Summary of final work on the topic
Contents
- Introduction
- 1. The purpose and objectives of the study, expected results
- 2. Drafting ground photogrammetric survey
- 3. Image processing
- Conclusion
Introduction
Photogrammetric surveying methods are the most cost-effective and high. The main advantage of the method is the photogrammetric a significant reduction in the time of field work, the ability to repeat or supplement measurement at reference conditions. The disadvantage is that the quality of the image depends on the lighting level, foreign objects can create dead zones in the images.
The existing analog cameras like phototheodolite obsolete, and, moreover, are not produced analog light-sensitive materials. Professional Digital cameras are expensive and, with small amounts of ground surveys, their use will be unprofitable. Non-specialized digital cameras make it possible to obtain an image in digital form and also perform image processing on digital photogrammetric station. Therefore it is necessary to determine the accuracy of such treatment.
To solve the problem of studying the monuments of architecture, monitoring deformations structures requires their accurate images. Determination of field size facilities to carry out measurements of models designed for such installations, forms which can not be expressed in mathematical equations - sculptures, reliefs, etc.
1. The purpose and objectives of the study, expected outcomes
The purpose of master's work is to validate the use of non-specialized cells for the purposes of stereophotogrammetric architectural photography. You must solve the following research problem: determine the accuracy that can be obtained at stereofotosemke architectural object, using nonmetric camera. Applied research objective is to compare the resulting model model built with the help of an electronic instrument.
Based on the obtained results and the accuracy of the comparison would be the optimum method of creating three-dimensional models of architectural objects.
The object of this study is ground stereophotogrammetric survey. Item - accuracy, which can perform non-specialized camera.
2. Drafting of the groundbased photogrammetric survey.
The first stage of experimentation was ground stereophotogrammetric survey. The subject of photography was the facade of the 5th Corps DonNTU, shooting 5 megapixel camera made Olympus E-20P.
Types of ground stereophotogrammetric survey are classified according to location axes of the camera relative to the base. When shooting converged case is used photography, the basis of 4 m
Figure 1 - The case of Convergent photography
In the case of convergent photographing optical axis of the cameras intersect, object coordinates are determined by measuring stereoscopic. In the beginning of photogrammetric coordinate system take the optical center of the lens on the left at the basis of photographing, ie, the center of the projection of the left image, with the y-axis - the direction of the optical axis of the camera to at the left base, perpendicular to his direction in the horizontal plane - for the x-axis X-axis for the applicate - the direction perpendicular to the plane formed by the axes X, Y.
The value of exterior orientation required for photogrammetric ychisleniya coordinates determined in the process of photography. The elements of interior orientation are known.
After selecting the plants begin to design bases, which must satisfy the following requirements:
- Shooting a trapeze to cover the entire area with no removable discontinuities and high ceilings. The ends of the bases are located in convenient locations;
- Within the survey should not be a trapezoidal areas, which are not visible object or stereo.
To calculate the trapezoidal frame shooting formulamy use the following:
where tmin - coefficient taking into account the deviation of the axes shooting (we take 1); mp - accurate removal of the coordinates of the image; mr - allowable M.S.E. determine the coordinates of the contour.
Based on the calculations and the selected camera, the position is scheduled basis. At each shooting position trapezoid outline proof-points. These are points for which the known geodetic coordinates of the measured (reference point) or direction (the angle between the direction of the corrective point and direction of the base). Control points will be obtained from the survey results in the total station reflectorless mode.
The calculation is performed based on the length of the basis of the photographing distance and the required accuracy of the coordinates of shooting pickets.
Predraschet accuracy can be performed as follows:
where ml - M.S.E. shooting picket (1 cm); mx = my = mp = 0.5 pixel.
3. Processing of images
The next step was the processing of stereo pairs with DPS Erdas Imagine.
Each project file created in Erdas Imagine contains information on all routes and photographs included in the plan of shooting. In particular, the location of images, camera parameters, measurement of fiducial marks, ground control and tie points.
When applied to images, control points, previously obtained from tacheometry reflectorless mode, enter manually, and the coordinates of the additional points are determined automatically. Mathematical relationships between images that make up the block, set with the triangulation, and in the process of its implementation of the final calculated values for the parameters of exterior orientation. The report provides an assessment of the accuracy of triangulation adjustment stereo.
Arrangement of stereo imagery, ground control and tie points after equalization is presented. The field of this project ready for the final part of creating a digital model.
Figure 2 - Arrangement of pictures after the adjustment.
In the process of drawing lines, we used structural Planar Dual-LCD Professional 3D Mnitor, you can view three-dimensional image quality. This allows you to speed up processing, it significant impacts on usability.
The next step was the processing route in the DPS Delta Digitals.
And so, were obtained by two 3-D digital model of a single object. Because of the different algorithms for equalization models are obtained. Impact longitudinal and transverse parallax greater than the model equations in Erdas Imagine, respectively, the model equations in Block MSG geometrically accurate. Time to build model of the digital stations were spent almost the same, but to work in stereo mode much more convenient.
The disadvantage of this experiment is that eference points were used to orientation parameters are indicated on the object with marks during the shoot, respectively accuracy is reference point in the image could reach 30 millimeters in the area, significantly the accuracy of model building, respectively, determine the accuracy of the results can not be considered objectively.
Figure 3 - Model of the subject.
This drawback was taken into account by repeating an experiment.
Also, during the field work were determined cooordinates of the camera in time of shooting, so that further investigate whether this will improve the accuracy of model building.
Figure 4 - Status of implementation of field work.
Conclusion
As a result, the work will be received three 3-D model of the subject. One model will be built conventional method (based on tacheometry), two more models will be obtained in different DPS (because of the different algorithms for equalization in the DPS obtained models will vary).
Photogrammetric method of constructing the model has a huge advantage in terms of ease measurements, as the original data stored in computer memory and, if an error occurs, there is no need in repeated measurements of the field, do the field work took much less time cameral processing is done relatively quickly.
The accuracy of the method of obtaining the coordinates tacheometric obviously higher, but for a number of problems will be sufficient accuracy, which can be achieved photogrammetric method. Comparing all the figures and characteristics of both methods, you can draw conclusions about the feasibility, profitability, complexity of the application of photogrammetric techniques and tacheometric.
In writing this essay master's work is not finished yet. The final completion - December 2012. The full text of the work and materials on the topic, may be obtained from the author or his head after that date.
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