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

Regards,
Paul Johnson.
www.rubicondev.com

----- Original Message -----
From: Patrick Betremieux
Sent: Tuesday, May 20, 2008 6:17 PM
Subject: Re: [Algorithms] Rounding Problem

Zc 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 Of Paul at Home
Sent: Tuesday, May 20, 2008 10:01 AM
To: gdalgorithms-list@lists.sourceforge.net
Subject: [Algorithms] Rounding Problem

God 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

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/

_______________________________________________
GDAlgorithms-list mailing list
GDAlgorithms-list@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list
Archives:
http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list