How to Apply 3D Photogrammetry for Monitoring Tensegrity Structures Deformation - Assignment Example

ENGINEERING AND CONSTRUCTION How to apply 3D photogrammetry for monitoring tensegrity structures deformation 3D Photogrammetry is defined as derivation of 3D measurement from photographs. For instance, in the first part of this paper, there will be an effort to monitor tensegrity structure deformation by the use of the 3D Photogrammetry. As the camera captures the images, there overlapping images that are sequential that transform to three dimensional images. This is arrived at through taking a photo, by the use of auto focus ring, at a given distance, then tilting the camera to focus physically and taping the key used for the focus in place. For instance, a general and a broader example will be chosen for this particle paper. The example dwells on a mesh reflector. The mesh reflector is extensively used for apertures space aerial systems that are large due to their light weight and are packed easily and compactly. The reflector’s radio frequency exterior comprises of a mesh with reflective faces. It is bound from interlaced thin wires that are electrically conductive. This wires are made from molybdenum that are gold plated having diameters of 0.03mm. The mesh is extended over a net of cable that is made of composite filaments that are stiff and unidirectional, glued to a structure. The reflective exterior comprises of elements that due to their flexibility can be folded with ease. The accuracy mostly lies on the cable net’s shape. There are two major conceptual designs that can be spotted. The first design is based on partition of parabolic exterior in gores that get support from radial cables or radial ribs glued to an external ring. The second design is takes into consideration a separation of surfaces in facets that are flat formed by cable net tensioned using forces that are applied at each junction node. The concept has been borrowed from Miura who developed the concept of tension truss. Many large antennas that use this concept of tension truss have been launched and tested for instance Astromesh reflector and space radio telescope. The same concept has also been studied by a man called Tibert. He used the concept in designing an antenna that was based on tensegrity structure (Tibert 2002). Tension that is fairly uniform and isotropic in a reflective mesh makes sure that there is a good conductivity of electricity and RF reflectivity. The tension of the mesh should be adequate to withhold lateral accelerations that are greater than the ones having experience in orbit with no harsh distortion of the surface of the reflector. Tensions of mesh from 5N/m have been frequently used. Higher tension often efficiently smooths out mesh’s creases as a result of folding hence giving better performance of the antenna. Even tension found in the supporting net cable is nevertheless interesting from mechanical and geometrical view point. A cable that has tension that is constant and placed on a curved surface always trace its geodesic way which results to short paths hence in minimal material quantity. It turns out to be the steadiest position as it matches the configuration of minimal potential energy. In case of slight perturbation, the net cable will change its position. Net cables that have got an even tension along geodesic lines are always referred to as geotensoid. Most techniques that are availed in the open literature forms a quasi cable net through projection of a plane outline on a parabolic surface. They are at times approximated by a surface that is spherical. The accuracy is then improved by changing of the position of the node with optimization algorithms or iterative approaches (Tibert 2002) A method was proposed by the same person called Tibert. Nevertheless, the proposal has resulted in tension variations in the element of cables. In all the cases, as these approaches can’t guarantee an even tension in net cabling, they are not in a position to generate the real minimum tension truss length configuration. In this piece of work, it can be proposed that a method that is innovative should be applied in generation of cable nets having even tension and having surfaces that are exactly parabolic. Firstly, an approach is presented that is based on method of force destiny and mechanical consideration used. The space antennas require an error that is very low shaped for the parabolic surface. Secondly, another source of error should be faceting after production, whether it is as a result of deployment repeatability, thermal distortion or mesh saddling. Therefore, considerations are taken into place on accuracy of worked out surfaces by approximating the faceting error (Tibert 2002) 3D photogrammetry Photogrammetry is defined as derivation of 3D measurement from photographs. Latest technology advances in computer processors, computational techniques and digital cameras make this technique a powerful and portable one yielding extremely accurate and dense 3D data having limited photos captured using set digital photography tool, in short duration of time. Five years down the line, the power and variety of photogrammetry have improved noticeably. SF photogrammetry which is structure