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Re: CRS best practices: Google Geocoding API

From: Jeremy Tandy <jeremy.tandy@gmail.com>
Date: Fri, 03 Mar 2017 16:21:06 +0000
Message-ID: <CADtUq_2Y6r+bzYDRa7Zw3uhn6yptFaVencBH92sGCOof9UnMQw@mail.gmail.com>
To: Ed Parsons <eparsons@google.com>, SDW WG Public List <public-sdw-wg@w3.org>
Fair enough.

I suppose that if we write stuff in the BP document like this, we're
documenting what is actually happening.

There's a risk that we end up encouraging people to be lazy and not bother
to think about CRS. But then, if they're in the <*rest of the world view
"that I just need to use Lat & Long - Period :-)"*>TM then they will
probably not even have considered that this is an issue in the first place.
At least this advice is consistent with geospatial data collected from the
vast majority of [consumer] devices on the planet - because they're using
GPS.

Jeremy

On Fri, 3 Mar 2017 at 16:16 Ed Parsons <eparsons@google.com> wrote:

> 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 16:21:50 UTC

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