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!
Related
I am using the DBSCAN algorithm to determine clusters in a data set obtained by an automotive radar. The paper "Grid-Based DBSCAN for Clustering Extended Objects in Radar Data" from Dominik Kellner, Jens Klappstein and Klaus Dietmayer (link below) proposes a Grid-Based DBSCAN method. Therefore, the search radius epsilon variates in azimuth direction depending on the range. The radius in range direction stays constant. The normal DBSCAN is using Euclidean distance metric to determine the epsilon-neighbourhood where the search radius is the same in both directions. I cannot find out how to have an ellipse-search instead of a circular.
Do you know a distance metric that is working elliptical? Or, can you provide me with a short code that solves my problem? I am using MATLAB but the code can be in your prefered language.
Let's give an example so we talk about the same:
Consider a cartesian coordinate system with range in meters plotted against azimuth angle in degrees. The search distance in the range direction should be three meters (or possible observation points) in both directions from a centre point. In azimuth direction, the search radius should be five points in both directions.
If you cannot think of an elliptical solution, maybe a linear works as well.
Thank you for your help.
https://www.researchgate.net/profile/Dominik_Kellner2/publication/261127945_Grid-based_DBSCAN_for_clustering_extended_objects_in_radar_data/links/57742a7708aead7ba06e60b5.pdf
I have a question about if something is possible using Tableau.
I already have a coastline plotted on one map using custom LatLon coordinates and I would like to take a user inputted Lat and Lon and plot a circle around it with let's say radius 10 and display it on the same map.
I was using this tutorial before to plot a circle:
https://www.crowdanalytix.com/communityBlog/customers-within-n-miles-radius-analysis-using-tableau
But I don't think the same approach can work with user-inputted fields because then it would require restructuring the data..
Okay, a (much smarter LOL) coworker helped me figure this out....
So my goal was to graph distance band (like a distance of 5 miles around a coast) . In order to do this we can use the distance between two coastline points since they are connected by a line, not a curve...From there we can find the perpendicular point a certain distance away and connect those points. Much easier than my circle idea...
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
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