Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Mateusz Konieczny]

4. Lipiec 2018 10:16 od j...@liotier.org :


> I am concerned about the cases where a building does exist in reality, the
> shape is less than ten meters from its position, some of the shape
> overlaps the building's position on the imagery and some of the shape
> resembles some of the building. In those cases, there is some value in the
> record: approximate position and area of the building. But there is also
> the liability of having introduced a low-quality object in the database.
>




I would not hesitate to delete such objects. It may mean that countless hours 
of low-quality

mapping is gone, but it is not justification to keep such data.

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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Hartmut Holzgraefe]

On 04.07.2018 17:19, Oleksiy Muzalyev wrote:
I tried to find a similar house on the satellite imagery of Northern 
Germany but for some reason I could not find a single one. Perhaps, they 
are rare, or blend into vegetation, or do not look like houses from above.


From the overview shot at ~1:10 to 1:12 I'd say it is showing this
neighborhood on Sylt:

https://binged.it/2KFpItb

Doesn't necessarily say that the house really is in that neighborhood,
but you get an idea how low-contrast reed thatching can bee in arial images

--
hartmut

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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Oleksiy Muzalyev]

On 7/4/2018 2:58 PM, Jean-Marc Liotier wrote:

On Wed, July 4, 2018 1:47 pm, Oleksiy Muzalyev wrote:

Sometimes I myself cannot recognize on a satellite image what kind of
building it is, - a warehouse, a cowshed, a factory, etc., or how many
levels it has got. I have to look at its shadow, surroundings, roof
surface, to make a guess.

Imagery interpretation is artful indeed - it takes practice to train the
eye, but then recognizing features from elusive hints, such as a tall
structure from its shadow, becomes reflex.

This is an area where having travelled in the target area helps a lot -
with nothing but the imagery I can with near-certainty recognize most
Senegalese schools... But I'm entirely lost trying to do the same in
neighbouring Guinea !

I saw recently a film "Nord Nord Mord" [1]. In this film there is an 
ultra-modern luxury house which costs twenty million euros (actually 
almost the whole film is sort of about it). But the building has got a 
traditional thatched roof made from reeds. You can see the house and the 
roof already at 1:20 (1 minute 20 seconds) of the video.


I tried to find a similar house on the satellite imagery of Northern 
Germany but for some reason I could not find a single one. Perhaps, they 
are rare, or blend into vegetation, or do not look like houses from above.


[1] 
https://www.zdf.de/filme/der-fernsehfilm-der-woche/nord-nord-mord-124.html


Best regards,

O.



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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Wed, July 4, 2018 1:47 pm, Oleksiy Muzalyev wrote:
> Sometimes I myself cannot recognize on a satellite image what kind of
> building it is, - a warehouse, a cowshed, a factory, etc., or how many
> levels it has got. I have to look at its shadow, surroundings, roof
> surface, to make a guess.

Imagery interpretation is artful indeed - it takes practice to train the
eye, but then recognizing features from elusive hints, such as a tall
structure from its shadow, becomes reflex.

This is an area where having travelled in the target area helps a lot -
with nothing but the imagery I can with near-certainty recognize most
Senegalese schools... But I'm entirely lost trying to do the same in
neighbouring Guinea !


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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Oleksiy Muzalyev]

I do not think that in ten years automated image recognition will be 
capable to map buildings correctly. I remember that still in 70s I read 
that computer translation will replace human translators. However, half 
a century later it is still humans who translate texts, though with the 
assistance of specialized computer programs.


Sometimes I myself cannot recognize on a satellite image what kind of 
building it is, - a warehouse, a cowshed, a factory, etc., or how many 
levels it has got. I have to look at its shadow, surroundings, roof 
surface, to make a guess. I wish in future it would be possible to 
switch in an editor from the satellite imagery to the aerial low 
altitude oblique image to see a building from a different angle.


