Can anyone recommend an efficient port to CSharp of any of the public AABB/triangle intersection algorithms.
I've been looking at Moller's approach, described abstractly here, and if I were to port it, I would probably start from this C++ version. This C++ library by Mike Vandelay seems like it could also be a great starting point.
...or... any other "wheel" that can take a triangle of Vector3's and tell me if it intersects with an AABB), relatively efficiently.
There seem to be a variety of algorithms, but most seem to be written in c++, or just described abstractly in white papers and I need a c# specific implementation for our application. Efficiency is not key, but c# is. (though efficiency is obviously nice too of course ;p )
Any C# options, before I wade through a "math" port ;) would be greatly appreciated! Thanks.
For any two convex meshes, to find whether they intersect, you need to check if there exist a separating plane. If it does, they do not intersect. The plane can be picked from any face of either shape, or the edge cross-products.
The plane is defined as a normal and an offset from Origo. So, you only have to check three faces of the AABB, and one face of the triangle.
bool IsIntersecting(IAABox box, ITriangle triangle)
{
double triangleMin, triangleMax;
double boxMin, boxMax;
// Test the box normals (x-, y- and z-axes)
var boxNormals = new IVector[] {
new Vector(1,0,0),
new Vector(0,1,0),
new Vector(0,0,1)
};
for (int i = 0; i < 3; i++)
{
IVector n = boxNormals[i];
Project(triangle.Vertices, boxNormals[i], out triangleMin, out triangleMax);
if (triangleMax < box.Start.Coords[i] || triangleMin > box.End.Coords[i])
return false; // No intersection possible.
}
// Test the triangle normal
double triangleOffset = triangle.Normal.Dot(triangle.A);
Project(box.Vertices, triangle.Normal, out boxMin, out boxMax);
if (boxMax < triangleOffset || boxMin > triangleOffset)
return false; // No intersection possible.
// Test the nine edge cross-products
IVector[] triangleEdges = new IVector[] {
triangle.A.Minus(triangle.B),
triangle.B.Minus(triangle.C),
triangle.C.Minus(triangle.A)
};
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
{
// The box normals are the same as it's edge tangents
IVector axis = triangleEdges[i].Cross(boxNormals[j]);
Project(box.Vertices, axis, out boxMin, out boxMax);
Project(triangle.Vertices, axis, out triangleMin, out triangleMax);
if (boxMax <= triangleMin || boxMin >= triangleMax)
return false; // No intersection possible
}
// No separating axis found.
return true;
}
void Project(IEnumerable<IVector> points, IVector axis,
out double min, out double max)
{
double min = double.PositiveInfinity;
double max = double.NegativeInfinity;
foreach (var p in points)
{
double val = axis.Dot(p);
if (val < min) min = val;
if (val > max) max = val;
}
}
interface IVector
{
double X { get; }
double Y { get; }
double Z { get; }
double[] Coords { get; }
double Dot(IVector other);
IVector Minus(IVector other);
IVector Cross(IVector other);
}
interface IShape
{
IEnumerable<IVector> Vertices { get; }
}
interface IAABox : IShape
{
IVector Start { get; }
IVector End { get; }
}
interface ITriangle : IShape {
IVector Normal { get; }
IVector A { get; }
IVector B { get; }
IVector C { get; }
}
A good example is the box (±10, ±10, ±10) and the triangle (12,9,9),(9,12,9),(19,19,20). None of the faces can be used as a separating plane, yet they do not intersect. The separating axis is <1,1,0>, which is obtained from the cross product between <1,0,0> and <-3,3,0>.
I noticed a small bug in this implementation which leads to false negatives.
If your triangle has one edge parallel to one axis (for example (1, 0, 0)), then you will have a null vector when computing
triangleEdges[i].Cross(boxNormals[j])
This will lead to equality in the test below and give you a false negative.
replace <= and >= by < and > at line
if (boxMax <= triangleMin || boxMin >= triangleMax)
(strict comparers to remove those cases).
Works well except for that!
Thank you
Related
I'm following Sebastian Lague's Procedural Landmass Generation tutorial . He is generating landmass' color by height value. But I want to separate landmass to a array or list as areas by their color. Because the way Sebastian use generates too many water or mountain areas so I want to make them less. I tried to edit the code of him but the code I made tooks 2-3 minutes to separate. Does anyone have idea to make it faster?
