Garmin China City Navigator NT 2012.20 CH (Official shifted+Venus non shifted)

**delaneyhee** · 6th June 2012, 09:40 AM

I am using Garmin Montana 650

**spijun** · 6th June 2012, 07:50 PM

Originally Posted by delaneyhee

I am using Garmin Montana 650

I think your product is not compatible with this map
[Only registered and activated users can see links. ]

syzygy · 30th June 2012, 03:36 AM

Originally Posted by tiynub

which one should be download (non shifted)?

If you have a Garmin China made GPS device/firmware or your navigation software is the Asia version of GMXT then download the official map, otherwise download the Venus map.

**emanuele0466** · 19th July 2012, 08:45 PM

Originally Posted by spijun

City Navigator China 2012.20 in Simplified Chinese

i tryed to install this

Code:

Please Login or Register to see the links

, but I cannot understand how to do it !!!!!

**catymag** · 7th June 2012, 12:47 AM

@ sygyzy
Can correct gmap3D.img ? The file is shifted too.
see this screen (Thanks digi-m .He says :in Shanghai I can confirm there are 3D buildings located on the Huangpu River. All landmarks are shifted.)
3tx3n

syzygy · 7th June 2012, 10:59 AM

Originally Posted by catymag

@ sygyzy
Can correct gmap3D.img ? The file is shifted too.

Yes, gmap3D.img is on my to-do list. I have not fully decoded its format, especially in the LBL subfile. So it will take a while before we have a corrected gmap3D.img.

**dalminator** · 7th June 2012, 06:30 AM

it works very well on my 2565RT..in China

syzygy · 9th June 2012, 08:17 AM

Originally Posted by Quarktasche10

As i understand the shifting is not static. Is there an algorithm to get the correct values or is whole china virtually tiled and there is a database with different correction values for every tile?

That's right. The shift is location dependent. Let (x, y) and (x', y') be the original and shifted coordinates respectively, then

x' = f(x, y)
y' = g(x, y)

where f and g are two un-published functions strictly controlled by the Chinese government. The shifts x'-x and y'-y oscillate like a wave in each direction. Although there are many ways to find, fit or approximate f and g, no one wants to break the law by publishing a high precision version of f and g.

**Quarktasche10** · 9th June 2012, 11:47 AM

Originally Posted by syzygy

x' = f(x, y)
y' = g(x, y)

where f and g are two un-published functions strictly controlled by the Chinese government.

Thanks so much.
So the only reason for the special chinese Chipsets in the Navs is to protect these two functions?
Harder to analyse a chip than to debug a special firmware?

**cwhlam** · 9th June 2012, 12:47 PM

Originally Posted by syzygy

That's right. The shift is location dependent. Let (x, y) and (x', y') be the original and shifted coordinates respectively, then

x' = f(x, y)
y' = g(x, y)

where f and g are two un-published functions strictly controlled by the Chinese government. The shifts x'-x and y'-y oscillate like a wave in each direction. Although there are many ways to find, fit or approximate f and g, no one wants to break the law by publishing a high precision version of f and g.

Then, is it breaking the law to use (or to have a copy of) the Venus map in China?