I do some experiments in this field. For example, recently I filmed this 
historical fort 
https://www.openstreetmap.org/relation/5807132#map=18/46.50897/6.07790 
from the air at low altitude from different angles. These aerial images 
can be accessed from the map in two clicks at the fort's commons category:

https://commons.wikimedia.org/wiki/Category:Fort_du_Risoux

If in future the cost of SSDs capacity drops further, perhaps it would 
be possible to store such oblique aerial images at the map (and editor) 
itself as an addition to the major satellite imagery. And then it will 
be obvious and indisputable at what kind of structure we are looking 
vertically from the space. One such 4K aerial image covers at least 4 
hectares (the approximate area of this fort).


With best regards,
Oleksiy


On 7/4/2018 10:16 AM, Jean-Marc Liotier wrote:

...
I am convinced that the immense majority of those buildings will never be
corrected. In ten years, we can expect massive campaigns of automated
image recognition to produce new building layers - but even then the
extensive conflation will be an horribly tedious job.
...




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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Frederik Ramm]

Hi,

On 04.07.2018 10:16, Jean-Marc Liotier wrote:
> And that does not even answer the question: what to do with the
> "low-quality  shape but actually exists" cases ? I am at a loss to answer
> that.

Conflate into a point maybe - by moving the outline's tags onto one of
the corner nodes and removing the other nodes? Perhaps there's already a
function for that in JOSM, or if not, it deserves to be added.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frede...@remote.org  ##  N49°00'09" E008°23'33"

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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Tue, July 3, 2018 7:20 pm, john whelan wrote:
> I think my concern is more about the 'then a miracle occurs' in the
> project plan to clean up the buildings.

Yes because, among other reasons:
- For most people, verifying is not as gratifying as creating
- Correcting entirely incorrect geometries is many ways more work than
re-creating them from scratch

I am not concerned about the most egregious cases: cars & trucks modelled
as buildings, duplicates & superposed, rubbish heaps and vague shadows as
building=yes, buildings found in old imagery... Those I delete with no
hesitation.

I am not concerned either about minor simplifications or errors such as
the shape being traced on the roof of the building rather than its base -
those I let them be and correcting them capitalizes on a good foundation.

I am concerned about the cases where a building does exist in reality, the
shape is less than ten meters from its position, some of the shape
overlaps the building's position on the imagery and some of the shape
resembles some of the building. In those cases, there is some value in the
record: approximate position and area of the building. But there is also
the liability of having introduced a low-quality object in the database.

I am convinced that the immense majority of those buildings will never be
corrected. In ten years, we can expect massive campaigns of automated
image recognition to produce new building layers - but even then the
extensive conflation will be an horribly tedious job.

Meanwhile, for areas with reliable imagery, I can imagine Maproulette
jobs: something in the spirit of "Does this building at least partially
overlap one in the imagery and does it approximately resemble the one in
the imagery ?". Those jobs could be designed at national or regional
levels - under control of the local communities. They could be a way of
systematic quality control. But maybe I'm horribly deluded about how many
people would volunteer for such a mind-numbing task. Also, looking at
buildings one at a time is very inefficient compared to panning through an
area on JOSM - but then again, JOSM-enabled contributors that might be
motivated for this are not exactly in plentiful supply either.

And that does not even answer the question: what to do with the
"low-quality  shape but actually exists" cases ? I am at a loss to answer
that.

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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Tue, July 3, 2018 3:56 pm, mohamet lamine Ndiaye wrote:
> I am Mohamet Lamine Ndiaye [..]

Nangadef, I'm happy to hear from you - it has been a long time !

> [..] I think this is the umpteenth time we talk about it

Yes, this is a pet issue of mine - I hope that one day I'll understand why
you all seem to put so much time and energy into those buildings that I'm
not happy about... But hopefully they make other people happy !

> [..] However, it should be noted that in terms of the quality of the
> images and the density of the mapping areas, the contributors find it
> difficult to distinguish the actual boundaries of the Buildings

Yes - and distinguishing between building parts and the whole buildings is
a challenge for even the keenest eye.

> [..] Nevertheless, this does not preclude the use of these data in
> large-scale and highly resilient projects for the populations.

Do you have examples of use of that data ? That would help me understand
the benefits of mapping buildings even if they are approximate.

> [..] Other things, you should know that there are neighborhoods that do
> not benefit from subdivision and non-harmonized architecture of some lots
> do not promote aesthetics.

