[Talk-gb-westmidlands] Personal Survey Points

[Big Fat Frog]

Thanks for that.

I was aware of the survey_point tag but have only used it on officially 
recognised survey points, ie OS triangulation pillars.  I don't feel 
comfortable using that tag against any of my own measurments due to the 
low confidence levels of their accuracy.  What I was after was a 
standard way of recording the measurement of the location of a mundane 
object, such as a stile or bench as a reference point for future checking.

I feel there is a danger of becomin too reliant on imagery to make maps. 
  Most of the imagery we have was taken from low level planes not 
satelites and so some tiles were produced at an angle not directly above 
and so features are elongated etc. I know imagery is then corrected for 
this but it is not a brilliant way of doing it.  I would like to have 
set points around the map, that are user contributed that are easy to 
identify on imagery, in a good location for gps fixes and that have 
other corroborating sources of location so we can use them as our own 
trigpoints.

One way would be to identify somewhere elevated, in the open that people 
can go to and take measurements from then upload their location to osm, 
they shouldn't move the item on OSM just add their own points, with 
details of how and when they surveyed it. This way we can build up our 
own network of trig points to verify imagery against.

Jon

On 26/05/2012 16:21, rob.j.nickerson at gmail.com wrote:
> For recording trig points in OSM you can use [1], but there is nothing
> to stop someone moving the location of the node (e.g. to line up with
> aerial imagery). Do we know how accurate trig points are? If you feel
> this page needs expanding, feel free to send comments to this mailing list.
>
> As for GPS surveys, accuracy varies day to day and can deteriorate in
> built up areas (where line of sight to satellite is reduced and the
> chance of signals being reflected of buildings is increased). Unless you
> have a very strong reason to believe the aerial imagery is misaligned, I
> would be tempted to base your mapping on that.
>
> [1] http://wiki.openstreetmap.org/wiki/Survey_point
>
> Regards,
> RobJN
>
>
>
>
> On , Philip Barnes <phil at trigpoint.me.uk> wrote:
>  > On Fri, 2012-05-25 at 15:50 +0100, Big Fat Frog wrote:
>  >
>  > > Thanks Gregory and Andy for your feedback.  You're right, next day
> I got
>  >
>  > > a different result but only about 2 or 3 metres out.
>  >
>  > >
>  >
>  > > I long been convinced that the arial imagery is out and I've read as
>  >
>  > > such elsewhere but if I use an offset then my changes are at odds with
>  >
>  > > the the bulk of what others have done.
>  >
>  > >
>  >
>  > > So which is the yardstick?  Imagery, accurate survey points or
> something
>  >
>  > > else? Also, if you beleive you have a hyper accurate surevy point, then
>  >
>  > > shouldn't that be uploaded to OSM?
>  >
>  >
>  >
>  > +1
>  >
>  > I think they should. Am not certain if there are tags for things like
>  >
>  > benchmarks and trigpoints, but there really should be.
>  >
>  > http://en.wikipedia.org/wiki/Benchmark_%28surveying%29
>  >
>  >
>  >
>  > My first post in Talk-West-Midlands, I tend to follow the group but as I
>  >
>  > am based in deepest darkest Shropshire, the meet ups tend to be a bit
>  >
>  > far away.
>  >
>  >
>  >
>  > Phil (trig222)
>  >
>  >
>  >
>  >
>  >
>  >
>  >
>  > _______________________________________________
>  >
>  > Talk-gb-westmidlands mailing list
>  >
>  > Talk-gb-westmidlands at openstreetmap.org
>  >
>  > http://lists.openstreetmap.org/listinfo/talk-gb-westmidlands
>  >
>  >
>
>
> _______________________________________________
> Talk-gb-westmidlands mailing list
> Talk-gb-westmidlands at openstreetmap.org
> http://lists.openstreetmap.org/listinfo/talk-gb-westmidlands