We Keep Coding

Finding the closest vertex below a certain height, from a start position

I have procedurally generated Islands with lakes, its basically a 3D mesh that has points above the water line and points below it, any vertex/point below the water level is water, everything above it is solid ground.
From any point on the mesh I want to know the closest distance to this water.
What I ended up doing was creating an Array of Vector2s, the array contains all the points on the mesh that are below the water level.
Next I wish to cycle through these elements and compare them all to find the closest one to my selected point. I am using Vector2.Distance for this because I only want the distance in the XZ components and not going up/down (Y Component).
The problem is that for most points I select this works absolutely fine, giving correct results, but sometimes it doesn't take the closest water point but instead one that is further away, even though this closer water point is confirmed to be in the array of water points that are being compared to find the closest one.
here is my code:
chunk.Vertices = new Vertice[totalVertices];
for (int i = 0, z = 0; z <= chunkSizeZ; z++)
{
for (int x = 0; x <= chunkSizeX; x++, i++)
{
Vertice vert = new Vertice();
vert.index = i;
vert.position = new Vector3(chunkStartPosition.x + x,
chunkStartPosition.y,
chunkStartPosition.z + z);
vert.centerPosition = new Vector3(vert.position.x + 0.5f,
vert.position.y,
vert.position.z + 0.5f);
vert.centerPos2 = new Vector2(vert.position.x + 0.5f,
vert.position.z + 0.5f);
chunk.Vertices[i] = vert;
}
}
Here we get all the water positions:
for (int i = 0; i < totalVertices; i++)
{
if (chunk.Vertices[i].position.y > heightCorrection + tileColliderMinimumY)
{
worldVectorsClean.Add(chunk.Vertices[i].position);
worldIndexClean.Add(chunk.Vertices[i].index);
}
else
{
worldVectorsWater.Add(chunk.Vertices[i].centerPos2);
}
}
Every single tile then calls this function on the generator itself, but only AFTER the whole map and all water points are added. Because the generator keeps track of ALL waterpoints across all chunks otherwise each chunk will only compare its own waterpoints which doesn't work because water from another chunk can be closer but wont be compared to if we don't do it this way;
public float CalculateDistanceToWater(Vector2 pos)
{
var distance = 9001f;
foreach (Vector2 waterVector in worldVectorsWater)
{
var thisDistance = Vector2.Distance(pos, waterVector);
if (thisDistance < distance)
distance = thisDistance;
}
return distance;
}
Finally when we call it from
IEnumerator FindWater()
{
yield return new WaitForSeconds(Random.Range(0.8f, 2.55f));
var pos = new Vector2(transform.position.x, transform.position.z);
distanceToWater = ChunkGenerator.instance.CalculateDistanceToWater(pos);
}
Looking forward to some help on this.

Efficient line drawing in SKCanvas

I have an app that tracks a users movements and plots the points on a custom map.
I have an issue where after a period of hours the device gets very slow and eventually runs out of memory.
My question is what would be the best way to draw only the points / lines that are visible?
My drawing code is
using (var linePaint = new SKPaint())
{
linePaint.Style = SKPaintStyle.Stroke;
linePaint.Color = SKColors.White;
linePaint.StrokeJoin = SKStrokeJoin.Round;
linePaint.StrokeCap = SKStrokeCap.Round;
linePaint.StrokeWidth = lineWidth * 2f;
Point previousPoint = null;
foreach (var point in localPoints)
{
if (previousPoint == null)
{
previousPoint = point;
continue;
}
canvas.DrawLine(previousPoint.X, previousPoint.Y, point.X, point.Y,
linePaint);
previousPoint = point;
}
How can this be reduced to only drawing points in view?

