gdalgorithms-list

[Algorithms] Maximum Distance Point To AABB

[Joe A. <jo...@ti...>]

Hi,

For my terrain engine texture synthesizer, I want to dynamically load the
mipmap levels only when they are needed and delete them when they are not
needed anymore.
The terrain is subdivided into little chunks which all have their own
texture. So I would like to find out the minimum and maximum Distance from a
point to the AABB enclosing the terrain chunk.

The minimum distance was easy, but how do I get the maximum distance to the
AABB?

Thanks in advance.
bye joe

Re: [Algorithms] Maximum Distance Point To AABB

[Gil G. <gg...@ma...>]

I don't see why you would need the maximum distance for a texture
synthesizer. You will always need mip levels down to 1x1, since the slope of
the polygon has an effect on the mip level used. Edge-on polygons will
always use the 1x1 mip-level.

Anyway, an overestimate of the maximum distance is just the minimum distance
plus the length of a "diagonal" of the bbox. By diagonal I mean a line
segment joining opposite corners of the bbox.
-Gil



> Hi,
>
> For my terrain engine texture synthesizer, I want to dynamically load the
> mipmap levels only when they are needed and delete them when they are not
> needed anymore.
> The terrain is subdivided into little chunks which all have their own
> texture. So I would like to find out the minimum and maximum Distance from
a
> point to the AABB enclosing the terrain chunk.
>
> The minimum distance was easy, but how do I get the maximum distance to
the
> AABB?
>
> Thanks in advance.
> bye joe
>
> _______________________________________________
> GDAlgorithms-list mailing list
> GDA...@li...
> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list

Re: [Algorithms] Maximum Distance Point To AABB

[Tom H. <to...@3d...>]

At 11:42 PM 7/31/2000 +0200, you wrote:
>Hi,
>
>For my terrain engine texture synthesizer, I want to dynamically load the
>mipmap levels only when they are needed and delete them when they are not
>needed anymore.
>The terrain is subdivided into little chunks which all have their own
>texture. So I would like to find out the minimum and maximum Distance from a
>point to the AABB enclosing the terrain chunk.
>
>The minimum distance was easy, but how do I get the maximum distance to the
>AABB?

If you know which corner of the AABB is the minimum, then the maximum is 
the corner farthest from that corner. If the nearest point is the lower 
left, then the farthest point always the upper right. You should be able to 
figure out the actual distance pretty easily. Of course depending on the 
type of checks your doing to find the minimum, you should be able to 
reverse the sense of the tests and get the maximum instead.

Tom