The City of Helsinki, Finland, is currently involved in a conversion and upgrade project to supplement its digital 2D basemaps with a new, accurate 3D model.

Leading this migration from 2D to 3D is the Helsinki City Survey Division, which employs 142 people, 40 of whom work in its GIS center. The City Survey Division is responsible for all city mapping functions, including maintaining of a geodetic network, basemap and utility map 1:500, legal maps for city planning, topographic maps, and tourist maps. Additionally, it is responsible for maintaining the legal parcel cadastre and surveys, parcel IDs, building IDs, aerial photography, parcel addresses and updates, and the city’s Web GIS services and GIS coordination.

Although some 3D work had begun as early as 1986 for city planning and construction projects, most of the work began in earnest in 1997 in response to increased demand from other city organisations. The maps and database are used by City Planning, Public Works, Helsinki Energy, Gas, and Water departments, as well as Helsinki Harbour and the Public Transportation Authority.

From 2D to an accurate 3D model
With the help of Bentley products such as MicroStation, MicroStation GeoGraphics, InterPlot, Descartes, and I/RAS B, the Survey Division has been taking 2D basemaps at a scale of 1:500 and converting the data to an accurate 3D city model. As new data is gathered, the GIS and 3D databases are continuously and automatically updated, ensuring all departments have access to current information. Laser scanning and aerial digital photogrammetry are used to gather 3D information on as-built and terrain objects. Using the digital photogrammetry to produce orthophoto mosaics, these orthophotos, along with the laser point clouds, have subsequently been used in mapping outdated features and in vectorizing buildings and streets in 3D. The modeling process is enhanced with thirdparty software packages developed in Finland that run on top of MicroStation, and are suited for airborne and terrestrial laser data applications.

Three scales of the city model
In 2002 a general 3D model of the whole city was completed from the city’s building cadastre, orthophotos, and current 2D/3D basemap. This model was used in the Helsinki Master Plan 2002 project, which was later approved by the Helsinki City Council. Three scales of 3D models are used in Helsinki—a general 3D city model, an exact 3D model as the new 1:500 basemap, and an exact 3D model with textures included. In these models the Survey Division can provide its users a variety of information such as building cadastre information, streets (breaklines), trees, and vegetation. It can also add orthophoto coverage on land and facade photos to the buildings. The maps and models are currently used in city and street planning, civil engineering projects, soil surveys, building permit processes, noise modeling, traffic simulation, and military defense applications.

The Survey Division has made much progress since the project began, and is working diligently at converting the entire city basemap to 3D. Progress can be slow because there are still issues with the conversion methods, as some of the new 3D basemap objects are preliminary or are under construction. Additionally, some of the old 2D basemap features have digitising errors which take time to correct, and the 3D modelling is more timeconsuming than 2D. However, much of the city has already been converted.

In most if its planning, construction, and infrastructure maintenance tasks and processes, the City of Helsinki administration will continue to move to using the 3D basemaps as a standard.