Create mesh from an Object with Spatial Awareness Mesh Observer MHL2

I'm new here and also quite new at C#/Unity2019.4.14f with VS2019, MRTK V2.5.3, and Microsoft Hololens 2 programming. I would like to ask you for advice on a problem that I have not been able to solve for weeks. First of all, I would like to quickly explain what kind of problem it is. My task is to track an object that is in an examination cube with the Spatial Mesh and to represent its shape as well as possible.Explanation screen for the task description
The calculations of where the examination cube is located in space work without any problems. But for some reason, I cannot query the Spatial Awareness Mesh Observer. Anyway, no meshes seem to be present although they are visible.
Since I am at a complete loss and no one I have asked so far has been able to help me, I am publishing my code for this function below. Please bear with me, as I am still a beginner in writing code.
public void ReadAndDrawMesh(){
//Provide a list of the cube coordinates
Vector3[] CubeCoordinateList = new Vector3[24];
//Convert Local to World Coordinates
var localToWorld = transform.localToWorldMatrix;
Vector3 cubeWorldPos = Cube.transform.position; // Reading out the centre position
Vector3[] cubeVertices = Cube.GetComponent<MeshFilter>().mesh.vertices; //World coordinates?
List<Vector3> cubeWorldVertices = new List<Vector3>();
for (int i = 0; i <= (cubeVertices.Length) - 1; i++)
{
CubeCoordinateList[i] = localToWorld.MultiplyPoint3x4(cubeVertices[i]);
}
//CubeVerticies from Vector A[0] to E[4]
float normalX1 = CubeCoordinateList[4].x - CubeCoordinateList[0].x;
float normalY1 = CubeCoordinateList[4].y - CubeCoordinateList[0].y;
float normalZ1 = CubeCoordinateList[4].z - CubeCoordinateList[0].z;
float amount1 = Mathf.Sqrt((normalX1 * normalX1) + (normalY1 * normalY1) + (normalZ1 * normalZ1));
//Create a new vector
Vector3 direction1 = new Vector3(normalX1, normalY1, normalZ1);
direction1 = direction1 / amount1;
//CubeVerticies from Vector A[0] to B[2]
float normalX2 = CubeCoordinateList[2].x - CubeCoordinateList[0].x;
float normalY2 = CubeCoordinateList[2].y - CubeCoordinateList[0].y;
float normalZ2 = CubeCoordinateList[2].z - CubeCoordinateList[0].z;
float amount2 = Mathf.Sqrt((normalX2 * normalX2) + (normalY2 * normalY2) + (normalZ2 * normalZ2));
//Create a new vector
Vector3 direction2 = new Vector3(normalX2, normalY2, normalZ2);
direction2 = direction2 / amount2;
//CubeVerticies from Vector A[0] to D[3]
float normalX3 = CubeCoordinateList[3].x - CubeCoordinateList[0].x;
float normalY3 = CubeCoordinateList[3].y - CubeCoordinateList[0].y;
float normalZ3 = CubeCoordinateList[3].z - CubeCoordinateList[0].z;
float amount3 = Mathf.Sqrt((normalX3 * normalX3) + (normalY3 * normalY3) + (normalZ3 * normalZ3));
//Create a new vector
Vector3 direction3 = new Vector3(normalX3, normalY3, normalZ3);
direction3 = direction3 / amount3;
//From MRTK 2.5.3
// Use CoreServices to quickly get access to the IMixedRealitySpatialAwarenessSystem
var spatialAwarenessService = CoreServices.SpatialAwarenessSystem;
// Cast to the IMixedRealityDataProviderAccess to get access to the data providers
var dataProviderAccess = spatialAwarenessService as IMixedRealityDataProviderAccess;
var meshObserverName = "SpatialAwarenessMeshObserverProfile";
var MeshObserver = dataProviderAccess.GetDataProvider<IMixedRealitySpatialAwarenessMeshObserver>(meshObserverName);
foreach (SpatialAwarenessMeshObject meshObject in MeshObserver.Meshes.Values)
{
Vector3[] meshObjectarray = meshObject.Filter.mesh.vertices;
//Reading the Spatial Mesh of the room
foreach (Vector3 verticiesCoordinaten in meshObjectarray)
{
//List for the mesh coordinates that come out of the scalar product calculation
Vector3[] MeshPositionList = new Vector3[meshObjectarray.Length]; ;
//Determining Direction between verticiesCoordinates of MeshObject with Centre of Cube
var dir_vectorMesh = verticiesCoordinaten - cubeWorldPos;
//Calculating the scalar product of the coordinates
var result1 = Mathf.Abs(Vector3.Dot(dir_vectorMesh, direction1)) * 2;
var result2 = Mathf.Abs(Vector3.Dot(dir_vectorMesh, direction2)) * 2;
var result3 = Mathf.Abs(Vector3.Dot(dir_vectorMesh, direction3)) * 2;
// If scalar product Negative, then write it in the list
if (result1 > amount1 && result2 > amount2 && result3 > amount3)
{
MeshPositionList[meshObjectarray.Length] = verticiesCoordinaten;
}
//Creating a new visible mesh from the points in the list
Mesh mesh = new Mesh();
mesh.vertices = MeshPositionList;
mesh.Optimize();
Graphics.DrawMeshNow(mesh, Vector3.zero, Quaternion.identity);
mesh.RecalculateNormals();
}
}
}
I hope that one of you can help me and I look forward to any constructive answers. Thank you to everyone who reads this post and perhaps responds.
Thank You.