Indeed, the less orthogonal parts of town are a great challenge. Odette
(who is currently doing an internship at my company) told me about her
experience updating the cadastre in Ngor - it was a nightmare and they had
excellent drone imagery... So for an Openstreetmap contributor with only
orbital imagery it is simply impossible to do right - which is why I
wonder: instead of that herculean effort, why not settle for a simpler
model that provides the same data at a granularity closer to what our
resources let us record with adequate quality ?

> [..] What is important for me is that we have to start with something
> and although these data are of inferior quality, they respond to
> operational needs on the ground in case of disaster

A landuse=residential with residential=* (currently values of
residential=* are mostly "rural" and "urban" but a finer-grained
nomenclature could be designed such as "sparse single family", "dense
single family", "sparse urban", "dense urban") would provide approximate
population impact calculations at a fraction of the effort and without the
side effect of producing low quality buildings. Of course, buildings offer
much better precision - but only if they are actually precise: if a
building is mapped as two rectangles and the two sheds in the courtyard
are also mapped as generic buildings, is the result less precise than the
surfacic approximation ?

Sure, quite a few contributors do excellent work - but there is currently
not enough of them available to perform the huge task with high precision
everywhere.

> if we have data released by the cadastre

If you ever get your hands on that, I will be mightily impressed by your
advocacy work... So far I failed at getting even a simple list of street
references so I find difficult to imagine the day when Senegalese and
Malian government agencies will release cadastre and geodesic network. I'm
glad that you remain optimist... And after all, before French contributors
got their hands on IGN orthophotography and vector cadastre, many of us
(including me) didn't think it was possible - and then it happened thanks
to the efforts of the optimists and stubborn among us !


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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Tue, July 3, 2018 10:46 am, Rupert Allan wrote:
>
> [..] 'some data being better than no data' [..]

Yes but, in that case, landuse combined with density and/or building type
attributes do the job more cheaply and with none of the low quality
stigma. But, of course, there may be other reasons for insisting on
building shapes.

> Building materials and standards are used to map [..]
> A simple look at OSM metrics of, say, thousands of
> grass rooves amongst tin rooves in a fire, or hundreds of mud
> walls instead of concrete in an immanent flood, really helps.
> At this point, this data directly impacts
> and/or saves thousands of lives.
>
> That's my obsession.
>
> *Rupert Allan*
> Country Manager - Uganda

While building=hut is a useful distinction that is widely recorded in
relevant locations
(https://taginfo.openstreetmap.org/tags/building=hut#map, the
building=material you seem to refer to is actually not very popular
outside of Europe
(https://taginfo.openstreetmap.org/keys/building%3Amaterial#map) - in your
country it only appears 693 times (http://overpass-turbo.eu/s/A2C)

Most of the buildings I seen in Senegal and Mali are building=yes with no
other attribute... So, for now at least, this is not a question of
building materials.


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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Andrew Hain]

Generally, of course, yes, but there was a talk by someone who had estimated 
the population of a seasonally inhabited village by mapping buildings that are 
demolished each year.

--
Andrew

From: Jean-Marc Liotier 
Sent: 02 July 2018 15:25:38
To: Vao Matua
Cc: talk@openstreetmap.org; HOT Openstreetmap
Subject: Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings 
in Africa ?

On Mon, July 2, 2018 2:59 pm, Vao Matua wrote:
> When you say "low quality" buildings, do you mean the quality of the
> polygon data or are you judging someone's home to be of low value?

The tracing of course - mud shacks and posh villas are all equal before
Openstreetmap contributors !


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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Mon, July 2, 2018 11:55 am, AMEGAYIBO Kokou ELolo wrote:
>
> The majority of these tasks were created in training workshops on
> OpenStreetMap in Bamako, quality control work is done afterwards by the
> local community normally. I share your points of view, but for training
> workshops it is our best method to channel, control the work of the
> newbies and also familiarize them with the use of the Tasking Manager.
> I am open to any contribution who can help us improving our approach.

I understand the difficulty of getting large numbers of new contributors
started with Openstreetmap - mistakes are normal and must be accepted as a
cost of growing the project. Nevertheless, I think that there are ways to
keep that cost lower.

