Yep. The world in question is essentially
lying in the XZ ground plane familiar to all standard 3D models, whilst the grid
notation I use goes 0-30 from where 0,0 is "top left" and values increase across
or down respectively when thought of in 2D

----- Original Message -----From:Patrick BetremieuxSent:Tuesday, May 20, 2008 6:17 PMSubject:Re: [Algorithms] Rounding ProblemZc is along the world Z, right ? Your positive world Z goes along the negative Y of your grid, unlike X that goes positive to positive. Hence the reversed fraction.Patrick.

From:gdalgorithms-list-bounces@lists.sourceforge.net [mailto:gdalgorithms-list-bounces@lists.sourceforge.net]On Behalf OfPaul at HomeSent:Tuesday, May 20, 2008 10:01 AMTo:gdalgorithms-list@lists.sourceforge.netSubject:[Algorithms] Rounding ProblemGod this is driving me nuts. It should be so simple!

I have a world system whereby a grid of 31x31 in grid units is mapped over a range of real values ranging from -15.5 to +15.5

For collision detection reasons, I need a function that will basically do a mod such that when applied to my real X or Z coordinate, it tells me (as a range 0-1) how far into a grid cell I am. I would expect the routine to return 0.1 if I'm a tenth into a particular grid square.

But, whatever combinations of mod,floor,ceil,etc I've tried, when the real coord is negative, I get a 0.9 instead of a 0.1

I'm kinda looking for a float version of "&" iyswim.

Any ideas what I'm doing wrong ?==========================================RoundDown=crt floorf btw

tINT GetGridXFromWorld (tF32 WorldX)

{

return tINT(RoundDown(WorldX+15.5F));

}

tINT GetGridYFromWorld (tF32 WorldZ)

{

return tINT(RoundDown(15.5f-WorldZ));

}I would expect this function to return how far into the current square I am as a normalised "percentage". It's changed a lot but this is definitely wrong. I just can't seem to fix it!

tF32 Frac=Abs((Zc+0.5F)-RoundDown(Zc+0.5F));

Regards,

Paul Johnson.

www.rubicondev.com

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