[Talk-bd] The Kamal Ataturk Dual Carriageway

[Larry O'Neill]

Hi Guys,

This is my first descriptive document on my edits in Bangladesh, and I
certainly hope it wont be the last.
On the 7th of January, I submitted  osm.org/browse/changeset/10322877
This is my description of why and how this was done.

Dhaka has alot of dual carriageways - more than many cities I have been in.
Navigating through Dhaka will almost always involve using a dual
carriageway road at some point.
This can introduce some interesting navigational challenges, as the
physical barrier between the two carriageways imposes obvious restrictions.
In many cases in Dhaka, turning right at a junction with a DC is not an
option, left is the only way you can go.
This reality is not really reflected if the dual carriageway is mapped as a
single carriageway.
An example of this exists here: osm.org/?lat=23.76438&lon=90.37224&zoom=16
Mirpur road is marked on the map as a single carriageway, and so it is
reasonable to assume that coming from Aurangajeb Road, you can drive
straight to Lake Road, or turn right to go south on Mirpur Road.
The concrete wall would decide otherwise if you tried this, and so the map
doesnt really reflect what's on the ground.
Navigational software based on this data will trust the data, and so the
data needs to reflect the reality.

This was the case with Kamal Ataturk, and so it was changed.
The editing of it was relatively simple, but it did rely on the use of the
Bing aerial imagery, and may not be entirely correct.
The Bing imagery of Dhaka is an incredibly valuable resource
[nb: I am a JOSM user, I havent dont any of this in potlatch, any potlatch
users please feel free to reply with equivalent descriptions...]
1) open JOSM
2) go to File menu, Download from OSM. OR hit the download button on the
main toolbar. OR hit Ctrl+Shift-D
3) select the area containing the road to be edited
4) download and allow it to render the data.
5) go to Imagery menu, Bing Sat.
6) after the background image has loaded, it may need to be moved slightly.
Imagery menu, New offset.
7) use this to realign the imagery as well as you can. You may need to
match it against existing OSM data or gps traces. Click and drag on the
main editing pane.
8) hopefully the barrier between the two sides of the DC road will be
visible, click and drag the current road to one side of the barrier for its
full length. Realign or add nodes if necessary.
9) after moving the existing data to one side for the full length of the
road, click the draw nodes button on the edit toolbar, and draw in the
opposite carriageway for the full length.
10) make sure the direction of the existing way is correct, and change if
necessary [click on a way and hit r to reverse it]. Add the oneway=yes tag
to all sections of the existing way.
11) select the existing way and hit Ctrl+c to copy it. Click on your new
way and hit Ctrl+Shift-V to paste the tags. This saves a lot of time.
12) edit any junctions along the road, showing where a minor road joins
both carriageways, and where it only joins one side.
13) make sure that all possible movements at either and of the DC are
maintained
14) upload the data and you're done!

My first screenshot above shows the two junctions either side of Banani
Market, where cars can be seen turning through a gap in the wall.
The junction west of this reflects the restriction the continuous wall
imposes.
My second screenshot shows how the Gulshan end of the DC was terminated,
allowing for all possible movements.
This could have been achieved by joining all of the nodes at a single point
in the centre of Gulshan circle.
While that would have been topologically correct, and some would argue in
favor of mapping it that way, it is my personal preference to do it as
shown.
Note also in my second screenshot the poorly aligned Bing imagery. This
kind of alignment should be corrected before using it to edit.
Another thing to note is the fact that the circular road around the Gulshan
junction is cut a the two dual carriageway sections on  the south and west.
The northern and eastern roads leading out of this junction are still
incorrectly mapped as single carriageways.
After doing this once, you may find it surprisingly quick to do it for
another road in Dhaka or any other Bangladeshi town or city.

If any of my edits on the Kamal Ataturk are incorrect, have restrictions
where none exist, or would allow movement that cant be made, please feel
free to change it.
This is the beauty of collaborative and crowd sourced data - if it's wrong,
correct it and move on! =0)

I hope that the above description will be of some help to those that are
new to the OSM project, and that we will soon see more Dual Carriageways
mapped in Dhaka!
Any comments, questions, criticisms, improvements or otherwise are welcome.

Thanks
Larry
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