Wikipedia gives a pretty thorough discussion of the algebra here: http://en.wikipedia.org/wiki/Trilateration The first step, not really covered in the Wikipedia entry, is to convert your lat/long coordinates to Cartesian coordinates: x0 = cos( lon0 ) * cos( lat0 ) , y0 = sin( lon0 ) * cos( lat0 ) , z0 = sin( lat0 ) … Read more
I ended up using the suggestion from JoshO’Brien mentioned above and found here. I took his code and changed state to county as shown here: library(sp) library(maps) library(maptools) # The single argument to this function, pointsDF, is a data.frame in which: # – column 1 contains the longitude in degrees (negative in the US) # … Read more
For latitudes use: Decimal(8,6), and longitudes use: Decimal(9,6) If you’re not used to precision and scale parameters, here’s a format string visual: Latitude and Longitude ##.###### and ###.###### To 6 decimal places should get you to around ~10cm of accuracy on a coordinate.
I checked on internet for various polygon area formulas(or code) but did not find any one good or easy to implement. Now I have written the code snippet to calculate area of a polygon drawn on earth surface. The polygon can have n vertices with each vertex has having its own latitude longitude. Few Important … Read more
Since you are creating two layers (one for the polygons and the second for the labels), you need to specify the data source and mapping correctly for each layer: ggplot(ny, aes(long, lat)) + geom_polygon(aes(group=group), colour=”black”, fill=NA) + geom_text(data=cnames, aes(long, lat, label = subregion), size=2) Note: Since long and lat occur in both data frames, you … Read more
The term you’re looking for is geocoding and yes Google does provide this service. New V3 API: http://code.google.com/apis/maps/documentation/geocoding/ Old V2 API: http://code.google.com/apis/maps/documentation/services.html#Geocoding
The service has been stopped. It is the 8th of March. See the top of this page for information on the death of v2 See The Google Geocoding API for v3 … Edit. Actually, there is a page about upgrading to v3 that may be of use. … Edit. As just pointed out, the Geocoding … Read more
This is called Reverse Geocoding Documentation from Google: http://code.google.com/apis/maps/documentation/geocoding/#ReverseGeocoding. Sample Call to Google’s geocode Web Service: http://maps.googleapis.com/maps/api/geocode/json?latlng=40.714224,-73.961452&sensor=true&key=YOUR_KEY
No, there is not really any other way : if you have many locations and want to display them on a map, the best solution is to : fetch the latitude+longitude, using the geocoder, when a location is created store those in your database, alongside the address and use those stored latitude+longitude when you want … Read more
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