With the rapid development of China's social economy, the value of real estate is increasing accordingly, which makes the country pay more and more attention to real estate surveying and mapping, and the requirements are higher and higher.
Real estate surveying and mapping is an important branch of surveying and mapping field. General surveying and mapping of real estate includes surveying and mapping of real estate, cadastral surveying and mapping, survey of forestry resources, survey of grassland resources and survey of sea books, etc. The main objects of surveying and mapping of real estate and cadastral surveying and mapping are the area, ownership, structural attributes and utilization status of urban and rural houses.
Traditional real estate surveying and mapping has not been a good solution to the problem of heavy workload, long time and high cost. Inclined Aerial photography is a new technology developed in recent years. Based on the characteristics of inclined photogrammetry model reconstruction technology, such as low cost of data acquisition, high efficiency and good presentability of reconstructed 3d model, the application of inclined photogrammetry 3d modeling technology in real estate surveying and mapping has many advantages.
一、Real estate mapping method based on 3d modeling of tilt photography
1、Oblique Aerial photography data acquisition
Unmanned aerial vehicle (uav) oblique photography is five oblique photography by carrying on unmanned aerial vehicle (uav) system, one of the lens for ground targets are projective like, the rest four cameras to collect ground targets before and after, left, right four directions of tilt images, and can get contains images in an instant information such as location, altitude, POS data.
Ultra-low altitude flight; That is, the uav's aerial height is set to about 60m, so as to obtain images with higher ground resolution and ensure the accuracy of 3d model reconstruction. If the height difference in the survey area is large, the image should be collected and modeled by division.
Dense phase control; That is, an image control point is arranged every 200-300m or so, with no less than 9 image control points per square kilometer, and phase control should be done in advance to reduce the geometric distortion of the model at a distance.
2、Reconstruction of 3d model of oblique Aerial photography
The 3d model reconstruction of oblique photography is realized through multi-view image joint adjustment, multi-view image dense matching, namely multi-view stereo matching based on object square, construction of TIN grid, texture mapping and so on.
Among them, the joint adjustment of multi-view images is based on the geometric deformation and occlusion problem between images. Combining with POS data, the same name point matching and free network beam adjustment are performed on each level of images. Intensive multi-vision image matching refers to the retrieval of feature points and feature lines on multi-vision images to determine the two-dimensional vector data set, and then the two-dimensional data sets from different perspectives are transformed into three-dimensional vector data, which are then filtered and fused to form a unified digital surface model (DSM).
The real estate mapping method based on 3d modeling of oblique photography firstly preprocesses the oblique image data, that is, checks the image quality problem, and adjusts the color difference of the image to reduce the influence of model accuracy caused by the inconsistent light contrast and intensity of each image at the moment of exposure of oblique photography. Check POS data to eliminate images with bad posture.
Then the pre-processed oblique image is imported into Smart3D for space tripping and generation of digital surface model (DSM) and digital orthophoto image (DOM). The generated digital surface model (DSM) and digital orthophoto (DOM).
二、Compared with traditional real estate mapping has advantages
In this paper, the three-dimensional modeling technology of uav tilt photogrammetry is applied to real estate surveying and mapping. According to practice, compared with the traditional surveying and mapping operation method, the following advantages are obtained:
（１）Compared with the traditional real estate surveying and mapping, there is no need to enter the courtyard for surveying and mapping; only image control in the open zone is required to obtain the real three-dimensional model through the processing of inclined image, and the accurate figure of buildings in the courtyard can be obtained through the five-point acquisition of the model.
（２）Compared with the traditional surveying and mapping operation, the porch, eaves corridor, overhanging corridor and other ancillary facilities can be directly collected on the three-dimensional model, without the need to select projection points on the ground, reducing the error caused by human factors; Moreover, 3d mapping can be used to collect data from multiple perspectives. Compared with the blind area of the total station, the error caused by the fulcrum in the complex terrain is reduced and the advantage in accuracy is highlighted.
（３）Compared with the traditional surveying and mapping operation, the adjustment of eaves correction, layers, attributes, etc. is eliminated to reduce the workload of field adjustment and mapping, so that a large number of field work can be turned into internal work, which facilitates the efficient and rapid completion of surveying and mapping tasks and greatly reduces the operating cost of measuring units.
（４）It can be carried out on the three-dimensional model to reduce the influence of weather factors on the delay of outdoor work.
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