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Re: [PROGRAMMERING] B-Spline



Hej Michael

Michael Schmidt wrote:
Mon, 27 Sep 2004 22:48:01 +0200, Peter Maersk-Moller <sslug@sslug> skrev:
Hej
Jeg leder efter et stykke kode, der lader mig udregne en
B-spline-kurve .....
Jeg har kigget lidt på http://www.ibiblio.org/e-notes/Splines/Bezier.htm
men kan ikke rigtig gennemskue, hvordan

P(t) = (1-t)P01 + tP11 = (1-t)[(1-t)P0 + tP1] + t[(1-t)P1 + tP2] = (1-t)2P0 + 2(1-t)tP1 + t2P2 ,

[BEMÆRK - i anden potens er ikke gengivet rigtig her. Se webside med Quadratic Bezier spline]

Jeg kan ikke rigtig oversætte ovenstående til en funktion a'la

f(x) = ........

da jeg ikke kan se, hvordan y1 (for P1) indgår, eller også misforstår jeg
funktionen.

Funktionen er ikke f(x) men f(t) hvor t er en step variabel (oftest tid og deraf navnet t).
Hvis du anskuer dit koordinatsystem som gulvet i et danselokale er punktmængden P(t) beskrivelsen af hvor i lokalet du har været siden du startede din dans (t=0).
Så derfor har du for to dimensioner to stedfunktioner x(t) og y(t) der tilsammen udgør stedfunktionen p(t) = p(x(t);y(t)).


Håber det hjælper på forståelsen :)
-Ellers må du råbe op ;)

Ok, det hjalp. Når jeg lader 't' gennemløbe tilpas mange værdier mellem 0 og 1, ser det ud til, at jeg får en b-spline.

Tak for hjælpen.

--PMM
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