[Talk-ca] Update on updating the Lake Huron shoreline

James A. Treacy treacy at debian.org
Wed Jun 22 22:09:52 BST 2011


Hello,
I thought I should give an update on what I have been doing with the
shoreline for Lake Huron.

In May I updated part of the Bruce Peninsula to get a feel for how to
do the workflow. The goal was to replace the PGS shoreline with the
one from canvec. When it finally got rendered it looked great, so I
then worked SW towards Sarnia, eventually getting almost to Lake St.
Clair. It got a bit tricky there due to the way some large islands are
currently entered so I decided to go back and continue E along the
Bruce.

Maybe I should have continued towards Windsor as it is much easier
than what I have started to tackle.

Eastern Georgian Bay has a huge number of islands (I hope the other
lakes have a simpler shoreline). By itself this isn't a big deal but
a large portion of them have been entered as a monstrous ~760 member
multipolygon. Additionally, the inner ways are islands in a large
lake, which is not how it should be done. There is also a PGS based
coastline. Somehow the renderer has made sense of this and renders
something that sort of works (I imagine the code for generating a
coastline is very creative).

I have started untangling the multipolygon, making the islands
coastline. At the same time, the PGS coastline is being replaced with
the one from canvec. This is slow work and I have 'only' done about
200 islands so far. It is slowed even more by the desire to have each
change set leave everything in a consistent state (ripping everything
out in a few change sets and then adding everything back would be much
faster). When done, the multipolygon containing all the islands will
be empty and will be deleted.

The end result should be a much nicer shoreline and a dataset that
will be much easier to modify. Don't expect this work to be done until
sometime in July. The scary part is that when finished less than 1/4
of one Great Lake shoreline will be done.

After that, I'll see if I have the time/energy to continue working up
towards the French River (a nice place for canoeing!).

-- 
James (Jay) Treacy
treacy at debian.org




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