Provided by: libmath-planepath-perl_129-1_all 
NAME
Math::PlanePath::KochPeaks -- Koch curve peaks
SYNOPSIS
use Math::PlanePath::KochPeaks;
my $path = Math::PlanePath::KochPeaks->new;
my ($x, $y) = $path->n_to_xy (123);
DESCRIPTION
This path traces out concentric peaks made from integer versions of the self-similar "KochCurve" at
successively greater replication levels.
29 9
/ \
27----28 30----31 8
\ /
23 26 32 35 7
/ \ / \ / \
21----22 24----25 33----34 36----37 6
\ /
20 38 5
/ \
19----18 40----39 4
\ /
17 8 41 3
/ / \ \
15----16 6---- 7 9----10 42----43 2
\ \ / /
14 5 2 11 44 1
/ / / \ \ \
13 4 1 3 12 45 <- Y=0
^
-9 -8 -7 -6 -5 -4 -3 -2 -1 X=0 1 2 3 4 5 6 7 8 9 ...
The initial figure is the peak N=1,2,3 then for the next level each straight side expands to 3x longer
with a notch in the middle like N=4 through N=8,
*
/ \
*---* becomes *---* *---*
The angle is maintained in each replacement so
*
/
*---*
\
* *
/ becomes /
* *
For example the segment N=1 to N=2 becomes N=4 to N=8, or in the next level N=5 to N=6 becomes N=17 to
N=21.
The X,Y coordinates are arranged as integers on a square grid. The result is flattened triangular
segments with diagonals at a 45 degree angle.
Unlike other triangular grid paths "KochPeaks" uses the "odd" squares, with one of X,Y odd and the other
even. This means the rotation formulas etc described in "Triangular Lattice" in Math::PlanePath don't
apply directly.
Level Ranges
Counting the innermost N=1 to N=3 peak as level 0, each peak is
Nstart = level + (2*4^level + 1)/3
Nend = level + (8*4^level + 1)/3
points = Nend-Nstart+1 = 2*4^level + 1
For example the outer peak shown above is level 2 starting at Nstart=2+(2*4^2+1)/3=13 through to
Nend=2+(8*4^2+1)/3=45 with points=2*4^2+1=33 inclusive (45-13+1=33). The X width at a given level is the
endpoints at
Xlo = -(3^level)
Xhi = +(3^level)
For example the level 2 above runs from Xlo=-9 to Xhi=+9. The highest Y is the centre peak half-way
through the level at
Ypeak = 3^level
Npeak = level + (5*4^level + 1)/3
For example the level 2 outer peak above is Ypeak=3^2=9 at N=2+(5*4^2+1)/3=29. For each level the
Xlo,Xhi and Ypeak extents grow by a factor of 3.
The triangular notches in each segment are not big enough to go past the Xlo and Xhi end points. The new
triangular part can equal the ends, such as N=6 or N=19, but not go beyond.
In general a segment like N=5 to N=6 which is at the Xlo end will expand to give two such segments and
two points at the limit in the next level, as for example N=5 to N=6 expands to N=19,20 and N=20,21. So
the count of points at Xlo doubles each time,
CountLo = 2^level
CountHi = 2^level same at Xhi
FUNCTIONS
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
"$path = Math::PlanePath::KochPeaks->new ()"
Create and return a new path object.
"($x,$y) = $path->n_to_xy ($n)"
Return the X,Y coordinates of point number $n on the path. Points begin at 0 and if "$n < 0" then
the return is an empty list.
Fractional $n gives an X,Y position along a straight line between the integer positions.
Level Methods
"($n_lo, $n_hi) = $path->level_to_n_range($level)"
Return per "Level Ranges" above,
((2 * 4**$level + 1)/3 + $level,
(8 * 4**$level + 1)/3 + $level)
FORMULAS
Rectangle to N Range
The baseline for a given level is along a diagonal X+Y=3^level or -X+Y=3^level. The containing level can
thus be found as
level = floor(log3( Xmax + Ymax ))
with Xmax as maximum absolute value, max(abs(X))
The endpoint in a level is simply 1 before the start of the next, so
Nlast = Nstart(level+1) - 1
= (level+1) + (2*4^(level+1) + 1)/3 - 1
= level + (8*4^level + 1)/3
Using this Nlast is an over-estimate of the N range needed, but an easy calculation.
It's not too difficult to work down for an exact range, by considering which parts of the curve might
intersect a rectangle. But some backtracking and level descending is necessary because a rectangle might
extend into the empty part of a notch and so be past its baseline but not intersect any. There's plenty
of room for a rectangle to intersect nothing at all too.
SEE ALSO
Math::PlanePath, Math::PlanePath::KochCurve, Math::PlanePath::KochSnowflakes,
Math::PlanePath::PeanoCurve, Math::PlanePath::HilbertCurve
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Kevin Ryde
Math-PlanePath is free software; you can redistribute it and/or modify it under the terms of the GNU
General Public License as published by the Free Software Foundation; either version 3, or (at your
option) any later version.
Math-PlanePath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License along with Math-PlanePath. If not, see
<http://www.gnu.org/licenses/>.