I check the geo source code of Redis, and one statement I cannot understanding is double difference_longitude = asin(sin(distance) / cos(latr));
What's the asin(sin(distance) / cos(latr)) meaning? Is there any theory from the wikipedia?
http://download.redis.io/redis-stable/deps/geohash-int/geohash_helper.c
#define D_R (M_PI / 180.0)
static inline double deg_rad(double ang) { return ang * D_R; }
static inline double rad_deg(double ang) { return ang / D_R; }
int geohashBoundingBox(double longitude, double latitude, double radius_meters,
double *bounds) {
if (!bounds) return 0;
double lonr, latr;
lonr = deg_rad(longitude);
latr = deg_rad(latitude);
if (radius_meters > EARTH_RADIUS_IN_METERS)
radius_meters = EARTH_RADIUS_IN_METERS;
double distance = radius_meters / EARTH_RADIUS_IN_METERS;
double min_latitude = latr - distance;
double max_latitude = latr + distance;
/* Note: we're being lazy and not accounting for coordinates near poles */
double min_longitude, max_longitude;
**double difference_longitude = asin(sin(distance) / cos(latr));**
min_longitude = lonr - difference_longitude;
max_longitude = lonr + difference_longitude;
bounds[0] = rad_deg(min_longitude);
bounds[1] = rad_deg(min_latitude);
bounds[2] = rad_deg(max_longitude);
bounds[3] = rad_deg(max_latitude);
return 1;
}
Related
I am using lis3mdl magnetometer in my quadcopter project to compensate gyroscope drift. Unfortunatelly Im having problems probably with calibrating.
Ive achive max and min values (what is weird they are 14 bits instead of 16) and calculated biases like that :
biases[i] = (MAX_VALUES[i]+MIN_VALUES[i])/2;
(where i represent each of 3 axis).
Ive substracted biases from raw values x = (double)new_x-biases[0]; (etc), and then wanted to calculate heading like that :
heading = atan2(x,y);
heading += declinationAngle;
where declination angle is calculated.
Outcome are angles (conversion from radians heading*(180/M_PI)), and it does change when Iam rotating quad in yaw axi, BUT when I am rotating it in roll and pitch axi value change either. I want to achive stable yaw value which does not change when Iam rotating object in other axis. Maybe some type of fusing with accelerometer?
I am not sure when Ive made mistake in my calculations...
Whole class:
class Magnetometer {
int x=0,y=0,z=0;
LIS3MDL mag;
int running_min[3] = {32767, 32767, 32767}, running_max[3] = {-32768, -32768, -32768};
double mag_norm = 0.0;
double declinationAngle = 0.0;
double heading=0.0;
const int MAX_VALUES[3] = {3014,3439,10246};
const int MIN_VALUES[3] = {-4746, -4110, 492};
double biases[3] = {0.0};
double scales[3] = {0.0};
double avg_scale = 0.0;
ButterworthDLPF xyz_filter[3];
double DLPF_ON = true;
const float sample_rate = MAG_SAMPLE_RATE;
const float cutoff_freq = 4.0;
public:
Magnetometer() {}
void Init() {
declinationAngle = (6.0 + (8.0 / 60.0)) / (180.0 / M_PI);
for(int i=0; i<3; i++) {
biases[i] = (MAX_VALUES[i]+MIN_VALUES[i])/2;
scales[i] = (MAX_VALUES[i]-MIN_VALUES[i])/2;
}
avg_scale = (scales[0]+scales[1]+scales[2])/3.0;
for(int i=0; i<3; i++) scales[i] = avg_scale / scales[i];
Serial.println("Turning on magnetometer. . .");
if(!mag.init()) {
Serial.println("Failed to detect magnetometer!");
ESP.restart();
}
mag.enableDefault();
//Calibrate();
for(int i=0; i<3; i++) xyz_filter[i].Init(sample_rate, cutoff_freq);
Serial.println("9DOF readdy!");
}
void Calibrate() {
delay(100);
while(true) {
mag.read();
if(running_max[0]<mag.m.x) running_max[0] = mag.m.x;
if(running_max[1]<mag.m.y) running_max[1] = mag.m.y;
if(running_max[2]<mag.m.z) running_max[2] = mag.m.z;
if(running_min[0]>mag.m.x) running_min[0] = mag.m.x;
if(running_min[1]>mag.m.y) running_min[1] = mag.m.y;
if(running_min[2]>mag.m.z) running_min[2] = mag.m.z;
Serial.println((String)running_max[0]+" "+(String)running_max[1]+" "+(String)running_max[2]+ " "+(String)running_min[0] +" "+(String)running_min[1]+" "+(String)running_min[2]);
delay(20);
}
}
void Update(){
mag.read();
xyz_filter[0].Update(mag.m.x);
xyz_filter[1].Update(mag.m.y);
xyz_filter[2].Update(mag.m.z);
//Serial.println(xyz_filter[0].getData());
/*x = ((double)xyz_filter[0].getData()-biases[0])*scales[0];
y = ((double)xyz_filter[1].getData()-biases[1])*scales[1];
z = ((double)xyz_filter[2].getData()-biases[2])*scales[2];*/
x = ((double)mag.m.x-biases[0])*scales[0];
y = ((double)mag.m.y-biases[1])*scales[1];
z = ((double)mag.m.z-biases[2])*scales[2];
CalculateHeading();
}
void CalculateHeading() {
heading = atan2(y,x);
heading += declinationAngle;
//if(heading<0) heading += 2*PI;
//else if(heading>2*PI) heading -= 2*PI;
