In my iPhone app, suppose I have the coordinates of the current location. I want to know the coordinates of a point 10km from here, and 30° North East for example. How do I calculate it? Thanks.
After typing a bunch of formulae out, I realized there's a site that already has it down, so I'm just going to link that instead, Calculate distance and bearing between two Latitude/Longitude points. The section titled "Destination point given distance and bearing from start point" is what you want. Just convert the degrees to radians (your bearing) and you'll be all set
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I have the ephemeris for an Earth observing satellite from a TLE, so I can get the location of the satellite (lat/lon). The documentation has a nice example for the ISS, showing how that is done.
However, what I am actually after is the location of the point of the Earth's surface that the satellite's sensor is pointing at. Assume that the sensor is pointing perpendicular to the flight direction, so I should be able to calculate the azimuth direction using the satellite's inclination. Then I have an idea of the angle the satellite's sensor is using to point to the ground. Some simple geometry should give me the altitude I need.
The question is now: How do I string these two things together? The compute(observer) calculation example returns altitude and azimuth for a location (lat/lon). However, I could not find anything that does that the other way around. Any thoughts how to go about this? Any clues are much appreciated.
I need a set of equidistant points (like a raster) each in a 1km distance to the next over a certain area, in my case Germany. I know the feature "regular points" in QGis where I can do just that but the distance you can enter there is not in meters but in coordinates or something. I tried it in WGS 84 as well as in EPSG:31467 (Gauss-Kruger, common in Germany) which is supposed to be in meters but the results seem to be the same..
I just can't find a way to set a certain distance in meters.
Please help :) Thanks!
I am looking for how to calculate the distance along a path in a binary array.
I imported a map as a matrix in matlab. There is a binary image of a river crossing two cities. I only found out how to calculate the distance from the river points to the nearest city but I don't manage to compute the shortest distance along the river.
I made a vector with the indices of all river points but I don't know how to get the distance to the nearest city from that...
Image
So I am looking for the shortest distance through the red line towards one of the light blue points it crosses !
Thnx
If I understand you in the right way it is not very difficult: Just do a dfs or bfs (8-neighbourhood) starting at each river-town and add sqrt(2) if you go diagonal and 1 if you go to a 4-neighbour. At each river pixel you can finally decide by taking the minimum value. You can develop it further stopping at river pixels with already smaller distance to another city...
I really hope I got you in the right way :)
I have data describing a rotated ellipse (the center of the ellipse in latitude longitude coordinates, the lengths of the major and minor axes in kilometers, and the angle that the ellipse is oriented). I do not know the location of the foci, but assume there is a way to figure them out somehow. I would like to determine if a specific latitude longitude point is within this ellipse. I have found a good way to determine if a point is within an ellipse on a Cartesian grid, but don't know how to deal with latitude longitude points.
Any help would be appreciated.
-Cody O.
The standard way of doing this on a Cartesian plane would be with a ray-casting algorithm. Since you're on a sphere, you will need to use great circle distances to accurately represent the ellipse.
EDIT: The standard ray-casting algorithm will work on your ellipse, but its accuracy depends on a) how small your ellipse is, and b) how close to the equator it is. Keep in mind, you'd have to be aware of special cases like the date line, where it goes from 179 -> 180/-180 -> -179.
Since you already have a way to solve the problem on a cartesian grid, I would just convert your points to UTM coordinates. The points and lengths will all be in meters then and the check should be easy. Lots of matlab code is available to do this conversion from LL to UTM. Like this.
You don't mention how long the axes of the ellipse are in the description. If they are very long (say hundreds of km), this approach may not work for you and you will have to resort to thinking about great circles and so on. You will have to make sure to specify the UTM zone to which you are converting. You want all your points to end up in the same UTM zone or you won't be able to relate the points.
After some more research into my problem and posting in another forum I was able to figure out a solution. My ellipse is relatively small so I assumed it was a true (flat) ellipse. I was able to locate the lat lon of the foci of the ellipse then if the sum of the distances from the point of interest to each focus is less than 2a (the major axis radius), then it is within the ellipse. Thanks for the suggestions though.
-Cody
I am struck with a problem. I want to convert the CMAttitude information of an iPhone to Altitude (0 to 90deg) and Azimuth (0 to 360 deg). I have googled around and hit some threads which discuss about it, but none of threads turn out with a positive answer and most of the articles discussing Quaternion and Euler angles are too much mathematics to stuff into my brain!
Is there some open source material which does this task easy? Or someone has written code to perform this conversion?
Edit:
First off, sorry for being so abstract!
Azimuth is the direction on the surface of the earth towards which the device is pointing. Like North = 0 deg, North East = 45deg, East = 90 deg, South = 180 deg and so on. Ranges between 0 deg to 360 deg:
Altitude is the angle made from the plane of the earth to an object in the sky:
Thanks,
Raj
Using CMDeviceMotion, you can get a CMAttitude object with "roll, pitch and yaw" - where for example, given a phone held in portrait mode "yaw" is "azimuth", "pitch" is the tilt of the phone with respect to ground, or zenith, and "roll" is about the vector pointing through the screen and not what you're interested in.
Things get a bit tricky because "azimuth" is a projection of the 3D magnetic vector (pointing towards the magnetic north pole) on to the flat "ground" plane, which changes depending on device orientation, but given this understanding of the terms, threads like this one should be much more understandable. If you only need your application to work in one orientation things get much simpler.
P.S. "altitude" is almost exclusively used to refer to elevation or height about a given reference (sea level, geodetic height etc). "Zenith" or "pitch" are preferable, and since you're on iOS, you should stick to their coordinate scheme: (lat, lon, alt), (pitch, yaw, roll).