The class I use to seperate regions and the areas in every region:
public class Positions
{
public int regionID;
public int areaID;
public int x;
public float y;
public int z;
}
List<Positions> positions = new List<Positions>();
The code I try to find and list them:
for (int y = 0; y<mapChunkSize; y++)
{
for (int x = 0; x<mapChunkSize; x++)
{
float currentHeight = noiseMap[x, y];
for (int i = 0; i<regions.Length; i++)
{
if (currentHeight <= regions[i].height)
{
int areaID = 0;
if(positions.Where(x => x.regionID == i).Count() != 0)
{
areaID = getNeighourIndex(i, x, y);
}
Positions p = new Positions { regionID = i, areaID = areaID, x = x, y = noiseMap[x, y], z = y };
positions.Add(p);
break;
}
}
}
}
int getNeighourIndex(int regionID, int x, int y)
{
List<Positions> pos = positions.Where(x => x.regionID == regionID).ToList();
if (pos.Where(q => Vector2Int.Distance(new Vector2Int(q.x, q.z), new Vector2Int(x, y)) <= 1).Count() > 0)
return pos.Find(q => Vector2Int.Distance(new Vector2Int(q.x, q.z), new Vector2Int(x, y)) <= 1).areaID;
return (pos.Select(q => q.areaID).OrderBy(x => x).LastOrDefault()) + 1;
}
As always when doing optimizing, the first step should be to measure, ideally with a profiler since this can hint at what it is that takes most time.
But I would guess that the majority of the time is spent in positions.Where(x => x.regionID == regionID). To solve this you could use a multi value dictionary, i.e. a dictionary where each key can map to multiple values. It is fairly easy to make your own wrapper around a Dictionary<TKey, List<TValue>>, or you could use one from Microsoft.Experimental.Collections.
You could also consider using a hierarchical search structure for the points, like a kd-tree, quad-tree or similar.
Also, if performance is of high importance, using LINQ is likely not the best option. LINQ is convenient, but the abstraction adds some overhead. In most cases this overhead is irrelevant, but in tight loops like this it may very well be a significant factor.
I've a WPF custom panel, in which I want to layout several elements (in my case 12, but ideally I would like to find an algorithm that work for all) all with the same min width/height. The layout is a Grid, but I can choose the number of column/rows I want.
I would like to find a way to decide how many columns and how many rows I create, depending on the ratio of the window.
If the sub-elements had 1/1 ratio it would be easier; I would only have to compute the ratio for the possible layouts (admitting I've 12 sub-elements: 12/1, 6/2, 4/3, 3/4, 2/6, 1/12) and check which one is the closer to the panel width/height ratio.
But in my real case, I could set my sub-items twice as high as wide, so I'm a little bit lost on how to compute this? I guess I need to take their "ideal size", and then do some math between, but I don't know how.
Thank you!
After some experimentation and Unit Tests, I think I found a solution. In fact I don't need the width/height but just their ratio, same for elements.
I've the following class representing a Layout:
public class Layout : IEquatable<Layout>
{
public int RowCount { get; }
public int ColumnCount { get; }
public double Ratio { get; }
public Layout(int rowCount, int columnCount)
{
RowCount = rowCount;
ColumnCount = columnCount;
Ratio = (float)rowCount/columnCount;
}
}
And I've done the following to get the best layout:
public class LayoutAdapter
{
public Layout ComputeBestGridLayout(int elementsCount, double elementRatio, double panelRatio)
{
IEnumerable<Layout> possibleLayouts = GetPossibleLayouts(elementsCount);
return FindBestLayouts(possibleLayouts, elementRatio, panelRatio);
}
private IEnumerable<Layout> GetPossibleLayouts(int elementCounts)
{
//TODO Increment "elementsCounts", because maybe with some hole we will have a better match for the ratio
List<Layout> acceptedResults =new List<Layout>();
for (int i1 = 0; i1 <= elementCounts; i1++)
{
double rest2 = elementCounts%((double) i1);
if (rest2 == 0)
{
int i2 = elementCounts/i1;
acceptedResults.Add(new Layout(i1,i2));
}
}
return acceptedResults;
}
private Layout FindBestLayouts(IEnumerable<Layout> possibleLayouts, double elementRatio, double panelRatio)
{
Layout closestLayout = null;
double minDiff=Double.MaxValue;
foreach (Layout possibleLayout in possibleLayouts)
{
double currentDiff = Math.Abs((panelRatio/ elementRatio) - possibleLayout.Ratio);
if (currentDiff < minDiff)
{
minDiff = currentDiff;
closestLayout = possibleLayout;
}
}
return closestLayout;
}
}
