[Talk-ca] part 2 of New Brunswick - NRN notes

[Sam Vekemans]

And here's part 2 (or the 1st part) of the notes, i messaged about how
OpenJUMP is used to convert, but thats really beyond the scope of my
technical ability.
Im sure someone else can help out there,

Cheers,
Sam



jsmart09's diary
*2010-02-03<http://www.openstreetmap.org/user/jsmart09/diary/9466>
*

Played with Potlatch "revert" function. Bit painful since you can't step
quickly through versions or see easily what has changed between versions
(e.g. attribute change or spatial change, or spatial but not in the area
you're zoomed in on).

Spent more time assessing accuracy. I have been using Global Mapper (GM)
v10.02 which can load and display .osm, .shp, .sid. I have overlaid OSM /
NRCan (Geobase / Canvec / whatever), SNB's 1:10k topo, SNB's SID
orthophotos. Findings, in no particular order:

- the SIDs are quite useful, very useful since a lot of the Yahoo imagery
has too coarse a resolution to resolve roads. From what I recall of the SID
technical documentation, the accuracy is supposed to be fairly good, well it
says "+/- 6.0 metres for well-defined features" here:
http://www.snb.ca/gdam-igec/e/2900e_1b_i.asp

More tech. information here: http://www.snb.ca/topo/assistance/ORE1999R.pdf.
It says 90% of well-defined features (i.e. not covered by vegetation) must
fall within 4m of their true position. Whenever I've plotted GPS positions
on these images I have been comfortable with the locations. I think I am
going to have faith in the accuracy of the SODB (Soft Copy Orthophoto
Database), as an underlay to vector data to support assessment or even for
on-screen digitizing.

Currency: imagery dates from 1996 - 2002. Obviously some roads have changed
since then but most have not.

Legality of using SNB's data: see e.g.
http://www.snb.ca/gdam-igec/e/2900e_1b_v_.asp?OrthoNum=45756660. From my
reading, it says: "do what you like with it but don't blame us if you have
problems".

- the SNB Digital Topographic Database (DTDB) has data in SHP format. This
is topo data at a nominal 1:10,000 scale. Excellent stuff but perhaps more
detailed than necessary. There are 1894 map sheets.

- the NRCan Geobase has data in SHP format on NAD83. I am interested in
roads, especially their accuracy. I am also interested in grabbing water,
forest, swamp, to supply context.

A thought I am having: it may be best in general to use Geobase roads
because the Geobase data all fits together well. Bad to use someone's hokey
GPS trace for a road and find it crossing the edge of a Geobase forest or
lake.

The Geobase roads (actually the NRN roads) seem to fit the SODB pretty well.
A problem with the NRN roads is that they are too filtered, especially at
curves: sometimes curves become too jagged and the straight segments get
noticeably far from the true curved roads.

The NRN data for NB is relatively old (2003) and does not have a great deal
of attribution. But it is pretty complete so very attractive for using.

Merging with existing OSM roads: fortunately there is not a huge amount of
roads in OSM already, for NB. This makes merging less of a problem. On the
one hand I am inclined to replace existing OSM roads with NRN ones, for
consistency and possible accuracy. On the other hand it does not seem right
to go knocking out other people's possibly good work just because "it wasn't
invented here".

For roads, it makes sense to do the main highways first starting with the
TCH. I need to find out what the preferred attribution is supposed to be for
Canada.

Water: I am attracted to the idea of doing rivers and lakes first as these
do not interfere with anyone else's work. Again I need to find out about the
preferred attribution.

Some other attributes: we should really record source, accuracy, source
date.

Tracy: looked at GPS trace + OSM road on rte 101 through Tracy. Hmm, GPS
trace seems about right but OSM road is about 70m too far E.

How can I insert images into the diary ??

Oh yes - Yahoo imagery seems a bit off sometimes in Fredericton, a few
metres, nothing drastic.

END
Posted by jsmart09 <http://www.openstreetmap.org/user/jsmart09> at Thu, 04
Feb 2010 02:49:19 +0000 in English
(English)<http://www.openstreetmap.org/diary/en>

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