heading=MOD(heading*(180/M_PI));
}
double GetHeading() {return heading;}
void ShowRawValues(bool names=false) {
if(names) Serial.print("X: "+(String)x+" Y: "+ (String)y+ " Z: " + (String)z);
else Serial.print((String)x+" "+ (String)y+ " " + (String)z);
}
};
I have a more mathematical than programming question, sorry if I'm not in the right section. In my 2D game, we can move the camera on a map where there are objects that can emit sound, and this sound volume (defined by a float from 0 to 1) must increase when the screen center is near this object. For example, when the object is at the screen center, the sound volume is 1, and when we move away, the volume must decrease. Each object has its own scope value. (for example 1000 pixels).
I don't know how to write a method that can calculate it.
Here is some of my code (which is not the right calculation) :
private function setVolumeWithDistance():Void
{
sound.volume = getDistanceFromScreenCenter() / range;
// So the volume is a 0 to 1 float, the range is the scope in pixels and
// and the getDistanceFromScreenCenter() is the distance in pixels
}
I already have the method which calculates the distance of the object from the center screen :
public function getDistanceFromScreenCenter():Float
{
return Math.sqrt(Math.pow((Cameraman.getInstance().getFocusPosition().x - position.x), 2) +
Math.pow((Cameraman.getInstance().getFocusPosition().y - position.y), 2));
Simple acoustics can help.
Here is the formula for sound intensity from a point source. It follows an inverse square of distance rule. Build that into your code.
You need to consider the mapping between global and screen coordinates. You have to map pixel location on the screen to physical coordinates and back.
Your distance code is flawed. No one should use pow() to square numbers. Yours is susceptible to round off errors.
This code combines the distance calculation, done properly, and attempts to solve the inverse square intensity calculation. Note: Inverse square is singular for zero distance.
package physics;
/**
* Simple model for an acoustic point source
* Created by Michael
* Creation date 1/16/2016.
* #link https://stackoverflow.com/questions/34827629/calculate-sound-value-with-distance/34828300?noredirect=1#comment57399595_34828300
*/
public class AcousticPointSource {
// Units matter here....
private static final double DEFAULT_REFERENCE_INTENSITY = 0.01;
private static final double DEFAULT_REFERENCE_DISTANCE = 1.0;
// Units matter here...
private double referenceDistance;
private double referenceIntensity;
public static void main(String[] args) {
int numPoints = 20;
double x = 0.0;
double dx = 0.05;
AcousticPointSource source = new AcousticPointSource();
for (int i = 0; i < numPoints; ++i) {
x += dx;
Point p = new Point(x);
System.out.println(String.format("point %s intensity %-10.6f", p, source.intensity(p)));
}
}
public AcousticPointSource() {
this(DEFAULT_REFERENCE_DISTANCE, DEFAULT_REFERENCE_INTENSITY);
}
public AcousticPointSource(double referenceDistance, double referenceIntensity) {
if (referenceDistance <= 0.0) throw new IllegalArgumentException("distance must be positive");
if (referenceIntensity <= 0.0) throw new IllegalArgumentException("intensity must be positive");
this.referenceDistance = referenceDistance;
this.referenceIntensity = referenceIntensity;
}
public double distance2D(Point p1) {
return distance2D(p1, Point.ZERO);
}
public double distance2D(Point p1, Point p2) {
double distance = 0.0;
if ((p1 != null) && (p2 != null)) {
double dx = Math.abs(p1.x - p2.x);
double dy = Math.abs(p1.y - p2.y);
double ratio;
if (dx > dy) {
ratio = dy/dx;
distance = dx;
} else {
ratio = dx/dy;
distance = dy;
}
distance *= Math.sqrt(1.0 + ratio*ratio);
if (Double.isNaN(distance)) {
distance = 0.0;
}
}
return distance;
}
public double intensity(Point p) {
double intensity = 0.0;
if (p != null) {
double distance = distance2D(p);
if (distance != 0.0) {
double ratio = this.referenceDistance/distance;
intensity = this.referenceIntensity*ratio*ratio;
}
}
return intensity;
}
}
class Point {
public static final Point ZERO = new Point(0.0, 0.0, 0.0);
public final double x;
public final double y;
public final double z;
public Point(double x) {
this(x, 0.0, 0.0);
}
public Point(double x, double y) {
this(x, y, 0.0);
}
public Point(double x, double y, double z) {
this.x = x;
this.y = y;
this.z = z;
}
#Override
public String toString() {
return String.format("(%-10.4f,%-10.4f,%-10.4f)", x, y, z);
}
}
I'm new in open cl. And tried as my first work to write code that checks intersection between many polylines to single polygon.
