is a grade road within the scope of the survey area, try to select the traffic indication on the road surface. Such as the arrow on the ground in the direction of the forward direction, the speed limit number and the inflection point, the turning arrow, the corner of the street zebra crossing, and so on.
There are houses in the survey area. When selecting the control points, it is recommended to choose the flat roof corner or the corner of the wall, and it is best to choose the corner without a shadow on the aerial camera or the corner of the north of the house (because of the photography The influence of the light on the north side of the three-dimensional model is easy to stereoscopically correct.)
When choosing a corner of the house, choose a flat house as much as possible, and the four corners of the house are clear and avoid the height of the building. When measuring the roof angle control point, the ratio of the roof roof to the ground is recorded in the entire surface of the image control point.
Within the scope of the survey area, there may be a real needle selection of target points such as floor corners, barbed wire piles, and base corners of houses under construction. However, it is necessary to consider the time interval. If the time between the shooting time and the selection time is too long and the current status of the target may change, it is not recommended to select such a target.
When the identifiable features are scarce in the area of ​​the survey area, it is recommended to prioritize the corners or midpoints of the hydraulic structures such as water diversions, bridges, gates, and culverts.
Within the scope of the survey area, the center of the communication pole pole can also be selected as the image control point. For such image control points, the left and right sides of the pole can be separately measured as reference points, and then the arithmetic mean of the plane positions of the two reference points is taken as the plane position of the pole image point, and the pole length is recorded in Like the control point, the reverse side is in the middle. (such image control points are only used as plane control points)
In the range of the survey area, when the ground object is recognized in the shadow of the photograph, the unshaded object can be drawn along the direction of the photograph, and the reference auxiliary line (extension line, vertical line, etc.) is drawn with a red pen, and then the intersection point is marked. With the intersection point as the target of the stab point, the target of the point is the image control point. (such image control points are only used as plane control points)
In the range of the measurement area, in the image display area, the artificial objects are rare, and when the identifiable objects have only the curved features, the special points of the curved objects can also be used as the target of the thorn point, that is, the image control points. Such as the inflection point of the arc of the arc channel, the midpoint of the drain pipe at the edge of the arc pool.
In the scope of the survey area, the grave can also be used as a point of control point. However, it is necessary to consider whether the shooting time and the selection time are separated from the Ching Ming Festival. The elevation and shape of the graves before and after the Ching Ming Festival may change. If the ritual platform in front of the tomb is first, consider the corner of the ritual platform to ensure the consistency of the elevation before and after the photogrammetry.
It is recommended that the field control point measurement team, preferably composed of two years of work experience, can mutually verify the interpretation of the target features and photo images. Thereby ensuring the correctness and uniqueness of the image control points.
7, the conclusion
The target selection and measurement of aerial photography field control points is the most important key to aerial survey mapping. In the field work, each measurement team member must be careful and careful, and must repeatedly read the image of the film, analyze and compare the ground target and the image of the film, and after repeated comparisons, select the obvious target of the target.
Text / "Green Technology", Zhan Yong, Huang Wei, 2014 (11)
GBIC modules are divided into two categories: one is the GBIC module used by ordinary cascade to realize the ordinary connection with other switches; the other is the stack dedicated GBIC module to realize the redundant connection with other switches.
GBIC was basically replaced by SFP for the following reasons:
SFP (Small Form-factor Pluggables) can be simply understood as an upgraded version of GBIC.
SFP module (the volume is reduced by half compared to the GBIC module, and the number of ports can be more than doubled on the same panel.
Because the SFP module is basically the same as GBIC in function, it is also called Mini-GBIC (Mini-GBIC) by some switch manufacturers.
The SFP module further compresses the size and power consumption by putting CDR and electric dispersion compensation outside the module. Used in optical communication applications in telecommunications and data communications. SFP connects the motherboard and optical fiber or UTP cable of network equipment such as switches, routers and other equipment. SFP is an industrial specification supported by some fiber optic component providers.
SFP supports SONET, Gigabit Ethernet, Fiber Channel and some other communication standards. This standard is extended to SFP+, which can support 10.0 Gbit/s transmission rate, including 8 gigabit Fibre Channel and 10GbE. Introduced the optical fiber and copper core version of the SFP+ module version. Compared with the Xenpak, X2 or XFP version of the module, the SFP+ module keeps part of the circuit on the main board instead of the module.
1 Introduction