Hi Wayne,
There's no surprise in the difference we all see between ortho imagery
and World imagery. It's typical.
You'll hear more from Joe Young on this as it's a frequent question he
answers when discussing orthometrically corrected imagery based upon
real ground-truthed survey data and the work done by the
photogrammetrist in wrangling with the roll, pitch, and yawl of the film
plane, aerotriangulation, bundle adjustments, etc.
World imagery accessed from ESRI, Google or from any source isn't ortho
corrected or tied to surveyed ground control. But as long as you're
aware of its shortcomings and caveats, it is sometimes useful to
georeference; i.e., manually rectify, sections of captured World imagery
predicated on known geopositional data, including ground survey data and
real ortho imagery so long as both the creator and consumer of the work
product are on notice as to the diminished positional uncertainties in
such a quasi product. This is useful, for example, when the resolution
of the ortho image is less than the uncorrected image.
Kind regards,
Kelly
--
<http://aerial.panocea.us/>
Mr. V. Kelly Bellis, ME PLS 2099 :: WQTS485
17 Union Street :: Ellsworth, ME 04605
http://aerial.panocea.us :: 1+ (207) 667-6912
On 5/20/2018 6:25 PM, Wayne Millen wrote:
>
> In ArcMap 10.5.1 I am accessing two orthoimagery basemaps from ESRI
> online--one is the World Imagery the other is one of our State
> orthoimagery datasets being hosted by ESRI online. I also have
> downloaded tiles of the state orthoimagery.
>
> I noticed that there are positional differences when comparing the two
> web map serviced layers--the image shifts about 10 feet when
> displaying one versus the other. The tile and web map versions of the
> state orthoimagery have identical positioning.
>
> I would be surprised that this would be normal to have such a
> displacement in position. What could be causing this issue and how
> would I either fix it or at least know which data set is causing the
> issue? I need to use the state ortho as it is leaf-off and a higher
> resolution but I am wondering if something may be wrong with its data.
>
> Thanks,
>
> Wayne
>
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