I have a set of bounding boxes(rectangular) in a 3D space. The bounds of each box are computed and stored in a dictionary named "RegionBounds". Also, a set of points are populated in a List named "PointsToCategorize" Given a point(x,y,z) coordinates from the List populated and a bounding box to be checked in, i can check if the point is inside the box or not. The problem is, this is a big dataset. The number of points to be checked are like 1000 and the no of bounding boxes are like 250-300. So, if i loop through each bounding box for each given point; the total time it takes is like 5-6 minutes. Is there any efficient method that would do the process quicker ? If possible, a small code to do so would be great
public struct iBounds {
public double x1, x2;
public double y1, y2;
public double z1, z2;
}
public struct iPoint {
public double x,y,z
}
Dictionary<String, iBounds> RegionBounds = new Dictionary<String, iBounds>();
List<iPoint> PointsToCategorize = new List<iPoint>();
int no_of_bounding_boxes = 300;
int no_of_points_to_categorize = 1000;
for (int i = 1; i <= no_of_bounding_boxes; i++)
{
String boundingBoxName = "bound_" + i;
iBounds boundingBox = new iBounds
{
x1 = Computed By Some Other method and Formulas,
x2 = Computed By Some Other method and Formulas,
y1 = Computed By Some Other method and Formulas,
y2 = Computed By Some Other method and Formulas,
z1 = Computed By Some Other method and Formulas,
z2 = Computed By Some Other method and Formulas
};
RegionBounds.Add(boundingBoxName, boundingBox);
}
////////////Start of Output section /////////////////////////
for(int i= 1; i < = PointsToCategorize.Count; i++){
foreach(var pair in RegionBounds)
{
String myboxNmame = pair.Key;
iBounds myboxBounds = pair.Value;
Console.WriteLine(PointInside(PointsToCategorize[i],myboxBounds).ToString());
}
}
////////////// End of Output section //////////////////
private bool PointInside(iPoint mypoint, iBounds boxToBeCheckedIn)
{
if (mypoint.x > boxToBeCheckedIn.x1) && (mypoint.x < boxToBeCheckedIn.x2){
if (mypoint.y > boxToBeCheckedIn.y1) && (mypoint.y < boxToBeCheckedIn.y2){
if (mypoint.z > boxToBeCheckedIn.z1) && (mypoint.z < boxToBeCheckedIn.z2){
return true;
}
}
}else{
return false;
}
}
You may want to use a OcTree or a kD-tree data structure, which is way more efficient than iterating through all the boxes.
See also this article at the section 2-D orthogonal range searching, it has a very good resume of available techniques and algorithms, which are easily extendable to 3D
I have the following problem. I create a chart with migradoc in c#.
Suppose I have the following points for my xAxis:
20.4, 20.6, 30.6, 100.4, 200.3
The problem is that it sets every xpoint in the series on an equal distance in the chart.
While what I need is a graph who sets the xpoints on a relative distance. For example, the distance between points 20.6 and 30.6 needs to be way smaller than the distance between 30.6 and 100.4. (The points always differ, as do the number of points)
One way to make the distance good is to add extra points between the existing points. For example the first step is 0.2 extra, the second step is 10.0 extra. So I want to add for example 50 extra points between this step, so that the distance is relative the same.
This is the only thing I can come up with, can somebody give me some advice how to accomplish this? (Or another possible solution?)
This method worked out for me. I first made the distances relative:
Int64[] relAfstand = new Int64[afstand.Count()];
for(int i = 0; i < afstand.Count(); i++){
double tussenRel = Convert.ToDouble(afstand[i]);
double eindRel = Convert.ToDouble(afstand[afstand.Count()-1]);
double beginRel = Convert.ToDouble(afstand[0]);
double Rel = (((eindRel - beginRel) - (eindRel - tussenRel)) / (eindRel - beginRel));
relAfstand[i] = Convert.ToInt64((Rel)*100);
}
Then I converted the data to scale with relative with the same factor as the distances:
List<double> ConvertedData = new List<double>();
int c = 0;
int c2 = 1;
double steps = 0;
bool calcSteps = false;
bool calcDistance = false;
for (int i = 0; i < 100; i++) {
if (calcDistance == false) {
distance.Add(i);
}
if (relAfstand[c] == i) {
ConvertedData.Add(data[c]);
calcSteps = false;
c2 = 1;
c++;
}else {
if (calcSteps == false) {
steps = ((data[c] - data[c-1])/(relAfstand[c] - relAfstand[c-1]));
calcSteps = true;
}
ConvertedData.Add(data[c-1] + (steps * c2));
c2++;
}
}
calcDistance = true;
Probably not the best workaround, but it works. Since the percentages can come close together I scale both now with around 200-300 instead of 100.
I am required to create a program which reads in data from a .cvs file, and use these (x, y and z) values for a series of calculations.
I read in the file as a string, and then split this into 3 smaller strings for x, y and z.
