Some of the issues we would like to present: The validity of hybrid recording systems- theodolite + laser scanning + photogrammetry

OBSERVATIONS:

• The theodolite will serve as a tool to obtain x,y,z co-ordinates. It will guarantee the accuracy of the survey. Therefore, the laser scans and photogrammetric 3D outline can relate to these measurements.

• Photogrammetry is very accurate for outline restitution. However it is less ideal for very complex textured surfaces such as the templates.

• Laser scanning is ideal for surface texture etc. It is less ideal for outlines.

• The best solution is to combine the three systems. The theodolite for precise measurement of the whole. The photogrammetry for precise outline drawings of the various stone blocks. The laser scanning for the precise texture of the stone blocks.

• This hybrid system will prove more accurate and economical.

A) PROPOSED METHODOLOGY FOR THE SURVEY

(Two methods are possible with our system. Either combining the photogrammetry co-ordinates system into the laser software or inserting the laser co-ordinates system into the photogrammetry software).

1)   Theodolite

2)   Laser scanning

3)   Photogrammetry

4)   Consolidation of photogrammetry co-ordinates in laser scanning software or Consolidation of laser co-ordinates in photogrammetry software.

5)   Creating a triangulated surface (meshing)

6)   Texture mapping from photogrammetry

1)   THEODOLITE

The theodolite will serve as a tool to obtain x,y,z co-ordinates. It will guarantee the accuracy of the survey. Therefore, the laser scans and photogrammetric 3D outline can relate to these measurements.

With the theodolite several 3D co-ordinates could be made in the same co-ordinate system. X,y,z co-ordinates are registered by using either cross haired targets or spheres with an integrated prism. (The bases of the spheres are fixed on stands to identify the exact position of the sphere before removing it). This data is saved as a neutral file with co-ordinates.

2)   LASER SCANNING

Laser scanning is ideal for surface texture etc. It is less ideal for outlines.

The laser scanner can produce thousands and millions of very accurate 3D co-ordinates. This survey is very ideal for the collection of information of the stone block texture. Spheres without an integrated prism are used for consolidation. Some of these are to be placed in the same position as those used for the theodolite. A grid is selected depending to the level of detail required.

3)   PHOTOGRAMMETRY

Photogrammetry is very accurate for outline restitution. However it is less ideal for very complex textured surfaces such as the temples.

The photogrammetry survey (in parallel with the theodolite) can produce a very precise outline in three-dimensional points. This is done by using stereo pairs of photographs. In the photogrammetric survey the targets used are the same ones used for the survey with the theodolite.

4)   Consolidation of photogrammetry co-ordinates in laser scanning software or Consolidation of laser co-ordinates in photogrammetry software.

Once the three systems are complete they are combined into one integrated system.

5)    Creating a triangulated surface (meshing)

Information obtained by the three systems (x,y,z co-ordinates) are converted into a triangulated surface over which texture mapping will be applied.

6)    Texture mapping from photogrammetry

The images taken during the photogrammetric survey can be also utilised for texture mapping.

USEFUL SOFTWARE FOR THE CLIENTS:

a)     Realworks is presently free of charge and can be down loaded from Mensi website. You can export points from 3Dipsos (it is the laser scanning software) to Realworks. With the Realworks viewer you can visualize and explore as built data acquired by the laser scanning. Through Realworks a 3D cloud of points may be visualised. It may be rotated, translated and zoom in or out in order to explore data in detail. Visualization may be done in different ways. Points shaded by intensity, by colour etc… A 3D cloud of points may also be compared to a 2D image.

The possibility to use the segmentation function (for sectional plans and elevations) will become available in 2 months time.

b)    3Dipsos (it is the laser scanning software) can display all the information available, for eg. view cloud of points, view and produce meshing and texture mapping. It is also possible to take measurements. It is possible to produce sectional elevations and plans using this software.

c)     Compatible software for the user to be able to use the survey: Autocad (file format DWG or DXF) or Microstation (format DGN) for viewing and manipulating the vector data, and Photoshop (or similar) for viewing the TIFF output.  For viewing geo-referenced imagery (i.e. to retain registration between vector data and imagery) Microstation is recommended. 

d)    For viewing the imagery and data in stereo DiAP Viewer ( it is the photogrammetric software) is required and Bently Microstation is essential. (Various discounts exist on this software). In this case, it is very easy to produce cross sections once the surface mesh is finalised.

e)     You can export meshes in DXF format and then transfer to AutoCAD software. You can export meshes and texture mapping in OBJ format and transfer information to 3d Max and some other 3D animation or CAD software. DXF and OBJ format can be used with 3D exploration (from “Right Hemisphere”) to display or export in other formats.  You can also export a list of points or a group of list of points in DGN format.