random number question

hi David,

I'm trying to write a component that will generate random spheres within a box. But the random method seems to only generate random number within certain number range so I end up with spheres that only cluster as certain region within my box. Am I not using the random method properly? The following is my code. Thanks!

Dim locPts As New List(Of Point3d)

Dim sps As New List(Of Sphere)

Dim bbox As BoundingBox

bbox = box01.BoundingBox

Dim rad As Double = 2

Dim rndx As Random

Dim rndy As Random

Dim rndz As Random

For i As Integer = 0 To fc Step 1

rndx = New Random(i * 1)

rndy = New Random(i * 2)

rndz = New random(i * 5)

Dim locPt As New Point3d(rndx.Next(bbox.Min.X + rad, bbox.Max.X - rad), rndy.Next(bbox.Min.Y + rad, bbox.Max.Y - rad), rndz.Next(bbox.Min.Z + rad, bbox.Max.Z - rad))

Dim sp01 As New Sphere(locPt, rad)

sps.Add(sp01)

A = sps

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Replies to This Discussion

Permalink Reply by Damien Alomar on September 16, 2010 at 8:09am

Your using the Next method, which is fine, but only returns integers not doubles. I'm not sure if this really explains the issue your having, but this is the only thing that I see wrong. Here's how I'd rewrite the point generation...



Dim locPt as new Point3d ((rndx.NextDouble() * (bbox.Max.X - bbox.Min.X - 4))+ bbox.Min.X + 2), _

(rndy.NextDouble() * (bbox.Max.Y - bbox.Min.Y - 4))+ bbox.Min.Y + 2), _

(rndz.NextDouble() * (bbox.Max.Z - bbox.Min.Z - 4))+ bbox.Min.Z + 2))

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Permalink Reply by David Rutten on September 16, 2010 at 9:59am

I think you should only define Random once:

Dim rnd As New Random(4) 'Use a fixed seed for consistent results

For i As Integer = 0 To fc

  Dim locPt As New Point3d(rnd.Next....rnd.Next... etc. etc.)

Next

--
David Rutten
david@mcneel.com
Poprad, Slovakia