Laser scanning to the lush foliage, towering trees, the elevation between the laser pin point the local discontinuous situation, but its manifestations are significant differences with the former. The closer the distance between two adjacent points, the greater the height difference between two points, the less likely the high point in the terrain surface, therefore, to determine whether at the surface of the terrain, to take into account that point to a point of reference terrain ground points the distance, with the increase of the distance between two points, the threshold of judgment should be relaxed, taking into account the rugged terrain elevation changes. The two ground points farther away, the greater will be the natural elevation. The laser data splicing. Airborne LiDAR operations, due to the flying height and scan field of view angle limit to complete the operating area must be flying the route. Of course, if the customer needs the green laser pointer .
And these routes must also maintain a certain degree of overlap (10% -20%). However, due to the presence and influence of various errors, system errors and random errors in the the DTM splicing two strips. Airborne LiDAR can help take the image of the ground, according to the overlap region between the strips can determine systematic errors, thus eliminating the systematic errors between the flight strip. Splicing the correct order to make the survey area DTM, you must also eliminate the random error between the flight strip, you can use the weighted average method for a variable coefficient. Rr for the current DTM points overlap go to the far right distance from Rl to the overlapping area of the left-most distance Hr DTM value of the right side of the overlapping area, Hl, overlapping the left of DTM value. It is according to the customer’s feedback and requirement towards green laser pointer .
This consideration is the form of line scan system, with the scan angle increases, the positioning accuracy of the system decreased (Lau Siu Chong 1999), based on theoretical analysis. Due to the complexity of the flight, each line scan data overlap between the two routes are not the same, so the weight coefficient changes with every line, each pixel in each line is change, so to ensure the overlapping area to the the smooth transition of non-overlapping, truly seamless. Classification output of the laser data. After data classification, unnecessary data is removed, will reduce the amount of data, data files will also be reduced when the surface is relatively smooth (eg, ground, power lines or buildings, etc.) is reduced by a big margin, but as vegetation such as less decreased. Finish green laser pointer as per requirements of the customer.
Classified data can be output in ASCII or binary form. POS Dynamic Positioning positioning results to the WGS-84 coordinate system, we need aerial triangulation encryption results belong to a national coordinate system or local coordinate system, and therefore must solve the problem of positioning the results of coordinate transformation. Standing in the precisely known ground-based reference WGS-84 coordinate system, and known to the transformation parameters between WGS-84 coordinate system to the national coordinate system, can be dynamic positioning converted to a national coordinate system coordinates, the general is the use of GPS baseline vector network constraint adjustment. Another problem is that the vertical datum problem. Provided by the GPS positioning is based on an ellipsoid earth elevation as the base. green laser pointer needs the manufacturer pay more attention to solving it.
The actual need based on the geoid for the normal elevation of the benchmark, vertical datum conversion fitted through the control points of the survey area a number of known normal elevation of the establishment of height anomaly model (when the measurement of topographic change should be added terrain correction). Orientation and mosaic of the image data. The first digital image to extract and process, and then combined with aerial photos of the inside and outside the party elements, aerial triangulation, DTM data and then combined with laser scanning directional mosaic, the formation of the orthophoto map (DOM). The laser data processing software. Enormous amount of data generated by LiDAB existing measurement software is difficult to adapt to deal with such a large amount of data, therefore, require special software to handle. It is revising the technology of laser pointer .
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