derived from motion finds a subject’s 3D structure by analysis of field motion of projected 2D created by continued change of camera sensor’s position in relation to its subject. Both SFM and photogrammetry need sets of digital image that takes record of the relative transition in points between the subject and the view point of the camera (Poke et al 1984) .The motion is noted by the pixel referencing subject locations in a photograph being matched with pixel referencing similar location in additional photographs. The photographic sequences that were captured in accordance to the principle that capitalize on information got from this view point change yield best outcomes. These data that are rule based independent form software platform. The platform can be reused in the future. How it works The most important element in having a successful process of 3D photogrammetry is by getting quality photographic sequence which is based on simple principle. In the camera capturing process, the initial step is the calibration sequence. This sequence maps and determines the visual distortions that occur in lens with reference to sensor location. The step can be attained if there are many common points between calibration sequence images that overlap. The photographs from the camera calibration should be captured using similar settings like for overlapping photos. Not less than 4 additional photographs are required. The first two photos should be taken by rotating the camera 90◦ to the prior overlapping photos line. The other two will be taken by having the camera rotated at 270◦. These additional photos should be captured at any place that is in line with overlapping photos. Nevertheless, the best outcomes occur in places where many correlated points stands to be generated. The aperture of the camera should be constant during the sequence of capture. On a camera of 35mm, the aperture should not be set less than f/11. Moreover, having apertures that are less than f/11 can cause diffraction effects to appear which blurs images hence substantially reducing the resolution of the camera. The lower the ISO settings in the camera, the lesser electronic noise produced in its sensor. Therefore, a lower ISO setting is always preferred. This is because if the setting is high, the noise produced will be high hence making the pixel matching in different photographs difficult. The ultimate accuracy of resultant thick surface model is either governed by GSD or image resolution. Image resolutions are directed by no of pixels in a given area. The resolutions are also directed by the sensor’s size. The setting of the camera should be preferably between f/5 and f/11 and the set standard, white balance, and shutter speed among other settings should be attuned to attain well exposed images. In order to achieve the highest outcome, it is vital to make sure that the zoom and focal distance do not alter for any sequence of photographs. This is achieved through taking one photo, by use of auto focus key, at a preferred distance, then changing camera to focus manually and taping the ring used for focusing in place. For maintenance of a constant 66 percent overlap, the machine (camera) should be made to move a distance of 34 percent in a direction adjacent to taking one photo view field. To ensure that that the whole subject is enclosed by more than two photos overlapping each other, the photographer should place the subject’s left extent in the middle of the 1st frame. The following step is proceeding from the left to the right along subject’s length and takes many photographs for complete coverage. To achieve high quality outcomes, the camera should be rotated 90 degrees. 66 percent overlap should also be used over the area of capture. After which the camera should be rotated 180 degrees to capture the same area. As the technique is flexible, there is a possibility of obtaining 3D data that is highly accurate from subject of any orientation the camera place. Nevertheless, it is vital keeping the sensor’s plane and lens analogous to subject and maintaining a constant height from subject. For provision of measurability, there should be placement of scale in image sequence. It must also be in more than one photo. Placement of the scale may be done anywhere in the view field inclusive of the edges and corners of the work. The effects of optical distortion, that is as a result of placement of scales near corners or edges of the view fields, which stretches an ordinary photo scale, is rectified by photogrammetry software. Moreover, the main function of the scale is to provide an introduction of real measurement value to the focus. The role is achieved by addition of an object whose measurement is known which can be seen in more than one stereo model. There is a preference to have more than one of those objects to make sure that there is accuracy and visibility assessment. The objects may later be given their real length when being processed. . Bibliography A.G. Tibert. Deployable tensegrity structures for space applications, Department of Mechanics, Royal Institute of Technology, Sweden, 2002. Brian W. Kernighan, Rob Pike. Aids in Mixing and Matching Programs. Encourages Exploring & Experimenting With Program, 1984 Read More