[Imports] San Francisco building heights import
bdon at bdon.org
Sun Nov 27 01:39:55 UTC 2016
We will start adding tags this week. A list of usernames that will be
performing the tasks is here:
Tasks will be tracked at a new project on the main openstreetmap.us
Other questions and comments can be put in our GitHub repo or Gitter channel.
We're also arranging for a community mapping event in San Francisco.
On Fri, Nov 18, 2016 at 4:25 PM, Brandon Liu <bdon at bdon.org> wrote:
> Hi Christoph,
> For data accuracy:
> Yes, our goal is to automate the tagging for flat-roofed and
> unobstructed buildings. Sloped or uneven roofs and trees can be
> identified in the JOSM hillshade tileset . Mappers will then refer
> to the raw LIDAR or street level imagery to determine the correct
> We want to prepare for mappers a complete set of tools and imagery to
> create an accurate dataset. We believe the result will be up to the
> standards of height data elsewhere in OSM. It should also be better
> than a mapper on foot could estimate without special equipment.
> For the community:
> I don't believe that this import will discourage community mapping. I
> used the Overpass API and found only 424 edit actions since 2012
> adding a height tag to a building in San Francisco. Details are on
> GitHub here .
> Two users are responsible for 65% of these building height edits.
> There are only 10 users total who have added a building height tag to
> more than 2 buildings. I have messaged all these users, inviting
> comments on the wiki. These results suggest to me that heights are not
> a current focus of mapping in the affected area.
> I do think that getting started with building heights will encourage
> further mapping. A complete 3D dataset like in New York City is a
> great showcase for OSM data and attracts new users. Getting to a
> similar level of detail in San Francisco is a compelling goal for the
> local community. We've had offers to help from local meetup groups and
> companies that are excited about the project.
>  https://wiki.openstreetmap.org/wiki/San_Francisco_Building_Height_Import#Failure_Modes
>  https://github.com/osmlab/sf_building_height_import/issues/21
> On Thu, Nov 17, 2016 at 9:41 AM, Christoph Hormann <chris_hormann at gmx.de> wrote:
>> 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
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