When I work with polygon, there is a function geometry.getInteriorPoint(). What does interior point mean. What point in polygon is this one?
It is a point that falls within the polygon for sure and in most cases that point matches the centroid of the polygon. Generally, it is used for label placement
My feature was a multypolygon so I had to do something like this in order to get the internal coordinates:
const multipolygon: MultiPolygon = this.selectedGeometry.getGeometry() as MultiPolygon
const polygon: Polygon = multipolygon.getPolygon(0)
const pos: Coordinate = initial(polygon.getInteriorPoint().getCoordinates())
The initial() is from loadash and it drops the last coordinate.
Related
Because of the Moodle-STACK environment I am currently limited to JSXGraph 0.99.7. Is there a way to get the union of two curves given by coordinate vectors (polygons) in that version?
In 1.2.1 I do this using Clip.union(), which works fine in jsfiddle (not exactly a minimum working example) but not in STACK.
this.b = board.create('curve', JXG.Math.Clip.union( bneu, this.b, board),
{opacity: true, fillcolor:'lightgray', strokeWidth: normalStyle.strokeWidth,
strokeColor: normalStyle.strokeColor});
In 0.99.7 you have to do the union by hand. As long as the shapes are not overlapping this might be doable without too much work. Define a curve and set its
updataDataArray method:
c = board.create('curve', [[], []]);
c.updateDataArray = function() {
this.dataX = [];
this.dataY = [];
// copy now the coordinates of the polygons / curves into
// these arrays.
};
board.update();
You can access the coordinates of the polygon vertices by
polygon.vertices[i].X();
polygon.vertices[i].Y();
Attention: the last vertex is a copy of the first vertex, to make the polygon a closed curve.
The coordinates of a curve can be accessed by
curve.points[i].usrCoords[1]; // x-coordinate
curve.points[i].usrCoords[2]; // y-coordinate
The curve path can be interrupted by adding NaNs:
this.dataX.push(NaN);
this.dataY.push(NaN);
Hope that helps a little bit.
I'm using ArUco markers to correct perspective and calculate sizes in an image. In this image I know the exact distance between the outer edges of the markers and am using that to calculate the sizes of the black rectangles.
My problem is that aruco::detectMarkers doesn't always identify the true edges of the markers (as shown in the detail image). When I correct the perspective based on the corners of the markers, it causes distortion that affects the size calculations of the objects in the image.
Is there a way to improve the edge detection accuracy of aruco::detectMarkers?
Here's a scaled-down photo of the entire board:
Here's the detail of the lower-left marker showing the inaccuracy of the edge detection:
Here's the detail of the upper-right marker showing an accurate edge detection of the same marker ID:
It's hard to see in this shrunken image but the upper-left marker is accurate and the lower-right marker is inaccurate.
My function that calls detectMarkers:
bool findMarkers(const Mat image, Point2d outerMarkerCoordinates[], Point2d innerMarkerCoordinates[], Size2d *boardSize) {
Ptr<aruco::Dictionary> theDictionary = aruco::getPredefinedDictionary(aruco::DICT_4X4_1000);
vector<vector<Point2f> > markers;
vector<int> ids;
aruco::detectMarkers(image, theDictionary, markers, ids);
aruco::drawDetectedMarkers(image, markers, ids);
return true; //There's actually more code here that makes sure there are four markers.
}
Examination of the optional detectorParameters argument to detectMarkers showed a parameter called doCornerRefinement. Its description is "do subpixel refinement or not". Since the error I'm seeing is larger than a pixel, I didn't think this was applicable to my situation. I gave it a try anyway and experimented with the cornerRefinementWinSize value and found that it did indeed solve my problem. Now I'm thinking that "pixel" in the ArUco sense is the size of one of the squares within the marker, not an image pixel.
