With default settings in JOSM, sure. In the import I was working on, we
used a Douglas-Peucker algorithm with a 20cm threshold (before the
import started) and it worked beautifully. We had many points that
seemed to have been introduced in the shapefiles as some kind of data
artifact - they didn't add any detail to the shape at all. This
procedure removed almost all of them with no discernible reduction in
quality.
Nate Wessel
Jack of all trades, Master of Geography, PhD candidate in Urban Planning
NateWessel.com <http://natewessel.com>
On 1/18/19 4:03 PM, James wrote:
dare you to run simplify tool on anything remotely round, it will make
it look like garbage
On Fri., Jan. 18, 2019, 3:49 p.m. John Whelan <jwhelan0...@gmail.com
<mailto:jwhelan0...@gmail.com> wrote:
The import mailing list was pointed to the correct page of the
wiki. The initial post was to say this is what we were thinking of
and there was a comment saying we needed to change the comment line.
>There is no mention of this proposed import on the import catalogue
The import process was reviewed by the person who set up the
Ottawa import did we miss that step on the Ottawa import as well?
Neither was it raised as a concern on the import mailing list. I
think this is very minor and can be corrected.
We learnt a fair bit on the Ottawa import and my expectation is
since we are using experienced mappers to do the import conflation
would be either handled by them or the building not imported. We
aren't using new mappers in a mapathon here and with experienced
mappers then I think you have to trust them. The world isn't
perfect. Think in terms of service level.
>There are 2X more nodes than needed to represent the building
accurately.
The problem with correcting this is you are introducing
approximations. This will vary according to the source and this
can be simplified or corrected once its in OSM. I think this is a
different issue of a mechanical edit that needs to be considered
separately.
If we are concerned with database size then I suggest we change
the instructions to say put the source comment on the change set
rather than on the building outline.
Cheerio John
Nate Wessel wrote on 2019-01-18 3:06 PM:
John,
You seem to be playing the long game with this data - it sounds
like you've been working with this a lot longer than I have, and
you've put in the time and effort to help make this
actually-quite-incredible dataset available to us. I don't want
to stop the import from happening - quite the opposite. I just
want to make sure that the time is taken to do this right. OSM
deserves that. Your (our) long awaited victory will be the
sweeter for our patience now.
There are several specific issues I see where the I's are not
crossed, nor the t's dotted. I've mentioned several already, so
I'll try to be brief (I really need to get back to working on my
dissertation).
1) There was extremely limited discussion on the imports mailing
list. The initial email did not make clear the scope of the
project. I read the email and did not think twice at it, thinking
it was entirely about Ottawa. The link in that email was actually
to the Ottawa import, and not this one, which seems to have been
only in draft at the time.
https://lists.openstreetmap.org/pipermail/imports/2018-November/005812.html
As such, this project has NOT been reviewed by the imports list,
which is a requirement for proceeding with the import.
2) There is no mention of this proposed import on the import
catalogue (https://wiki.openstreetmap.org/wiki/Import/Catalogue)
which is required in the imports guidelines. I suspect many other
guidelines have not been followed.
3) The wiki page describing the import is not adequate to assess
the quality of the data or of the proposed import. See for
example:
https://wiki.openstreetmap.org/wiki/WikiProject_Canada/Canada_Stats_Canada_Building_Outlines_Import/Plan#Risks
The import guidelines call for a description of how conflation
will be handled. The fact that two of the major importers seem to
have a substantial disagreement about how to handle existing data
indicates this was not well discussed and I can see that it isn't
well documented.
4) The buildings need to be simplified, quite a bit actually.
Most buildings have multiple nodes representing straight lines.
This bloats the database and makes things harder to edit by hand
later. There are probably 2x more nodes than are needed to
represent the data accurately, making it harder for editors and
data consumers to work with down the road.This is a simple fix
that will save countless hours later.
... I could go on, but I think this is plenty sufficient to
justify pressing pause on all this.
Again, I don't in any way want to disrespect the work that has
gone into this effort already. We're all volunteers here and I
know how much time this all takes. However. importing all/most of
the buildings in Canada is a monstrously large task, which will
have to dance around a lot of people's toes. We should expect
this to take a really damn long time if we're going to do it
right. We need to have the patience to learn from experience,
from critique, and from the wisdom of the people who've learned
from flawed imports in the past and have devised guidelines and
processes so that we can have better experiences with this in the
future.
