[Talk-GB] bing image alignment

Lester Caine lester at lsces.co.uk
Tue Sep 10 08:29:24 UTC 2013


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 <lester at 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
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