Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I've lifted the maths from <a href="http://community.topcoder.com/tc?module=Static&amp;d1=tutorials&amp;d2=geometry2" rel="nofollow">here</a>,</p> <p>Okay so each point has 4 "cardinal rays", a ray being a infinite line that passes between two points.</p> <pre><code>// A line in the form Ax+By=C from 2 points public struct Ray { public readonly float A; public readonly float B; public readonly float C; public Ray(PointF one, PointF two) { this.A = two.y - one.y; this.B = one.x - two.x; this.C = (this.A * one.x) + (this.B * two.x); } } </code></pre> <p>To get the cardinals we can extend <code>PointF</code></p> <pre><code>private readonly SizeF NS = new SizeF(0.0F, 1.0F); private readonly SizeF EW = new SizeF(1.0F, 0.0F); private readonly SizeF NESW = new SizeF(1.0F, 1.0F); private readonly SizeF NWSE = new SizeF(-1.0F, 1.0F); public static IEnumerable&lt;Ray&gt; GetCardinals(this PointF point) { yield return new Ray(point + NS, point - NS); yield return new Ray(point + EW, point - EW); yield return new Ray(point + NESW, point - NESW); yield return new Ray(point + NWSE, point - NWSE); } </code></pre> <p>To find the inersection of two rays we can do</p> <pre><code>static PointF Intersection(Ray one, Ray two) { var delta = (one.A * two.B) - (two.A * one.B); if (delta == 0.0F) { //Lines are parallel return PointF.Empty; } else { var x = ((two.B * one.C) - (one.B * two.C)) / delta; var y = ((one.A * two.C) - (two.A * one.C)) / delta; return new PointF(x, y); } } </code></pre> <p>So, to get the intersections for the cardinals of two points,</p> <pre><code>public static IEnumerable&lt;PointF&gt; GetCardinalIntersections( this PointF point, PointF other); { return point.GetCardianls().SelectMany(other.GetCardinals(), Intersection) .Where(i =&gt; !i.IsEmpty()); } </code></pre> <p>Which then enables,</p> <pre><code>public static IEnumerable&lt;PointF&gt; GetCardinalIntersections( this PointF point, IEnumerable&lt;PointF&gt; others); { return others.SelectMany((o) =&gt; point.GetCardinalIntersections(o)); } </code></pre> <p>We can then use this functionality like this.</p> <pre><code>var point = new PointF(1.0F, 1.0F); var others = new [] { new PointF(2.0F, 5.0F), new PointF(-13.0F, 32.0F) }; var intersections = point.GetCardinalIntersections(others); </code></pre> <p>Obviously there is lots of iteration here, I haven't compiled or tested this but since, at its nub, the maths seems fairly efficient I'm optimistic about performance.</p>
    singulars
    1. This table or related slice is empty.
    1. PODetecting light projections and intersections in 2D space using C#
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USJodrell
    1. USJodrell
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI know this is good OOP practice, but I don't think it's a good idea to create so many objects just to perform line intersection.
      singulars
      1. PO
      1. USZong
    2. CO@ZongLi is that because the performance would be slow or becuase it would use additional memory? I'm not convinced of either is significant without testing. However, I did move the instatiation of the cardinal size offsets.
      singulars
      1. PO
      1. USJodrell
    3. COI think it's just unnecessary in this case to make such distinctions such as `Ray` objects. I believe in this case the object code only serves to obfuscate the one or two equations that are actually being evaluated.
      singulars
      1. PO
      1. USZong
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload