First of all thanks for doing a more elaborate preparation than back in May. The whole process is now much clearer.
To verify my understanding: the height values you assign are the median height values of the city footprint data set when there is a matching footprint within the area percentage cutoff chosen. This median height value is the median height in the 0.5m gridded data set within the city dataset footprint that has been calculated as the difference between a gridded first reflector data set and a gridded ground level data set, both derived from the raw LIDAR data. I am sure this often leads to fairly reasonable results, in particular with flat top buildings and flat ground with no significant structures except the buildings but it does not appear to be a really good approach in principle. Sources of error here are not only the systematic error with non-flat roofs, the footprint mismatch and obstructions of the roof. Likewise important are the inaccuracies introduced by the grid sampling step and ambiguities in the ground level definition like plants, cars and non-building structures. These technical things aside i am not sure it is a good idea to enter this kind of data in OSM. This likely won't encourage community mapping and it will be of little gain for data users. Producing a separate point data set with the height values that can be easily matched with the OSM geometries would IMO be better. You could then also replace the fixed geometry matching cutoff with a reliability attribute and data users could decide how strict they want to be in that regard. -- Christoph Hormann http://www.imagico.de/ _______________________________________________ Imports mailing list [email protected] https://lists.openstreetmap.org/listinfo/imports