Retrieving 3D cylinder parameters to create a Bounding Box

I'm implementing a Kinect application in XNA.
I'm pretty new on 3D programming and I'd like to know how to retrieve parameters such as radius or height from a cylinder model in order to create a bounding box around it for collision detection.
My problem is that my cylinders' position and angle are syncronized with the position of the forearm of the player in the field of the Kinect and so I don't know how to define the bounding box parameters (Center Min or Max values...).
Here is the code for my bounding box creation method:
private BoundingBox CalculateBoundingBox(Model model, Matrix worldTransform)
{
// Initialize minimum and maximum corners of the bounding box to max and min values
Vector3 min = new Vector3(float.MaxValue, float.MaxValue, float.MaxValue);
Vector3 max = new Vector3(float.MinValue, float.MinValue, float.MinValue);
// For each mesh of the model
foreach (ModelMesh mesh in model.Meshes)
{
foreach (ModelMeshPart meshPart in mesh.MeshParts)
{
// Vertex buffer parameters
int vertexStride = meshPart.VertexBuffer.VertexDeclaration.VertexStride;
int vertexBufferSize = meshPart.NumVertices * vertexStride;
// Get vertex data as float
float[] vertexData = new float[vertexBufferSize / sizeof(float)];
meshPart.VertexBuffer.GetData<float>(vertexData);
// Iterate through vertices (possibly) growing bounding box, all calculations are done in world space
for (int i = 0; i < vertexBufferSize / sizeof(float); i += vertexStride / sizeof(float))
{
Vector3 transformedPosition = Vector3.Transform(new Vector3(vertexData[i], vertexData[i + 1], vertexData[i + 2]), worldTransform);
min = Vector3.Min(min, transformedPosition);
max = Vector3.Max(max, transformedPosition);
}
}
}
// Create and return bounding box
return new BoundingBox(min, max);
}
Here is the code for my collision detection method
private bool isCollisionDetected(Model m1, Model m2)
{
bool detection;
BoundingBox b1 = CalculateBoundingBox(m1);
BoundingBox b2 = CalculateBoundingBox(m2);
if (b1.Intersects(b2))
{
detection = true;
}
else
{
detection = false;
}
return detection;
}

Each time you create a transformedPosition, add it to a list<Vector3>.
Then use that list to create a BoundingBox with the built in method BoundingBox.CreateFromPoints(myListOfTransformedPositions).
That method will return the correct min and max.