I'm running the code in both cpu and gpu.. and get different results.
First I sent NULL as local parameter when called clEnqueueNDRangeKernel.
clEnqueueNDRangeKernel(command_queue, kIntersect, 1, NULL, &global, null, 2, &evtCalcBounds, &evtKernel);
After trying many things i saw that if i send 1 as local it is working good. and returning the same results for the cpu and gpu.
size_t local = 1;
clEnqueueNDRangeKernel(command_queue, kIntersect, 1, NULL, &global, &local, 2, &evtCalcBounds, &evtKernel);
Played abit more and found that the cpu returns false result when i run the kernel with local 8 or more (for some reason).
I'm not using any local memory, just globals and privates.
I didn't added the code because i think it is irrelevant to the problem (note that for single work group it is working good), and it is long. If it is needed, i will try to simplify it.
The code flow is going like this:
I have polylines coordinates stored in a big buffer. and the single polygon in another. In addition i'm providing another buffer with single int that holds the current results count. All buffers are __global arguments.
In the kernel i'm simply checking intersection between all the lines of the "polyline[get_global(0)]" with the lines of the polygon. If true,
i'm using atomic_inc for the results count. There is no read and write memory from the same buffer, no barriers or mem fences,... the atomic_inc is the only thread safe mechanism i'm using.
-- UPDATE --
Added my code:
I know that i can maybe have better use of open cl functions for calculating some vectors, but for now, i'm simply convert code from my old regular CPU single threaded program to CL. so this is not my concern now.
bool isPointInPolygon(float x, float y, __global float* polygon) {
bool blnInside = false;
uint length = convert_uint(polygon[4]);
int s = 5;
uint j = length - 1;
for (uint i = 0; i < length; j = i++) {
uint realIdx = s + i * 2;
uint realInvIdx = s + j * 2;
if (((polygon[realIdx + 1] > y) != (polygon[realInvIdx + 1] > y)) &&
(x < (polygon[realInvIdx] - polygon[realIdx]) * (y - polygon[realIdx + 1]) / (polygon[realInvIdx + 1] - polygon[realIdx + 1]) + polygon[realIdx]))
blnInside = !blnInside;
}
return blnInside;
}
bool isRectanglesIntersected(float p_dblMinX1, float p_dblMinY1,
float p_dblMaxX1, float p_dblMaxY1,
float p_dblMinX2, float p_dblMinY2,
float p_dblMaxX2, float p_dblMaxY2) {
bool blnResult = true;
if (p_dblMinX1 > p_dblMaxX2 ||
p_dblMaxX1 < p_dblMinX2 ||
p_dblMinY1 > p_dblMaxY2 ||
p_dblMaxY1 < p_dblMinY2) {
blnResult = false;
}
return blnResult;
}
bool isLinesIntersects(
double Ax, double Ay,
double Bx, double By,
double Cx, double Cy,
double Dx, double Dy) {
double distAB, theCos, theSin, newX, ABpos;
// Fail if either line is undefined.
if (Ax == Bx && Ay == By || Cx == Dx && Cy == Dy)
return false;
// (1) Translate the system so that point A is on the origin.
