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Re: CRS best practices: Google Geocoding API

From: Ed Parsons <eparsons@google.com>
Date: Fri, 03 Mar 2017 16:16:22 +0000
Message-ID: <CAHrFjcmH0d20Fzc8nfuSTzR4jXsM_vkUAeqeB18fBzzG=VuGsw@mail.gmail.com>
To: Jeremy Tandy <jeremy.tandy@gmail.com>, SDW WG Public List <public-sdw-wg@w3.org>
I think the first part is OK, the vertical datum part is less common and as
a result it's more difficult to make a similar assumption.

Ed


On Fri, 3 Mar 2017 at 16:11 Jeremy Tandy <jeremy.tandy@gmail.com> wrote:

> Hmmm.
>
> schema.org documents go to the trouble of saying "WGS 84" (although they
> don't describe the units either).
>
> So (as much as most of the Geo-establishment will flame me for it) should
> we be saying:
>
> "If neither your data nor the specification to which your data conforms to
> defines the coordinate reference system used, then [it's safe to] assume
> that the data with coordinate pairs uses longitude and latitude, defined in
> decimal degrees, and data with coordinate positions that have three values
> is longitude, latitude and elevation, defined in decimal degrees, decimal
> degrees and meters above sea-level. In both cases, the WGS 84 [geodetic]
> datum is assumed."
>
> Let the barbecue begin.
>
> Jeremy
>
>
> On Fri, 3 Mar 2017 at 16:02 Ed Parsons <eparsons@google.com> wrote:
>
> I think you are experiencing the rest of the world view "that I just need
> to use Lat & Long - Period :-)"
>
> The use of WGS84 is documented here
> https://developers.google.com/maps/documentation/javascript/maptypes if
> you go looking for it, must I would argue that most mainstream web
> developers don't need to know..
>
> btw this is also quite a nice explanation of tile based spatial indices ;-)
>
> Ed
>
>
>
> On Fri, 3 Mar 2017 at 15:14 Jeremy Tandy <jeremy.tandy@gmail.com> wrote:
>
> Hi Ed- in the introductory material you wrote about CRS you make a
> reference to the Google Geocoding API [1], in that its responses explicitly
> state Lat and Long rather than a coordinate pair of ambiguous order.
>
> Lat and Long are, by definition, angular measurements. OK - got that.
>
> But parsing through the API documentation, I can't see any reference to
> the units or datum which is used.
>
> Being a human, I'm prepared to guess that these are decimal degrees
> (because they look like floating point numbers). Easy for machines to
> figure that out too.
>
> As a human, I'm also prepared to guess that the API uses the WGS84. But
> that is a tricky leap for machines to work out.
>
> Does the API documentation say "WGS84" anywhere? If so, can you point me
> to it so I can refer to this explicitly? And if not, can you either justify
> why it doesn't matter, or get your colleagues to update the documentation
> (and then send me a link!).
>
> (I think that we've all agreed that it's dangerous to _assume_ a CRS :-) )
>
> Thanks, Jeremy
>
> [1]: https://developers.google.com/maps/documentation/geocoding/intro
>
> --
>
> *Ed Parsons *FRGS
> Geospatial Technologist, Google
>
> Google Voice +44 (0)20 7881 4501
> www.edparsons.com @edparsons
>
> --

*Ed Parsons *FRGS
Geospatial Technologist, Google

Google Voice +44 (0)20 7881 4501
www.edparsons.com @edparsons
Received on Friday, 3 March 2017 16:24:08 UTC

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