Re: [Algorithms] Modifying the min and max altitude in a heightmap

[Thatcher U. <tu...@tu...>]

From: Allan Bentham <A.B...@Re...>
To: <gda...@li...>
Sent: Tuesday, August 01, 2000 7:19 AM
Subject: Re: [Algorithms] Modifying the min and max altitude in a heightmap


> Why not have a lower resolution height map that simply contains the values
> of the max and min height 'hiexels' in that particular cell?
>
> That way you can more easily reject a large (depending of course on your
> chosen resolution) number of 'heixels'.
>
> You'll still have to do a complete scan of your low res map but it will be
> faster than goin through the individual 'hiexel' map.

If you take that idea to its logical extreme (i.e. give the lower-res bitmap
its own even-lower-res min/max map, etc), you end up with a hierarchy of
maps.  The mighty quadtree is an example of such a hierarchy, and it crushes
this problem.  A "linear" quadtree is probably what you want, and probably
not to the full resolution of the original heightfield, to keep the memory
costs down.  Check the list archives and/or the web for copious info.

--
Thatcher Ulrich
http://tulrich.com


> > Sam McGrath wrote:
> >
> > > This may have a simple solution, but I haven't thought of one yet...
> > >
> > > I have a heightmap of altitude values.  The heightmap is subject to
> > > modification during the course of my program.  When I load the
heightmap
> I
> > > compute the maximum and minimum values (altitudes).  During the
program,
> > if
> > > a value in heightmap that is modified goes beyond the maximum
altitude,
> I
> > > assign that value to the maximum altitude (and similarly for the
minimum
> > > altitude).
> > >
> > > However, I also want to be able to tell if the maximum value has
> _shrunk_
> > > (or if this minimum value has increased).  So far I can't think of a
> > simple
> > > way to do this other than rescanning the whole heightmap whenever a
> value
> > is
> > > modified, and clearly this is not a practical solution.
> > >
> > > Hopefully there's a nice simple method that I'm blind to, so please
> > > enlighten me if you can.  (-: