[Talk-ca] Building Import update

Nate Wessel bike756 at gmail.com
Sat Jan 26 18:59:09 UTC 2019


Building count doesn't really have anything to do with preserving 
topology, and I'm not sure a visual inspection would cut it - Can you 
look at the documentation for this tool and verify that it preserves the 
topology of polygon layers?

This is a good illustration of the (potential) problem:
https://trac.osgeo.org/postgis/wiki/UsersWikiSimplifyPreserveTopology

Nate Wessel
Jack of all trades, Master of Geography, PhD candidate in Urban Planning
NateWessel.com <http://natewessel.com>

On 1/26/19 12:31 PM, James wrote:
> it does if you saw my analysis of building(polygon count) remains the 
> same also visually inspected a few and there was preservation of them
>
> On Sat., Jan. 26, 2019, 11:43 a.m. Nate Wessel <bike756 at gmail.com 
> <mailto:bike756 at gmail.com> wrote:
>
>     Does that preserve topology between buildings that share nodes?
>
>     Nate Wessel
>     Jack of all trades, Master of Geography, PhD candidate in Urban
>     Planning
>     NateWessel.com <http://natewessel.com>
>
>     On 1/26/19 11:31 AM, James wrote:
>>     no need for scripts, qgis does this fine via the  Vector menu ->
>>     Geometry tools -> Simplify Geometries utility. I simplified it to
>>     20cm with the , but I think 40cm is too aggressive.
>>
>>     I already have scripts to compile it into the dataformat needed
>>     to be served.
>>
>>     On Sat., Jan. 26, 2019, 11:16 a.m. Nate Wessel <bike756 at gmail.com
>>     <mailto:bike756 at gmail.com> wrote:
>>
>>         Hi all,
>>
>>         The wiki page is indeed looking a whole lot better right now
>>         - my thanks and congrats to everyone who contributed! There
>>         is a still a ways to go, but we seem to be getting there
>>         quickly.
>>
>>         I'll echo John in saying that I would appreciate hearing from
>>         some of the other people who chimed in to express their
>>         doubts about the import. For my part, I'm not satisfied yet -
>>         no surprise, I'm sure ;-). I'm thrilled that we're talking
>>         and working together in the open, and that addresses the
>>         biggest concern I had with the import.
>>
>>         These are the big issues I see remaining:
>>
>>         1. *Validation*: Ideally I'd like to see a good chunk (more
>>         than half) of the data that has been imported already
>>         validated by another user before we proceed with importing
>>         more data. Validation is part of the import plan, so the
>>         import isn't done until validation is done anyway. My hope is
>>         that this will flag any issues that we can fix before moving
>>         forward, and give people time to chime in on the import plan
>>         who maybe haven't already. I don't want to see everything
>>         imported and only then do we start systematically checking
>>         the quality of our work, if ever. If no one wants to do it
>>         now, no one is going to want to do it later either, and that
>>         doesn't bode well.
>>
>>         2. *Simplification*: James' analysis showed that
>>         simplification could save several hundred megabytes (and
>>         probably more) in Ontario alone. This is totally worth doing,
>>         but we have to document the process and be very careful not
>>         to lose valuable data. I believe there was also a concern
>>         raised about orthogonal buildings being not quite orthogonal
>>         - this is something that we should handle at the same time,
>>         again, very carefully. We certainly don't want to coerce
>>         every building into right angles. With respect to James, I'm
>>         not sure this is something that can be done with a few clicks
>>         in QGIS. I would be willing to develop a script to handle
>>         this, but it would take me about a week or two to find the
>>         time to do this properly. We would need to simultaneously A)
>>         simplify straight lines B) orthogonalize where possible and
>>         C) preserve topology between connected buildings. This is not
>>         impossible, it just takes time and care to do correctly.
>>
>>         3. *Speed and Size*: To John's point, it seems like people
>>         certainly are not sticking to the areas they know, unless
>>         they get around a whole hell of a lot more than I do, and yes
>>         this is a problem. The whole Toronto region was basically
>>         imported by two people: DannyMcD seems to have done the
>>         entire west side of the region (hundreds of square
>>         kilometers) while zzptichka imported the entire east side of
>>         the region (again a truly massive area), both in the matter
>>         of a week or two. They only stopped in the middle where there
>>         were more buildings already and things got a bit more
>>         difficult. The middle is where I live, and when I saw that
>>         wave of buildings coming, I sounded the alarms.
>>         This is way too fast - no one person should be able to import
>>         the GTA in a couple weeks. A big part of the problem, IMO is
>>         that the task squares are much too large, and allow/require a
>>         user to import huge areas at once. At the least, some of the
>>         task squares in central Toronto are impossibly large,
>>         including hundreds or thousands of buildings already mapped
