I started answering this a couple of hours ago, but as I was documenting things
I was also testing what I'd written. I'm a lot more comfortable with the FACT
that new new bing imagery around here can't be used without several different
offsets. Previously there was not much difference between zoom levels and
'height' above sea level. In-line comments are 'chronological' :)
OpenStreetmap HADW wrote:
On 9 September 2013 20:05, Lester Caine <les...@lsces.co.uk> wrote:
I'm currently playing in an area where the highest resolution imagery is
still an older view, while as I zoom out we step to newer imagery which is
some distance off from the map tracks. I'm fairly happy with the map as I
have had some older gps tracks which it follows, and I'll run over in the
morning and gather a new track as a cross reference, but are people in
general finding that these new images are out of alignment with what is
currently mapped? Can I assume that they need realigning before using them?
I find that current BIng is usually mis-allgned by two or three metres
relative to OS StreetView, which I believe is good to better than 1
metre.
I think I'm seeing considerably more than that this morning. Both z18 and z19
layers have now updated to new imagery, but z20 is still the older view. Anybody
know how to get the size of the change from iD's realignment tool? Not that iD
is usable as the new imagery is so dark you can't distinguish features. I really
need the potlatch2 'dim' feature to make these images usable!
OK - JOSM is saying 5.5 meters + depending on height ... SSW
AH - So that is how you do it in Potlatch2 ( shift + slide )
I should probably get used to josm's different hotkeys - I've currently got
three offsets set up in that.
One reason for this is parallax error, because the images aren't taken
square on to the ground (that may be because the camera is taking in
quite a large area. You can see this with building, you can end up
with a metre or more difference depending on whether you use the top
or bottom of the building. It also presumably means that alignment
changes with the height of the land.
Obviously this pass is well over from the last one, which was pretty well
aligned. There is quite a steep slope on the area I was working on last night
and I can align things to the bottom or the top of the slope ...
-1.68; -5.13 at the top
-6.92; -8.13 down the slop :)
On the the other hand, individual GPS points usually have larger error
than this. With commercial grade GPS, you probably need several hours
averaging to get down to a metre accuracy.
The S4 GPS is poor on accuracy, unless snap to road is on you end up driving
through the fields, but I have a new USB module for the tablet which is a lot
more accurate. Obviously a dedicated receiver has a better aerial and I'll take
a run up on top when I pop out to the bank later.
Work in progress ....
--
Lester Caine - G8HFL
-----------------------------
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk
Rainbow Digital Media - http://rainbowdigitalmedia.co.uk
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