The x, y and z coordinates represents the x and y coordinates of the contours of a lake, and the depth (z).
One of the calculations which I have to do, is to calculate the surface area of the lake, using the formula (x[i]*y[i+1])-(x[i+1]*y[i]), where z(depth) = 0.
I can get my code to run perfectly, up until the x[i+1] and y[i+1], where it keeps giving me a value of 0.
Can someone please tell me how to fix this?
Here is my code;
{
string[] ss = File.ReadAllLines(#"C:File.csv");
for (int i = 1; i < ss.Length; i++)
{
string[] valuesAsString = ss[i].Split(new char[] { ' ', ',' }, StringSplitOptions.RemoveEmptyEntries);
double[] X = new double[valuesAsString.Length];
double[] Y = new double[valuesAsString.Length];
double[] Z = new double[valuesAsString.Length];
for (int n = 0; n < 1; n++)
{
X[n] = double.Parse(valuesAsString[0]);
Y[n] = double.Parse(valuesAsString[1]);
}
do
{
double SurfaceArea = (X[n] * Y[n + 1]) - (X[n + 1] * Y[n]);
Console.WriteLine(SurfaceArea);
}
while (Z[n] == 0);
}
}
Ok, im not sure if i got it right, so you if you would take a look to what i did and tell me if its of any help.
After reviewng it a little i came up with the following:
A class for the values
public class ValueXyz
{
public double X { get; set; }
public double Y { get; set; }
public int Z { get; set; }
}
A class to manange the calculation:
public class SurfaceCalculator
{
private ValueXyz[] _valuesXyz;
private double _surface;
private readonly string _textWithValues;
public SurfaceCalculator(string textWithValues)
{
_textWithValues = textWithValues;
SetValuesToCalculate();
}
public double Surface
{
get { return _surface; }
}
public void CalculateSurface()
{
for (var i = 0; i < _valuesXyz.Length; i++)
{
if (_valuesXyz[i].Z == 0)
_surface = (_valuesXyz[i].X*_valuesXyz[i + 1].Y) - (_valuesXyz[i + 1].X*_valuesXyz[i].Y);
}
}
private void SetValuesToCalculate()
{
var valuesXyz = _textWithValues.Split(' ');
_valuesXyz = valuesXyz.Select(item => new ValueXyz
{
X = Convert.ToDouble(item.Split(',')[0]),
Y = Convert.ToDouble(item.Split(',')[1]),
Z = Convert.ToInt32(item.Split(',')[2])
}).ToArray();
}
}
So now your client code could do somethin like:
[TestMethod]
public void TestSurfaceCalculatorGetsAValue()
{
//var textWithValues = File.ReadAllText(#"C:File.csv");
var textWithValues = "424.26,424.26,0 589.43,231.46,0 720.81,14.22,1";
var calculator = new SurfaceCalculator(textWithValues);
calculator.CalculateSurface();
Assert.IsNotNull(calculator.Surface);
}
I'm not very sure i got the idea correct of how to implement the formula, but i just wanted to expose an alternative you can use, you can never have to many ways of doing one thing :).
Cheers.
By the way part of the intent i had, was not tying up your funcionality to the csv in case your source for the text in the future would change.
Step through your code in the debugger. Pay special attention to tbe behavior of the line
for (int n = 0; n < 1; n++)
This loop will execute how many times? What will the value of n be during each iteration through the loop?
Well, one thing i noticed is when you're setting your X, Y, Z vars, you're setting it to the Length of the array object instead of it's value - is that intentional?
Put a debug break on the line with:
double SurfaceArea = (X[n] * Y[n + 1]) - (X[n + 1] * Y[n]);
and check the datatype of "X", "Y" and "Z"
I've had problems in the past where it tries to calculate them as strings (because it took it out of the data source as strings). I ended up fixing it by adding CInt() to each of the variables (or Convert.ToInt32();).
Hope this helps.
As this looks like it might be a homework problem, I am trying not to give a direct solution in my answer, but I see a number of questionable parts of your code that you should examine.
Why are X, Y, Z arrays? You are creating a new array each time through the outer loop, setting the length of the array to the number of elements in the line, then only assigning a value to one element of X and Y, and never assigning Z to anything.
As phoog suggests in his answer, what is the purpose of: for (int n = 0; n < 1; n++)?
What are you trying to accomplish with the do-while loop? As it has been mentioned in the comments by Mr Skeet, X[n], Y[n], Z[n] don't exist because n does not exist outside of the loop it is declared for. Even if it did exist Z[n] will always be zero because you never assign anything to the Z array after it is initialized, so the do-while loop will run forever.