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# local coordinate system

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hi all, how do i map a point that is currently with reference to a global coordinate system to refer to a local coordinate system (which itself is a subset of the global coordinate system). ~ boyd

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Hmm? What are you on about?
Is it like you have a large world, but map the screen coordinates (the world is larger than the screen) differently? If so, it's just a case of adding them. So;
(0,0)                  (10000,0)+----------------------+|        (4000,2000)   ||        +--------+    ||        |        |    ||        | X      |    ||        |(80,100)|    ||        +--------+    |+----------------------+(0,8000)               (10000,0)

If the local coordinate system is located within the global one and it's local (0,0) is at the global (4000,2000), a local (80,100) [the X] will be at (4000+80,2000+100) = (4080,2100). Naturally, this can work the other way too.

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thanks for your reply!!!.....that solved most of my problem, In my case, the pt. (80,100) would be given as part of global, so, it would be something like 4080, 2100 at the start;

what if the local coordinate system is in some angle rotation with the global; do I need to rotate and then do a translation or should do translation first and then do a rotation

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| /\ |
| / \ |
| \ / |
| \/ |
|---------|

thanks,

boyd

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