This is mike’s answer with some annotations for the magic numbers. It seemed to work fine for me for some test data: function calc_distance($point1, $point2) { $radius = 3958; // Earth’s radius (miles) $deg_per_rad = 57.29578; // Number of degrees/radian (for conversion) $distance = ($radius * pi() * sqrt( ($point1[‘lat’] – $point2[‘lat’]) * ($point1[‘lat’] – … Read more
A distance matrix is a lower triangular matrix in packed format, where the lower triangular is stored as a 1D vector by column. You can check this via str(distMatrix) # Class ‘dist’ atomic [1:10] 1 4 10 15 3 9 14 6 11 5 # … Even if we call dist(vec1, diag = TRUE, upper … Read more
These sort of questions come up all the time (for me–and as evidenced by the r-tagged SO question list–others as well): is there a function, either in R core or in any R Package, that does x? and if so, where can i find it among the +2000 R Packages in CRAN? short answer: give … Read more
I accept the question has been answered adequately (with the obvious caveats of requiring level ground and possible accuracy problems) but for those who don’t believe it can be done or that it needs a video camera, let me explain the low-level math needed to do it…. The picture above shows me standing outside my … Read more
You get position by integrating the linear acceleration twice but the error is horrible. It is useless in practice. Here is an explanation why (Google Tech Talk) at 23:20. I highly recommend this video. However the gyro mouse might work for your application, see between 37:00-38:25 in the video. Similar questions: track small movements of … Read more
Calculate a bounding box to select a subset of the rows in the WHERE clause of your SQL query, so that you’re only executing the expensive distance calculation on that subset of rows rather than against the entire 200k records in your table. The method is described in this article on Movable Type (with PHP … Read more
Loading the geosphere package you can use a number of different functions library(geosphere) distm(c(lon1, lat1), c(lon2, lat2), fun = distHaversine) Also: distHaversine() distMeeus() distRhumb() distVincentyEllipsoid() distVincentySphere() …
Ok, for starters, you don’t really need to use the Haversine formula here. For large distances where a less accurate formula produces a larger error, your users don’t care if the match is plus or minus a few miles, and for closer distances, the error is very small. There are easier (to calculate) formulas listed … Read more
What you’re using is called the haversine formula, which calculates the distance between two points on a sphere as the crow flies. The Google Maps link you provided shows the distance as 2.2 km because it’s not a straight line. Wolfram Alpha is a great resource for doing geographic calculations, and also shows a distance … Read more
Perhaps you should check out (PDF warning! Also note that, for some reason, the order of the pages is reversed) “Optimal Algorithms for Computing the Minimum Distance Between Two Finite Planar Sets” by Toussaint and Bhattacharya: It is shown in this paper that the minimum distance between two finite planar sets if [sic] n points … Read more