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

[Jamie F. <j.f...@re...>]

True. I tend to think of worst cases :)

Jamie


Robert Dibley wrote:

> He could however optimise the occasions when he does the full rescan, by
> checking to see if the value you are replacing was the maximum value, in
> which case it is _possible_ but by no means certain that your max value has
> decreased.
>
> Or even, when tracking the maximum value, keep a count of how many match the
> maximum (after all you will have to scan at the outset, so can get the
> initial count there) and then if you increase the max, it becomes 1 (ie just
> the new entry) and if you replace an entry with the current max height, with
> a lower value, you can decrement the count.  If the count of max height
> entries reaches zero, then do a rescan.  Oh, and make sure if you replace an
> entry with a new one which matches the max value that you increment the
> count too.
>
> Still doesn't solve the basic problem that you have to do a rescan
> occasionally, but stops you doing it when you really don't need to.
>
> Rob
>
> -----Original Message-----
> From: Jamie Fowlston [mailto:j.f...@re...]
> Sent: 01 August 2000 11:35
> To: gda...@li...
> Subject: Re: [Algorithms] Modifying the min and max altitude in a
> heightmap
>
> Unless you maintain a list of heixels sorted by height, I'm pretty sure you
> can't do what you want. Sorry.
>
> Jamie
>
> 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.  (-:
> >
> > -Sam
> > ______________________
> > Sam McGrath
> > sa...@dn...
> > http://www.dnai.com/~sammy
> > ICQ 5151160
> >
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