Survey points etc

Posted by kucai on 30 June 2020 in English (English)

I have been registering surveyed points from the RTK gps units that I used at work. Usually, I updated those references to JOSM’s image offset database, used to be both for Bing and Maxar. Lately however, I just uploaded data for Bing only.

Part of the reason is that I found that Maxar has quite a lot skewy images despite their recentness. Their images are also at a different zoom level than Bing, so providing offsets for both Maxar and Bing seems to be pointless. Older Bings were nicer, but newer ones seems to be the same image used by Esri and Maxar, so they are equally good (or bad).

To overcome the different zoom scale of the imageries, I always defaulted to the ‘corrected’ Bing. In areas where new roads/developments can be seen only in Maxar, I will offset Maxar to Bing. I’d find a house closeby, trace it in Bing, and then move Maxar imagery to match. Hopefully, everything will remain consistent. Well, at least until new (paid/unpaid) mappers started tracing and aligning everything to Maxar that is..

I am still undecided regarding gps tracks. Quite a few issues: bad signal (resulting bad accuracy), kalmann filter, not enough traces covering x-y axis. Better than nothing though. I’d rather prefer a 10 minute averaging (or median value) gps position.


Comment from alexkemp on 30 June 2020 at 09:25

Hi kucai

This is something that I’ve struggled with also, and particularly now that we have all been in Covid-19 lockdown, and I do not even have a metres-bad GPS track to rely on. The solution that I have been relying on in the UK follows this decision matrix:

  1. The UK roads have all been imported from an accurate Ordnance Survey DB (or at least we hope that it is accurate - my own cross-reference investigations from BorderLine imports say ‘yes’, as in the common situations where a border follows a road, river or other feature it has normally matched perfectly)
  2. The English are obsessed with roundabouts, both small & large
  3. When the Borders (mentioned above) have passed through such roundabouts it has frequently been straight through the middle
  4. The roundabouts provide an excellent target when looking through imagery, much like firing an arrow (I live in Nottingham)

The upshot (pun intended) of the above is that I correct the Imagery used to the nearest roundabout that I can find. It seems to work well so far.

Comment from kucai on 30 June 2020 at 11:01

Hail our long past overlords! :)

We still inherit your bureaucracy, in that it is difficult to get any open data from the government. Sprinkle in some nervousness in the name of national security, things might stay the same in the foreseeable future.

Things are changing though. Slow and steady as they say. Cheers!

Comment from alexkemp on 30 June 2020 at 13:22

Overlords? Long past? Where on earth do you live, kucai?

You are not alone in having to fight bureaucracy. Ordnance Survey were originally a branch of the military. Now a private company, they have to be arm-wrestled for every scrap of information (and they are the sole possessors of).

To date they (and others) have been instructed by the government to provide free access to all UK-wide:

  • Postcode centroids
  • Borderline information
    (GPS for Coastline, Country & County lines)
  • Road information
    (GPS & names)

They still withhold address information.

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