The modified call to detectMarkers:
bool findMarkers(const Mat image, Point2d outerMarkerCoordinates[], Point2d innerMarkerCoordinates[], Size2d *boardSize) {
Ptr<aruco::Dictionary> theDictionary = aruco::getPredefinedDictionary(aruco::DICT_4X4_1000);
vector<vector<Point2f> > markers;
vector<int> ids;
Ptr<aruco::DetectorParameters> detectorParameters = new aruco::DetectorParameters;
detectorParameters->doCornerRefinement = true;
detectorParameters->cornerRefinementWinSize = 11;
aruco::detectMarkers(image, theDictionary, markers, ids, detectorParameters);
aruco::drawDetectedMarkers(image, markers, ids);
return true; //There's actually more code here that makes sure there are four markers.
}
Success!
I am trying to calculate the coordinates along a circle corresponding to the tap location. The coordinates should be on the border of the circle nearest to the tap location (e.g. the border that is less distant from the radius). To facilitate this I am detecting only taps that are distant by 80% of the radius from the circle center.
Input:
P (GPPoint) - center of the circle
P1 (GPPoint) current position of an image displayed
r (float) radius of circle
P3 (CGPoint) user tap coordinate
Desired output:
P2 (CGPoint) - new coordinates for the image corresponding to P3 but along the circle. Sorry for the bad explanation, I try to explain it in other words: once the user taps on the screen I would like to move the image in P2. P2 should be derived by moving P2 to the border of the circle. It should be possible to do so by using the radius information.
The idea is to create from P3 coordinates a new coordinate called P2 as described above - the key is that P2 distance from the centre should correspond exactly to the radius and the ANGLE should be the same as tapPoint.
Would anyome be able to suggest a formula to calculate the corresponding coordinate given a tap? I simply need to calculate P3 using the input I have.
Code so far:
-(void)tapInImageView:(UITapGestureRecognizer *)tap
{
CGPoint tapPoint = [tap locationInView:tap.view];
if ([self isInOuternCircle:tapPoint]) {
// then create from tapPoint coordinates a new coordinate P2 as described above - but have no idea how.. the key is that P2 distance from the centre should correspond exactly to the radius and the ANGLE should be the same as tapPoint.
}
}
-(BOOL)isInOuternCircle:(CGPoint)point
{
double distanceToCenter = sqrt((point.x - _timerView.center.x)*(point.x - _timerView.center.x) + (point.y - _timerView.center.y)*(point.y - _timerView.center.y));
if (distanceToCenter < _innerCircleRadius) {
return false;
}
return true;
}
I've done this once before, but the math usually depends on how you've set up your coordinate system, so I'll just outline what I did. You'll need a bit of geometry, and a few formulae to determine the new coordinate along the circle.
Calculate the formula of a line passing through the center (P) and your tap point (P3) using this: http://en.wikipedia.org/wiki/Linear_equation#Two-point_form
Determine the equation for your circle: http://en.wikipedia.org/wiki/Circle#Equations
Using the above two equations, you'll have a system of a linear and a quadratic equation: http://www.mathsisfun.com/algebra/systems-linear-quadratic-equations.html
Once you have the equation above, you need to solve it. The result will yield two possible points (the line will intersect the circle in two places), and the point you are looking for is the point closer the tap point. In this case, just compare the distances to P3 between the two solutions, and the shorter distance will show your required solution - P2.
1) I am using MKMapView to display a custom Image (for example width=350 cm,height =230 cm) in a MKOverlayView.
2) The center of the Image is now at longitude=0 and latitude = 0 and covers the whole world
4) I place a MKPointAnnotation at longitude = 60.749995 and latitude =56.091651
Now I want convert this Point(Longitude,Latitude) back to x,y in cm.
So that I can create a JPG on the server with the annotation on top of the Image.
So how do I calculate the x,y values?
