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Here is an open source implementation that converts from WGS84 to GJC2: https://github.com/googollee/eviltransform/blob/master/java/src/com/lbt05/EvilTransform

Here is an open source implementation that converts from WGS84 to GJC2: https://github.com/googollee/eviltransform/blob/master/java/src/com/lbt05/EvilTransform/WGSPointer.java https://github.com/googollee/eviltransform/blob/master/java/... https://github.com/googollee/eviltransform/blob/master/java/src/com/lbt05/EvilTransform/TransformUtil.java https://github.com/googollee/eviltransform/blob/master/java/... And converting the other way by a kind of binary search, I guess using a flaw in the obfuscation: https://github.com/googollee/eviltransform/blob/master/java/src/com/lbt05/EvilTransform/GCJPointer.java https://github.com/googollee/eviltransform/blob/master/java/... All seems very silly by today standards and I would think it hardly made sense back in 2002 when this was apparently devised.

_xnmw 2y ago
Maybe GJC2 can be modified on the fly, by changing offset parameters? So in a hypothetical war situation, only providers obtaining data in realtime from "authorized" sources would have access to accurate targeting information.
- throwaway4good 2y ago
  Not unless you want to change all the map data.
- TechnicalVault 2y ago
  Nah, because the thing is the Russian and US militaries will have their own maps of China anyway. There's a reason the UK's mapping agency retains the historic name of the Ordinance Survey, maps has always been a military thing and they've always retained surveyors.
  - jhbadger 2y ago
    This reminds me of a fascinating book titled "The Red Atlas" by John Davies and Alexander Kent which is about the very detailed maps of Western cities the Soviet Union created during the Cold War.
jillesvangurp 2y ago
As a means to keep detailed maps out of the hands of an enemy it's indeed not great. As it's all rather obvious to reverse engineer this and people have indeed done so. But as a means to force foreign companies to use Chinese data suppliers this works perfectly. Because using this software would be illegal in China and anyone looking to business there legally would end up having to use Chinese data centers, Chinese data suppliers, Chinese infrastructure, etc.
- throwaway4good 2y ago
  Some elaborate technical trade barrier? I think that is giving them too much credit. This is thinking from a military apparatus stuck in the 1950es.
  - red_trumpet 2y ago
    Maybe not planned as a barrier, but effectively being one now? So this could be a reason why not to revert it.
    - throwaway4good 2y ago
      Once you make something a standard it is hard to get rid of it even if there is an obvious better approach. Mapping is explicitly regulated so no need for an indirect barrier. AFAIK it is the same other places. If a Chinese company wanted to do an extensive commercial map of the US it would face all sorts of regulative hurdles.
  - masklinn 2y ago
    > Some elaborate technical trade barrier? I think that is giving them too much credit. One-way knowledge flows is an ubiquitous and consistent facet of china's commercial policies.
  - nikisweeting 2y ago
    > Promote the development of surveying and mapping in the service of national economic construction. It was very transparently an economic and technical development policy from the start, it was never intended as a military policy to hinder enemy mapping ability. They do similar information control across many other industries besides maps. The CCP is very good at gatekeeping access to foreign/uncensored information through a few state-owned enterprises, then metering it out as they see fit for economic progress.

_xnmw 2y ago

Maybe GJC2 can be modified on the fly, by changing offset parameters? So in a hypothetical war situation, only providers obtaining data in realtime from "authorized" sources would have access to accurate targeting information.

throwaway4good 2y ago
Not unless you want to change all the map data.
TechnicalVault 2y ago
Nah, because the thing is the Russian and US militaries will have their own maps of China anyway. There's a reason the UK's mapping agency retains the historic name of the Ordinance Survey, maps has always been a military thing and they've always retained surveyors.
- jhbadger 2y ago
  This reminds me of a fascinating book titled "The Red Atlas" by John Davies and Alexander Kent which is about the very detailed maps of Western cities the Soviet Union created during the Cold War.

jillesvangurp 2y ago

As a means to keep detailed maps out of the hands of an enemy it's indeed not great. As it's all rather obvious to reverse engineer this and people have indeed done so. But as a means to force foreign companies to use Chinese data suppliers this works perfectly. Because using this software would be illegal in China and anyone looking to business there legally would end up having to use Chinese data centers, Chinese data suppliers, Chinese infrastructure, etc.

throwaway4good 2y ago
Some elaborate technical trade barrier? I think that is giving them too much credit. This is thinking from a military apparatus stuck in the 1950es.
- red_trumpet 2y ago
  Maybe not planned as a barrier, but effectively being one now? So this could be a reason why not to revert it.
  - throwaway4good 2y ago
    Once you make something a standard it is hard to get rid of it even if there is an obvious better approach. Mapping is explicitly regulated so no need for an indirect barrier. AFAIK it is the same other places. If a Chinese company wanted to do an extensive commercial map of the US it would face all sorts of regulative hurdles.
- masklinn 2y ago
  > Some elaborate technical trade barrier? I think that is giving them too much credit. One-way knowledge flows is an ubiquitous and consistent facet of china's commercial policies.
- nikisweeting 2y ago
  > Promote the development of surveying and mapping in the service of national economic construction. It was very transparently an economic and technical development policy from the start, it was never intended as a military policy to hinder enemy mapping ability. They do similar information control across many other industries besides maps. The CCP is very good at gatekeeping access to foreign/uncensored information through a few state-owned enterprises, then metering it out as they see fit for economic progress.