>>         in OSM. Conflation on these, if done properly would take the
>>         better part of a day, and people are likely to get sloppy.
>>         I would like to see the task squares dramatically reduced in
>>         size as a way of slowing people down, helping them stick to
>>         areas they know well, and keeping them focused on data
>>         quality over quantity. This would also make the process much
>>         more accessible to local mappers who don't already have tons
>>         of experience importing.
>>
>>         4. *Conflation*: I don't think the current conflation plan is
>>         adequate(ly documented). In practice, what people are
>>         actually doing may be fine, but I really want to see some
>>         better thought on how to handle existing buildings. Right now
>>         the wiki says for example "/Before merging buildings data
>>         switch to OSM layer and see if there are any clusters of
>>         buildings without any meaningful tags you can delete to save
>>         time when merging/."
>>         With respect to whoever wrote this, this approach seems to
>>         value time over data integrity and I just don't think that's
>>         how OSM should operate. We need to be more careful with the
>>         existing data, and we need to show that care with clear and
>>         acceptable guidelines for handling the data that countless
>>         people have already spent their time contributing. We don't
>>         do OSM any favours by carelessly deleting and replacing data.
>>         Help convince me that this isn't what's happening.
>>
>>         Until some effort has been made to address these concerns, I
>>         will continue to oppose this import moving forward. And to be
>>         clear, I don't want to oppose this import - I have too much
>>         else I should be focusing on. I just don't want to see
>>         another shoddy import in Toronto (or elsewhere).
>>
>>         Best,
>>
>>         Nate Wessel
>>         Jack of all trades, Master of Geography, PhD candidate in
>>         Urban Planning
>>         NateWessel.com <http://natewessel.com>
>>
>>         On 1/26/19 8:49 AM, john whelan wrote:
>>>         I'm not certain how this addresses the concerns raised by
>>>         Andrew Lester and
>>>
>>>         	Pierre Béland,
>>>
>>>         and I seem to recall one other person who expressed concerns.
>>>
>>>         I think it is important that their concerns are addressed.
>>>
>>>         Perhaps they would be kind enough to comment on whether or
>>>         not this approach addresses their concerns.
>>>
>>>         Do we have a concern that some mappers have been importing
>>>         buildings further than say twenty kilometers from where they
>>>         live?
>>>
>>>
>>>         Have you found volunteers of local mappers in
>>>         Alberta
>>>         British Columbia
>>>         Manitoba
>>>         New Brunswick
>>>         Newfoundland and Labrador
>>>         Northwest Territories
>>>         Nova Scotia
>>>         Nunavut
>>>         Ontario
>>>         Prince Edward Island
>>>         Quebec
>>>         Saskatchewan
>>>         Yukon
>>>
>>>         Who will be willing to oversee the import in each province?
>>>
>>>         Does this mean the smaller provinces may not see any data?
>>>
>>>         How will you handle cities of say 80,000 population in a
>>>         smaller province who have an interest in seeing their
>>>         buildings available but have no idea on how to contact the
>>>         provincial group?
>>>
>>>
>>>
>>>         If we go back to earlier times it was a suggestion in
>>>         talk-ca that we use the single import approach and it was
>>>         mentioned at the time there didn't seem to be a list of
>>>         local mapper groups in Canada.
>>>
>>>         I'm not saying the approach of a single import as far as the
>>>         import list and talk-ca followed by a procedure of locally
>>>         organised mappers bringing in the data is wrong I'm just
>>>         trying to ensure the project moves forward and we are in
>>>         agreement.
>>>
>>>         Thanks
>>>
>>>         Cheerio John
>>>
>>>         On Sat, 26 Jan 2019 at 00:17, OSM Volunteer stevea
>>>         <steveaOSM at softworkers.com
>>>         <mailto:steveaOSM at softworkers.com>> wrote:
>>>
>>>             Thanks to some good old-fashioned OSM collaboration,
>>>             both the
>>>             https://wiki.osm.org/wiki/Canada_Building_Import and
>>>             https://wiki.osm.org/wiki/WikiProject_Canada/Building_Canada_2020#NEWS.2C_January_2019
>>>             have been updated.  (The latter points to the former).
>>>
>>>             In short, it says there are now step-by-steps to begin
>>>             an import for a particular province, and that as the
>>>             steps get fine-tuned (they look good, but might get
>>>             minor improvements), building a community of at least
>>>             one or two mappers in each of the provinces with data
>>>             available, the Tasking Manager can and will lift the "On
>>>             Hold" or "Stopped" status.
>>>
>>>             Nice going, Canada!
>>>
>>>             See you later,
>>>
>>>             SteveA
>>>             California
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>>>
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