[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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