On Wed, Oct 28, 2009 at 9:19 PM, john whelan <jwhelan0...@gmail.com> wrote:
> My objective at the moment is to get something sane that can be used > by various groups in the city with GPS devices to tag trees, heritage > buildings etc. If you are saying that provided I can do a couple of > GPS traces down some of the city center roads then based on that we > can adjust the road system wholesale to more nearly agree with the GPS > as was done in Vancouver etc. then I'm more than happy. > The Yahoo! satellite imagery is pretty good for some places and I believe that Ottawa is one of those places, but I am finding that in some places it is slightly out of alignment. I do not know if it is intentional or due to some kinds of errors. The same issue was raised in Australia recently. If you can find the shift, and it may vary from one area to another, and can easily correct it then, from my perspective at least, go ahead and try. The more traces you use to set your baseline the better, and I would certainly do it in a grid pattern to ensure you are getting the proper shift. Of course if you are doing GPS traces to find the shift in the map why not use the data to correct the traces completely. And if you can encourage those that are wanting to mark specific points to also create traces and to submit them as well then you have an even better source to correct the local map. > > It's been a long time since I took a look at GIS systems > professionally and I'm not familiar with what is the best approach. I > would prefer not to put too much load on others knowing they are all > volunteers. > > I have a background in programming but its been 30 years since I was > involved in teaching computer science at university level. > > On mapping parties realistically this is better done in the spring / > summer / fall time frame when bicycles can be used, Ottawa gets a bit > chilly at this time of the year for organising something in the next > four months. > True and I have to agree with you there. But at the same time you can start to plan for one, even of you know that it will be at least four months away, and starting to tell people about it so that they can plan for it. Also having some chances to talk about exactly what you want to accomplish and how to go about doing it, such as using the editors, may help as well. Even when it is really cold people can still be making GPS tracks while they are driving, which is a pretty quick way to generate a great deal of tracks quickly, and so improve the data to correct the map, and even to make corrections all year long. > > Cheerio John > > Richard
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