APIにおける世界測地系 - Google-Maps-API-Japan

From:  "Chris Atenasio" <atena...@google.com>
To:  "Google-Maps-API-Japan" <Google-Maps-API-Japan@googlegroups.com>
Subject: =?ISO-2022-JP?B?QVBJGyRCJEskKiQxJGtAJDMmQixDTzdPGyhC?=
Date: Wed, 09 Nov 2005 01:41:25 -0000
Message-ID: <1131500485.376475.206770@g43g2000cwa.googlegroups.com>
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    http://vldb.gsi.go.jp/sokuchi/tky2jgd/download/agreement.html

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  http://www.gsi.go.jp/LAW/G2000/g2000.htm

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Dear Maps API users,

We're ready to fix the Japan datum skew on the API, but we need your
help.  If you are using the Maps API to show maps of Japan, please
read on.

When we launched Local and Maps in Japan, all our data was in the
Tokyo geodetic datum.  A "geodetic datum" said simply defines how to
measure the latitude and longitude of a point on the earth.

Since then we've been working to accurately re-project all the bits
and pieces into the WGS84 geodetic datum - this is the one most GPS
devices read.  Once we're done, you'll be able to use the same
coordinate system internationally across Local, Maps API, Earth, not
to mention your GPS.  But this is where we need your help.

For the final step, shifting API maps, we need you to transform your
latitude/longitude points in Japan into WGS84.

To help with the transition, starting today you can switch to the new
WGS84 maps by adding the CGI parameter &datum=wgs84 to your API
javascript request:

  http://maps.google.com/maps?file=api&v=1&key=...&datum=wgs84

Don't worry, the parameter will just turn into a no-op once we make
the WGS84 default.

The best way to transform points (Tokyo datum -> WGS84) probably
depends on your situation:

- If you've been using "kjapandatumhack = false" or other javascript
  patches, you might well be able to just rip the patch out and have
  things work.

- If you have just a few points to re-project, you can probably get
  away with reading them from local.google.com(already in WGS84).
  Find and double-click the place you want to mark, hit the "Link to
  this page" text in the upper-right of the screen, and copy down the
  "ll" parameter from the URL bar.

- If you have more than just a few points, you might be interested in
  using a more industrial conversion package.  The Japan Geographical
  Survey Institute has a nice grid+software solution for converting
  Tokyo-datum coordinates to JGD2000(WGS84 +/- 10cm).  You can
  download it here:

    http://vldb.gsi.go.jp/sokuchi/tky2jgd/download/agreement.html

Also I expect there might be a few members of the API community coming
out with with even better solutions, much like they did when we
launched maps with the datum hack in the first place.

Please switch to WGS84 maps by December 1st. We will be dropping Tokyo
datum support after that to make way for new and exciting things to
come.

Finally, for a bit more on geodetic datum in general, try here:

  http://www.colorado.edu/geography/gcraft/notes/datum/datum_f.html

Thanks

chris