Bx -= Ax; By -= Ay;
Cx -= Ax; Cy -= Ay;
Dx -= Ax; Dy -= Ay;
// Discover the length of segment A-B.
distAB = sqrt(Bx*Bx + By*By);
// (2) Rotate the system so that point B is on the positive X axis.
theCos = Bx / distAB;
theSin = By / distAB;
newX = Cx*theCos + Cy*theSin;
Cy = Cy*theCos - Cx*theSin; Cx = newX;
newX = Dx*theCos + Dy*theSin;
Dy = Dy*theCos - Dx*theSin; Dx = newX;
// Fail if the lines are parallel.
return (Cy != Dy);
}
bool isPolygonInersectsPolyline(__global float* polygon, __global float* polylines, uint startIdx) {
uint polylineLength = convert_uint(polylines[startIdx]);
uint start = startIdx + 1;
float x1 = polylines[start];
float y1 = polylines[start + 1];
float x2;
float y2;
int polygonLength = convert_uint(polygon[4]);
int polygonLength2 = polygonLength * 2;
int startPolygonIdx = 5;
for (int currPolyineIdx = 0; currPolyineIdx < polylineLength - 1; currPolyineIdx++)
{
x2 = polylines[start + (currPolyineIdx*2) + 2];
y2 = polylines[start + (currPolyineIdx*2) + 3];
float polyX1 = polygon[0];
float polyY1 = polygon[1];
for (int currPolygonIdx = 0; currPolygonIdx < polygonLength; ++currPolygonIdx)
{
float polyX2 = polygon[startPolygonIdx + (currPolygonIdx * 2 + 2) % polygonLength2];
float polyY2 = polygon[startPolygonIdx + (currPolygonIdx * 2 + 3) % polygonLength2];
if (isLinesIntersects(x1, y1, x2, y2, polyX1, polyY1, polyX2, polyY2)) {
return true;
}
polyX1 = polyX2;
polyY1 = polyY2;
}
x1 = x2;
y1 = y2;
}
// No intersection found till now so we check containing
return isPointInPolygon(x1, y1, polygon);
}
__kernel void calcIntersections(__global float* polylines, // My flat points array - [pntCount, x,y,x,y,...., pntCount, x,y,... ]
__global float* pBounds, // The rectangle bounds of each polyline - set of 4 values [top, left, bottom, right....]
__global uint* pStarts, // The start index of each polyline in the polylines array
__global float* polygon, // The polygon i want to intersect with - first 4 items are the rectangle bounds [top, left, bottom, right, pntCount, x,y,x,y,x,y....]
__global float* output, // Result array for saving the intersections polylines indices
__global uint* resCount) // The result count
{
int i = get_global_id(0);
uint start = convert_uint(pStarts[i]);
if (isRectanglesIntersected(pBounds[i * 4], pBounds[i * 4 + 1], pBounds[i * 4 + 2], pBounds[i * 4 + 3],
polygon[0], polygon[1], polygon[2], polygon[3])) {
if (isPolygonInersectsPolyline(polygon, polylines, start)){
int oldVal = atomic_inc(resCount);
output[oldVal] = i;
}
}
}
Can anyone explain it to me ?
I needed to draw sphere on OpenGL without using gluSphere() function. I have found somewhere this function:
void drawSphere(double r, int lats, int longs) {
int i, j;
for(i = 0; i <= lats; i++) {
double lat0 = M_PI * (-0.5 + (double) (i - 1) / lats);
double z0 = sin(lat0);
double zr0 = cos(lat0);
double lat1 = M_PI * (-0.5 + (double) i / lats);
double z1 = sin(lat1);
double zr1 = cos(lat1);
glBegin(GL_QUAD_STRIP);
for(j = 0; j <= longs; j++) {
double lng = 2 * M_PI * (double) (j - 1) / longs;
double x = cos(lng);
double y = sin(lng);
glNormal3f(x * zr0, y * zr0, z0);
glVertex3f(x * zr0, y * zr0, z0);
glNormal3f(x * zr1, y * zr1, z1);
glVertex3f(x * zr1, y * zr1, z1);
}
glEnd();
}
}
But I can't understand what it does. I think it draws polyhedron that looks like sphere.
Also, I think lat0, lat1 used to determine how far from Z axis vertices will be located.