Nate Wessel
Jack of all trades, Master of Geography, PhD candidate in Urban
Planning
NateWessel.com <http://natewessel.com>
On 1/18/19 2:24 PM, john whelan wrote:
My background is I'm a retired civil servant who has written and
overseen procurement documents and fairly large procurements.
Dotting the is and crossing the Ts are my speciality.
There are two parts to an import. The first part is the part
played by the import mailing group. They confine themselves to
is the license correct and do you have a reasonable plan. In
this case the license is one of the few that has been confirmed
by the Legal Working Group of OpenStreetMap and as such no
questions were raised about it on the import mailing list. We
have methodology that has been used before successfully with the
Ottawa building outline import. There were major discussions
both on talk-ca and the import mailing group before that import
took place and we took note of the issues raised and addressed
them. The licensing issue goes back about eight years to when I
was talking to Federal Government Treasury Board and explaining
their Open Data license did not align with OSM. That is why
their license is now known as 2.0.
The second part is the local group makes the decision to import
they are the authority no one else.
Apparently you were not part of the talk-ca when the discussions
took place which would have been the time and place to raise
concerns.
When the Ottawa import was done there were one or two places
where the existing buildings and the import overlapped. In the
instructions on the import there are instructions to cover this.
Specifically there is a validation step. I seem to recall the
error rate was of the order of 1% and I expect this latest batch
to be roughly the same.
If you can identify which municipalities data is of poor quality
then I'm sure we can remove these. For the most part these are
from the foundation plans recorded by the municipality using
professional surveying techniques.
Would you like to clarify exactly where I failed to dot the Is
and cross the Ts please.
Many Thanks
John
On Fri, 18 Jan 2019 at 13:37, Nate Wessel <bike...@gmail.com
<mailto:bike...@gmail.com>> wrote:
Hi John,
As Steve has said, you seem to be the only one suggesting
that thousands of import committees might need to be formed.
Certainly I'm not suggesting that.
My understanding of OSM import procedure (and wiki-style
projects more generally) is that imports should operate in
an essentially consensual way where possible. The goal is to
build consent and bring people on board with a project or a
change by addressing their concerns in a meaningful and
respectful way.
I think that I have made some substantive and troubling
claims about the quality of the data being imported. I've
pointed out that this project has not followed the import
procedures that were produced by a community of mappers
larger than just those in Canada.
So to respond to your implication, I am in some sense the
one reviewing the project, just as I would welcome you to
find ways that my own contributions could be better. If you
want my credentials for reviewing your work, here they are:
1) I am an active contributor to OSM in Toronto, where I
live (and elsewhere)
2) I am currently helping to lead a building import in
Hamilton County Ohio that has better addressed some of the
issues I see this import struggling with. I can help you do
the same.
3) I've been doing research in GIS for a long time now,
though I don't need that to tell you that the issues I've
described are hardly insurmountable technically or even all
that difficult to fix. It would take maybe one day's hard
work to get the technical side of this right.
I think Canadian OSMers will agree that we can take a pause
to get things right on such a massive import. If they don't
- if I'm shouted down or better, if my critiques are
adequately addressed, then I will leave you to finish the
project in peace. I might even lend a hand if all goes well,
as I sincerely hope it does :-)
Best,
Nate Wessel
Jack of all trades, Master of Geography, PhD candidate in
Urban Planning
NateWessel.com <http://natewessel.com>
On 1/18/19 1:11 PM, john whelan wrote:
I know of no other way to contact him but he made an
interesting comment that the project is on hold in the wiki
pending review.
Would he care to comment on who is supposed to be reviewing
the project?
My understanding is that the import was raised in talk-ca
before it commenced for comment and these were generally
favourable. I took that as the local mappers to Canada had
been consulted and they are the "local mappers" authority
in this case.
I understand he has concerns about local mappers making
decisions but in Canada we have been importing similar data
through CANVEC for some time. CANVEC data comes from a
number of sources including municipal data.
Is he suggesting that each of the 3,700 municipalities in
Canada should form a group of local mappers who can make
individual decisions on whether their municipal data should
be imported and we should end up with 3,700 import plans?
Thanks John
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