First, and most important, I believe that quality control should not be
relegated to "done afterwards" - especially with less proficient
contributors who are most likely to make mistakes, and especially if they
are enthusiastic (it pains me to see incredible dedication in go to
waste). Quality control must be an integral part of the contribution and
that must be drilled into new contributors as early as possible. Insist on
using the JOSM Validator, have the users look at their own contributions
on Osmose... Show them how to be more responsible of their own work ! Or
course, having experienced users supervise is valuable but they are a
scarce resource and most importantly they risk infantilizing less
experienced contributors. Most of my own contributions start with looking
at Osmose, seeing a bunch of errors and I start editing there... Quality
control is a core skill for everyone, at every level of proficiency.

Second, have users. Creating data costs, maintaining it costs... Why are
we doing it ? We are doing it for users. How do we judge quality ? I am as
fond of the map as an aesthetic object as anyone here but we all agree
that we want to put our efforts to good uses - so we judge quality by the
fitness of the product for a particular use. If the data has no users, it
is dead data.  For example, as a user, I am a walker and a cyclist - I
enjoy buildings on the map as landmarks to help me navigate... That is my
personal way of judging quality - but other users may have other ways: to
some users the purpose of having buildings in Openstreetmap may just be
"there is a building here and its shape is not that important" - and maybe
those users are the majority, who knows ? So, as a producer of data, be
aware of how the data is used - that is the key to rational quality
control. That remains true if you just chose the buildings as a new
contributor training object.

Third, make sure that the most recent imagery of decent quality is used.
For the specific case of Bamako and at the current time, ESRI World is
better than Bing: https://i.imgur.com/w6YBG70.jpg - of course, this is
subject to change over time. In understand that, for lack of available
properly surveyed geodesic reference points, large numbers of users
working with multiple sources of imagery generates its own challenges (I
found that particularly frustrating in Dakar's suburbs).

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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Jean-Marc Liotier]

On Mon, July 2, 2018 2:59 pm, Vao Matua wrote:
> When you say "low quality" buildings, do you mean the quality of the
> polygon data or are you judging someone's home to be of low value?

The tracing of course - mud shacks and posh villas are all equal before
Openstreetmap contributors !


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Re: [OSM-talk] [HOT] Why the HOT obsession with low quality buildings in Africa ?

[Vao Matua]

When you say "low quality" buildings, do you mean the quality of the
polygon data or are you judging someone's home to be of low value?

On Mon, Jul 2, 2018 at 1:24 AM, Jean-Marc Liotier  wrote:

> Active in Senegal and Mali, I have noticed that changesets tagged with
> tasking-manager HOT projects produce very large numbers of buildings.
> Those buildings appear to be of very low quality. I wonder: who uses
> this data ?
>
> If it is only necessary to assess that people live there, then a
> landuse=residential is sufficient
>
> If it is necessary to count the number of dwelling units to infer
> population, then a node is sufficient (maybe along with an attribute to
> discriminate single or multi-tenancy)
>
> If the geometry is actually necessary, then I wonder if anyone is
> satisfied with those semi-random shapes that, with some optimism, may be
> identified as being in the vicinity of actual buildings (most of the
> time)
>
> Enthusiastic contributors expend an awful lot of effort in flooding the
> map with low-quality buildings. I have seen ruins, building parts,
> walls, vague shadows on the ground, rubbish heaps, market stalls, cars
> and trucks all tagged as buildings - and I'll charitably keep from
> commenting on the geometric quality of those that attempt to map actual
> buildings (and I'll leave aside the issue of HOT leads requiring the use
> of outdated imagery such as Bing instead of ESRI World in Bamako). Is it
> the most useful way to channel the energy of inexperienced contributors
> ?
>
> I often find myself wishing that HOT leads introduce them to
> Openstreetmap through Osmose quality control rather than by churning out
> buildings like demented stonemasons trying to reach their weekly quota
> of gamified task-managing !
>
> ___
> HOT mailing list
> h...@openstreetmap.org
> https://lists.openstreetmap.org/listinfo/hot
>
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