Study 1 - From 2d Base Map to 3d City Model - Matti Arponen - City Survey Division, City of Helsinki, Finland
Laser-scanning and digital photogrammetry have been used in collecting 3d information on map objects in Helsinki. These methods have been applied in mapping out dated map features and in producing 3D models manually, semi-automatically, and automatically. It is noted that it is as much a software development project as it is a 3D city model project.
Some of the problems encountered in this effort (and some i can relate to) include:
finding quality data sufficient for 3D
how should this be connected to the bigger picture of the cities CAD base
Is there enough height information
how can the skills of 2D draftsmen translate to 3D
how is the model to be updated
what level of detail is to be modelled
In this case there were 3 models at 3 scales: a rough city model, a precise city model, and a textured precise city model.
The textured and precise city models have been produced by using a combination of facade photographs and manual and automatic modelling techniques.
The products used in this instance are TerraModeler, TerraScan and TerraPhoto, which re under constant development.
Gathering height information is a big project. Height modelling by an operator using stereo photogrammetric work or interpreting laser scanned points (ground level, buildings, edges of the street elements as break lines would take up to 25 years in this case. Laser scanning as a method to gathering info is being experimented. The problem with these methods are, unlike stereo mapping where only a few points are targeted and measured, the scan picks points which may be of no interest, like humans, traffic lights etc so it may take some time to use this information. The benefit of coarse is the level of detail.
http://cumincad.scix.net/cgi-bin/works/Show?_id=a35a&sort=DEFAULT&search=photogrammetry&hits=37
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