ILNumerics plot a plane at specific location

I'm currently playing around with the ILNumerics API and started to plot a few points in a cube.
Then I calculated a regression plane right through those points.
Now I'd like to plot the plane in the same scene plot but only with the same size than the point cloud.
I got the paramters of the plane (a,b,c): f(x,y) = a*x + b*y + c;
I know that only z is interesting for plotting a plane but I've got no clue how pass the right coodinates to the scene so that the plane size is about the same size than the maximum and minimum area of the points.
Could you guys give me a simple example of plotting a plane and a little suggetion how to set the bounds of that plane right?
Here is what I got so far:
private void ilPanel1_Load(object sender, EventArgs e)
{
// get the X and Y bounds and calculate Z with parameters
// plot it!
var scene = new ILScene {
new ILPlotCube(twoDMode: false) {
new ILSurface( ??? ) {
}
}
};
// view angle etc
scene.First<ILPlotCube>().Rotation = Matrix4.Rotation(
new Vector3(1f, 0.23f, 1), 0.7f);
ilPanel1.Scene = scene;
}
I hope that someone can help me ...
Thanks in advance !!!

You could take the Limits of the plotcube.Plots group and derive the coords from the bounding box from it. This gives you the min and max x and y coord for the plane. Use them to get the corresponding z values by evaluating you plane equation.
Once you have x,y and z of the plane, use them with ILSurface to plot the plane.
If you need more help, I can try to add an example.
#Edit: the following Example plots a plane through 3 arbitrary points. The planes orientation and position is computed by help of a plane function zEval. Its coefficients a,b,c are computed here from the 3 (concrete) points. You will have to compute your own equation coefficients here.
The plane is realized with a surface. One might as well take the 4 coords computed in 'P' and use an ILTriangleFan and an ILLineStrip to create the plane and the border. But the surface already comes with a Fill and a Wireframe, so we take this as a quick solution.
private void ilPanel1_Load(object sender, EventArgs e) {
// 3 arbitrary points
float[,] A = new float[3, 3] {
{ 1.0f, 2.0f, 3.0f },
{ 2.0f, 2.0f, 4.0f },
{ 2.0f, -2.0f, 2.0f }
};
// construct a new plotcube and plot the points
var scene = new ILScene {
new ILPlotCube(twoDMode: false) {
new ILPoints {
Positions = A,
Size = 4,
}
}
};
// Plane equation: this is derived from the concrete example points. In your
// real world app you will have to adopt the weights a,b and c to your points.
Func<float, float, float> zEval = (x, y) => {
float a = 1, b = 0.5f, c = 1;
return a * x + b * y + c;
};
// find bounding box of the plot contents
scene.Configure();
var limits = scene.First<ILPlotCube>().Plots.Limits;
// Construct the surface / plane to draw
// The 'plane' will be a surface constructed from a 2x2 mesh only.
// The x/y coordinates of the corners / grid points of the surface are taken from
// the limits of the plots /points. The corresponding Z coordinates are computed
// by the zEval function. So we give the ILSurface constructor not only Z coordinates
// as 2x2 matrix - but an Z,X,Y Array of size 2x2x3
ILArray<float> P = ILMath.zeros<float>(2, 2, 3);
Vector3 min = limits.Min, max = limits.Max;
P[":;:;1"] = new float[,] { { min.X, min.X }, { max.X, max.X } };
P[":;:;2"] = new float[,] { { max.Y, min.Y }, { max.Y, min.Y } };
P[":;:;0"] = new float[,] {
{ zEval(min.X, max.Y) , zEval(min.X, min.Y) },
{ zEval(max.X, max.Y) , zEval(max.X, min.Y) },
};
// create the surface, make it semitransparent and modify the colormap
scene.First<ILPlotCube>().Add(new ILSurface(P) {
Alpha = 0.6f,
Colormap = Colormaps.Prism
});
// give the scene to the panel
ilPanel1.Scene = scene;
}
This would create an image similar to this one:
#Edit2: you asked, how to disable the automatic scaling of the plot cube while adding the surface:
// before adding the surface:
var plotCube = scene.First<ILPlotCube>();
plotCube.AutoScaleOnAdd = false;
Alternatively, you can set the limits of the cube manually:
plotCube.Limits.Set(min,max);
You probably will want to disable some mouse interaction as well, since they would allow the user to rescale the cube in a similar (unwanted?) way:
plotCube.AllowZoom = false; // disables the mouse wheel zoom
plotCube.MouseDoubleClick += (_,arg) => {
arg.Cancel = true; // disable the double click - resetting for the plot cube
};