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July 16, 2003

GPS is accurate, but map info is not?

In Shibuya, looking over Shibuya StationI just bought au's A5401CA cell phone with digicam. The good thing is that it can attach location info to photos via au's GPS functionality. Cool.

Here is a moblogged pic taken at Shibuya, Tokyo, with location info. The cell phone automatically attaches the map info, but there is a finding re: the location info. Given the geographic position such as longitude, the location is displayed at different points depending on maps. Here are samples.

Very accurateThis map info looks very accurate. Error is only some ten yards, proving that the cell phone gave me that the location info is "Grade A" out of three grades (meaning the cell phone gets highly trustful data).

Mapion's info. Position shown is far from the location!But I am familiar with Mapion's online maps, so wanted to show the map of Mapion using given geographic postioning data. Surprisingly, the position shown in Mapion's map (left) is very different from au's one. Error seems some 500 yards.

After I blogged this phenomenon in Japanese, good comments were posted. Here is a summary: There are two types of geodetic standards and location info by GPS cell phones is based upon the global geodetic standard. The government started adopting the global standard since April 2002, but some map services in Japan are still based upon the domestic (Japanese) standard. There are about 500 yard difference in locations b/w by the glocal standard and the domestic one.

Posted by Nob at 08:22 AM in Blogging, English, Moblogging, Technology |

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Listed below are links to weblogs that reference GPS is accurate, but map info is not?:

» Japanese GPS data accuracy from Live from Tokyo: Tech Blog
Nob Seki who I met at the International Moblogging Conference writes about the accuracy of the Japanese GPS data and... [Read More]

Tracked on September 08, 2003 at 10:29 AM

» GPS coordinates with my pictures from DE-duce
So I managed (with the help of Raphael and Beckett) to have my gallery check if there are GPS coordinates in my captions. [Read More]

Tracked on September 30, 2003 at 08:53 PM

Comments

so Mapion and Mapfan are still using the Tokyo Datum instead of the more universal WGS84... Now i understand... I had the same problem... I had found 450 meters difference (about 500 yards).
after looking at this page though, the map seems to show that it might actually be that Navi still uses the Tokyo Datum...
http://www.flyflickers.com/ff/gomain.htm?articles/effs/datums.htm
have a look and tell me what you think...

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