Thanx Craig
so something like:
CLLocationCoordinate2D coordinateOrigin = CLLocationCoordinate2DMake(90, -180);
CLLocationCoordinate2D coordinateMax = CLLocationCoordinate2DMake(-90, 180);
MKMapPoint maxMap=MKMapPointForCoordinate(coordinateMax);
MKMapPoint minMap=MKMapPointForCoordinate(coordinateOrigin);
double width = maxMap.x-minMap.x;
double height = maxMap.y-minMap.y;
MKMapPoint p = MKMapPointForCoordinate(wanted_coord);//wanted_coord is the one needed
double pixel_x=p.x/width;
double pixel_y=p.y/height;
1) You're not really dealing with cm, you're dealing with pixels. An image has a certain number of pixels in each direction, the physical measurement of cm depends on how big your screen/printer's pixels are.
2) to convert from lat long to pixels use MKMapPoints via the MKMapPointForCoordinate function. That will give you a x/y coordinate and you'll need to scale those values to fit your custom image, therefore you need to work out what MKMapPoints it covers. For example if your image covered the entire world you could find the minimum values for MKMapPoint by using MKCoordinateForMapPoint with (-180,-90) and the maximum values with (180,90). Now you'll have the max/min for MKMapPoint's x and y, you know the max/min for your image, so it's trivial to scale from one to the other.
Basically i have a list of POI's (name,lat,long) and i want to draw them on the UIView, relative to my current lat/long. I'm looking for some best practice for mapping these POI (lat/long) to a UIView.
I don't want to use MKMapView (no need for displaying map-data).
I was reading:
http://developer.apple.com/library/ios/#documentation/general/conceptual/Devpedia-CocoaApp/CoordinateSystem.html
But I'm clueless how i get from a CLLocation to a (x,y) on my UIView. I only want to draw those POI's around my current location. So, for example if my screen would represent a 20 by 30 KM region, how do i map my POI's to their corresponding (x,y) coordinates?
Thanks.
What you're doing is a little strange, but you can convert latitude/longitude to a CGPoint-like struct called an MKMapPoint. An MKMapPoint has an x and y value which correspond to points on a map. Imagine if you laid out a flat map of the world, and 0,0 was the top left. MKMapPoint is a point on that map using that coordinate system.
Use the function MKMapPointForCoordinate() to convert a CLLocationCoordinate2D to an MKMapPoint
MKMapPoint myMapPoint = MKMapPointForCoordinate(myLocationCoordinate);
When you get the list of points, you'll have to do something like finding the max and min x and y values, then fitting all the points into your view using those values, otherwise you'll end up with a load of very close points in one place in your view.
My guess is that, for a 20KM by 30KM region, you can consider the earth to be flat and there fore linearly extrapolate the coordinates. I am sure you can google and find out as to how much distance is a difference in 0.00001 in latitude and longitude.
So if you have 20Km to be represented on X axis, and your current location is 30.1234567 in latitude, and 0.0000001 is 1 km then you can put your coordinate in the center of the screen and 30.1234557 as the left most X coordinate and so on.
I am not trying to provide an answer here, but just trying to think out loud, because I wanted to do some thing similar as well and did it as an Internet based app (without display though), where given two coordinates, I had to find the distance between them.
There are many (many) different approaches to modelling the planet and translating 3D coordinates onto a 2D surface, and the errors introduced by the various methods vary depending on what part of the globe you are. This question seems to cover most of what you are after though:
Converting Longitude & Latitude to X Y on a map with Calibration points
I think its best way (correctly work for Mercator projection map):
extension UIView
{
func addLocation(coordinate: CLLocationCoordinate2D)
{
// max MKMapPoint values
let maxY = Double(267995781)
let maxX = Double(268435456)
let mapPoint = MKMapPointForCoordinate(coordinate)
let normalizatePointX = CGFloat(mapPoint.x / maxX)
let normalizatePointY = CGFloat(mapPoint.y / maxY)
let pointView = UIView(frame: CGRectMake(0, 0, 5, 5))
pointView.center = CGPointMake(normalizatePointX * frame.width, normalizatePointY * frame.height)
pointView.backgroundColor = UIColor.blueColor()
addSubview(pointView)
}
}
My simple project for adding coordinate on UIView: https://github.com/Glechik/MapCoordinateDrawer