VISUALISATION OF ST TRINITATIS CHURCH IN LIEPAJA, LATVIA
Objectives of the project were to
1)create a 3D model of St. Trinitatis Church in Liepaja, Latvia
2)create a system for the observation and visualisation of potential settling of the church columns and other structures to study the possibilities to use this pilot observation system in other valuable buildings of cultural heritage
3)develop the 3D modelling know-how and to get acquainted with a new 3D modelling technology, laser scanning
4)experiment the usage of virtual reality Cave in a visualisation of a large 3D model
When 3D-Bridge project was outlined, we had figured that all these measurement would have been done with a tachymeter. When the project started, we had received some quite promising examples of laser scanner measurements and we decided that 3D modelling task would be performed with a laser scanner. The measurement points needed for calculating the settling of the columns will be done with a tachymeter, since it is very precise and the measurement accuracy is not dependent of different surface materials and colours like it is in the case of laser scanning.
We were not prepared to the huge amount of 3D point cloud material we received after the measurements. This was quite new technology to us and we needed special tools to post process the data. The next step was to triangulate the vast 3D point cloud material – tens of millions of 3D points – to form 3D surfaces called meshes. It turned out that the any of the software packages that we have available were not capable of handling these enormous amounts of 3D points, even though the material was sliced in pieces To solve this problem a survey of suitable commercial and open source software solutions was done. We found out that there were no open source software available for the triangulation of the point vertices, and commercial software packages were too expensive. Rental of the software and purchasing education for using it were the only thinkable solution. Simultaneously along the 3D modelling work, we tried to find the best way to demonstrate the settling of the church.
3D modelling work continued with the following tasks of which we are currently in phase 2
1.triangulation of the point cloud to a 3D mesh
2.reduction of the 3D mesh by removing unnecessary polygons/triangles
3.creation of the textures
4.application of the textures
5.testing of the model in the Cave environment, and possible iteration between stages 2 to 5
6.creation of the visualisation information for the settling of the control points
More photos will be shot and control measurements for settlements of the church will be done during the next visit to Liepaja, Latvia. These photos will be the ones to create the texture images from. The images for the textures should cover larger areas, such as one whole wall in one photograph. These control measurements will be done with a tachymeter, not a laser scanner. Only the control points attached to the pillars and other solid structures of the church will be measured, and finding the best way to visualise the difference between the points measured six moths earlier is one of the tasks.
In modelling work we have got few problems, and the biggest one was the huge amount of data involved with laser scanning.
Second problem related to the first one – there were no open source software libraries or programs available to do the triangulation and reduction job.
