**2**

# help calculating this

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#1
Members - Reputation: **103**

Posted 19 December 2012 - 12:05 PM

I attached a img with this post . Please consider the marked lines as a grid in a orthgonal projection . I want to select a tile in this grid by clicking mouse over them . i want to know what kind of a formula used to solve this kind of problem . please help me to solve this issue;Thanks in advance

john lin

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#2
Members - Reputation: **1411**

Posted 19 December 2012 - 05:59 PM

In general steps:hi to all,

I attached a img with this post . Please consider the marked lines as a grid in a orthgonal projection . I want to select a tile in this grid by clicking mouse over them . i want to know what kind of a formula used to solve this kind of problem . please help me to solve this issue;Thanks in advance

john lin

1. Multiply your world-to-view (w2v) and view-to-projection (v2p) matrices to give you a world-to-projection matrix (w2p).

2. Calculate the inverse of this to give you a projection-to-world matrix (p2w)

3. Transform the projection-space position (where you clicked on screen in projection space coordinates) to a world position

4. Transform the projection-space direction (depending on your coordinate system... something like (0, 0, 1)) to a world direction

5. Do intersection tests from the world-space point and directions to the rectangles in the grid

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#4
Members - Reputation: **346**

Posted 19 December 2012 - 06:22 PM

I'm no big expert in vision, but my first try would be to use the Canny edge detector (or some scale space variant) to create a grid image. Then partition the regions image by building a trapezoidal map. After that's done you can answer point location queries efficiently.

Though even this simple scheme will require a lot of tweaking to work correctly.

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#5
Crossbones+ - Reputation: **12841**

Posted 19 December 2012 - 08:31 PM

*“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”*

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#7
Crossbones+ - Reputation: **18617**

Posted 20 December 2012 - 03:19 PM