I’ve been using Merkaartor on LInux for some years. Usually I import a track, zoom in, then use “download more” to download OSM for that region. But there’s a 50,000 item limit, so if I’m not zoomed in far enough, it fails.

Years ago I had read that I could get planet.osm as a default start set, but I never did. Now, when I look, it’s huge. Merkaartor can’t handle that, at least not with the amount of RAM I have. It can’t even handle all of Canada without swapping.

I see that the US is split into states, but all of Canada is one big file. Is there any easy way, preferably command-line on Linux, that would let me split out a region from the Canada OSM - one province, or a smaller area ?

On a couple of occasions I’ve noticed what I call an “eye” effect when plotting a GPS track through trees. The first time, I walked back and forth along an east-west trail and when I passed a certain spot the traces opened up, then closed again so they were superimposed, leaving a kind of eye shape in the middle. I thought it might make sense if the trees were particularly dense, but they were not - in fact, there was a small open area over a pond to the south.

Recently I noticed a similar effect in another area, this time on a north-south section of trail. Actually walking the trail, it was quite obvious that the tracks were superimposed and then opened up for a distance then became superimposed again. I made several passes and then plotted the tracks to show the direction of travel - it seems that the position of the tracks depends which way I was going. Again, there was a slightly open area to the north - the main track in along the centre of a wooded area running SE-NW, with two small paths leading north and south. The northerly one is through a less densely wooded area. The trees are deciduous, silver birch or similar, about 80ft tall with few lower branches, spaced on average maybe 15ft apart. It’s not a particulary dense wood - not at all dark and you can easily see sky between the tree tops. I tried recording more tracks later in the day, and the next day at a different time. The tracks don’t align perfectly between each group, but the eye effect is there on each occasion. These tracks are from a Garmin GLO on my hat (taking Dieterdreist’s advice). The earlier one (not shown) was with the builtin GPS in my N810 tablet)

I wondered if anyone else had seen this effect, or knew what caused it. I’m a bit perplexed by the effect of direction of travel - surely I’m not seeing a doppler effect at walking speed, and anyway GPS sets are designed to be used when moving.

… See full entry

I’m trying to improve the accuracy of the mapped features in Smoke Bluffs Park in Squamish. This is a very popular rock-climbing area with many documented and bolted routes, so I’d like to be able to use a GPS to find a particular climb. Although the bluffs themselves are mostly exposed, most of the approach trails to top and bottom are in forest, and don’t show up on the common satellite photo sites. I was using 3 different GPS sets here - a Garmin GLO bluetooth unit talking to a Nokia N810 tablet, an Asus ME173X tablet with builtin GPS, and a Nokia E71 phone with builtin GPS. I had assumed the GLO (GPS+GLONASS) would be most accurate - it is sold as a GPS, tracks more satellites and has a faster update rate. But when I checked the tracks recorded on October 11th, there are places where “going” and “returning” traces diverge, walking the same trail. I returned on October 13th to check some features, with 3 GPS sets running, and got 3 different traces. In some cases these are far enough apart that I’m no longer sure which trail I was on at the time - the trails are in some cases quite close together. At one point I tried leaving the GLO at a fixed location, and walking twice around a loop with the Asus in order to later subtract the traces and get DGPS accuracy, but this was not very successful - the corrected trace was little better than the original. I’m not sure if I would get better results from two identical units, e.g. two GLOs.

… See full entry

I was skiing at Silver Star Mountain (BC Canada) using Maemo Mapper, which downloads the OS tiles. The ski lifts were marked, and a couple of ski runs, and at higher resolution, most of the run names but not the runs themselves.

When I look with Merkaartor, I find that all the runs were added as undefined highway with "piste" attributes, but they are not being rendered to PNG tiles.

It would be nice if they were. Or is there some alternative tile URL where one can see different views into the database ? I haven't looked at how that happens, just uploaded a few roads and trails and magically they later appear :-)

I notice that the park boundary for Indian Arm Provincial Park obscures Indian Arm (the inlet) in the tile map - slightly disconcerting when sailing up the inlet as it appears that it ends some kilometers short of the actual head. I'm not sure how best to fix it so I'll leave it for wiser heads.

I wondered if there was any interest in adding marine features to OSM, or if there was a more appropriate equivalent ("openmarinechart" ??).

I have done some charting of small areas (too shallow/small to be of interest to commercial vessels) but there had been no way to share the data, or even to get it into my GPS as a map (MapDekode to Garmin, ugh!). Generally it's readings from an echosounder, hopefully corrected to Low Water by accounting for tides and transducer depth. I used manual entry, but I presume there are automatic solutions. In OSM, I guess one could add a spot depth as a point with appropriate attributes (units, datum, value)

I also wondered about generating terrain maps from GPS elevation data; there must be quite a lot of user data available now.

I stumbled across optipng (for Linux) recently, and wondered whether it would be worth running this on the OSM tiles (or rather, incorporating the algorithm into newly generated ones).

It seems to get maybe 25% size reduction on "empty" tiles (ocean, fields) but only 2-3% on "busy" urban tiles.

I just noticed a big square on the online map "flooded" at some zoom levels - it's the same colour as the river. I guess a glitch in map data; I haven't looked with an editor. Yet.

osm.org/go/WJNYaYv-

(hmm, the "use map" feature didn't seem to save anything. I'll try adding lat/long in the boxes)

I just tried the History tab on the map page for the first time. It says "zoom in to see history" OK, do that until it works. But none of the entries are anything to do with the area I'm looking at. They are all global edits such as adding Arabic and Hebrew placenames (none in my little bit of Canada), or adding hundreds of airports all over the world. OK, on page 13 or so I can see the original data imports.

It would be nice to have a filter that removed the "big" edits from the history list.

osm.org/history?bbox=-126.0079%2C49.0996%2C-125.7722%2C49.1938

I was adding some data on Helby Island (near Bamfield, see map) in Merkaartor and noticed that the Yahoo map layer is displaced about 400m to the south.

Huh; weird. I just reloaded Merkaartor twice trying to check against Google and Yahoo online maps, and now it looks OK. So I'm not sure what was going on. Yahoo's satellite resolution in that area is not very good.