I am trying to implement a UI like this one..
http://www.shrenikvikam.com/wp-content/uploads/2011/04/214e422a43E11S3.png-150x134.png
But i am having some trouble implementing this.. Could someone tell me mistakes in this...
public class Meter extends View{
static final int ORBIT_COLOR = Color.argb(255, 66, 66, 66);
static final double RAD_CIRCLE = 2*Math.PI; // Number radians in a circle
private Paint paint; // Paint object controlling format of screen draws
private ShapeDrawable planet; // Planet symbol
private int planetRadius = 7; // Radius of spherical planet (pixels)
private int sunRadius = 12; // Radius of Sun (pixels)
private float X0 = 0; // X offset from center (pixels)
private float Y0 = 0; // Y offset from center (pixels)
private float X; // Current X position of planet (pixels)
private float Y; // Current Y position of planet (pixels)
private float centerX; // X for center of display (pixels)
private float centerY; // Y for center of display (pixels)
private float R0; // Radius of circular orbit (pixels)
private int nsteps = 120; // Number animation steps around circle
private double theta; // Angle around orbit (radians)
private double dTheta; // Angular increment each step (radians)
private double direction = -1; // Direction: counter-clockwise -1; clockwise +1
private float lastTouchX; // x coordinate of symbol i at last touch
private float lastTouchY; // x coordinate of symbol i at last touch
private int divisions = 120; // Since it requires temperature change from 0 -120
private double oneSegmentLength = (2 * Math.PI * R0)/(double)120;
public Meter(Context context) {
super(context);
// Initialize angle and angle step (in radians)
theta = 30;
//dTheta = RAD_CIRCLE/((double) nsteps); // Angle increment in radians
dTheta = ((360-60)/(double)divisions);
planet = new ShapeDrawable(new OvalShape());
planet.getPaint().setColor(Color.WHITE);
planet.setBounds(0, 0, 2*planetRadius, 2*planetRadius);
paint = new Paint();
paint.setAntiAlias(true);
paint.setTextSize(14);
paint.setStrokeWidth(1);
}
#Override
public boolean onTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
// MotionEvent class constant signifying a finger-down event
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
lastTouchX = x;
lastTouchY = y;
newXY();
break;
}
// MotionEvent class constant signifying a finger-drag event
case MotionEvent.ACTION_MOVE: {
float newX = ev.getX();
float newY = ev.getY();
float dx = newX - lastTouchX;
float dy = newY - lastTouchY;
int diff = (int) (Math.abs(ev.getX()) % Math.abs(oneSegmentLength));
if(diff == 0){
if(Math.abs(dx) > Math.abs(dy)) {
if(dx>0) direction = 1;
else direction = -1;
newXY();
} else {
newXY();
}
Log.d("MOVE", "dx ->" + dx + " one seg->" + oneSegmentLength);
invalidate();
}
break;
}
// MotionEvent class constant signifying a finger-up event
case MotionEvent.ACTION_UP: {
Log.d("ACTION MOVE","Value ->");
final float x = ev.getX();
final float y = ev.getY();
lastTouchX = x;
lastTouchY = y;
newXY();
break;
}
}
return true;
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
drawBackground(paint, canvas);
canvas.save();
canvas.translate(X + X0, Y + Y0);
planet.draw(canvas);
canvas.restore();
}
// Called by onDraw to draw the background
private void drawBackground(Paint paint, Canvas canvas){
paint.setColor(Color.YELLOW);
paint.setStyle(Paint.Style.FILL);
canvas.drawCircle(centerX + X0, centerY + Y0, sunRadius, paint);
paint.setStyle(Paint.Style.STROKE);
paint.setColor(ORBIT_COLOR);
canvas.drawCircle(centerX + X0, centerY + Y0, R0, paint);
}
//Method to increment angle theta and compute the new X and Y .
private void newXY(){
theta += dTheta;
Log.d("THETA VAL", "->" + theta);
//if(theta > RAD_CIRCLE) theta -= RAD_CIRCLE; // For convenience, keep angle 0-2pi
if(theta > 150)theta = 30;
if(theta > 30 && theta <120){
X = (float)(R0*Math.sin(direction*theta)) + centerX - planetRadius;
Y = centerY - (float)(R0*Math.cos(direction*theta)) - planetRadius;
}
//Log.i("ANIMATOR", "X="+X+" Y="+Y);
}
#Override
protected void onSizeChanged (int w, int h, int oldw, int oldh){
// Coordinates for center of screen
centerX = w/2;
centerY = h/2;
// Make orbital radius a fraction of minimum of width and height of display
R0 = (float) (0.90*Math.min(centerX, centerY));
oneSegmentLength = (2 * Math.PI * R0)/(double)120;
// Set the initial position of the planet (translate by planetRadius so center of planet
// is at this position)
X = centerX - planetRadius ;
Y = centerY - R0 - planetRadius;
}
}
I am referring this code to do this implementation...
http://eagle.phys.utk.edu/guidry/android/animatorDemo.html
I am just drawing a circle and trying to implement the same motion between 0 -120 degrees..