Linked Questions

20
votes
3answers
23k views

Algorithm to find nearest point

I've a list of a few hundred cities with their latitude/longitude. Given another location (also in lat/long) I need to find the nearest city. As I don't use any GIS, by now the obvious algorithm is ...
19
votes
3answers
24k views

What is unit of shapely length attribute?

I'm doing a very simple calculation of the length of a polyline using shapely: from shapely.geometry import LineString ... xy_list = [map(float,e) for e in xy_intm] line = LineString(xy_list) s = '%...
11
votes
3answers
4k views

What is the right solution (and map projection) to compute distances between points located all over the World?

After my study on map projection I realized that it is very difficult to choose a projection that allows to compute simultaneously the distances between a great deal of points if these points are ...
8
votes
3answers
6k views

Which is the most accurate method of measuring distance?

I aim to analyse the accuracy of the various methods of geodesic calculations (distance between two points on Earth)based on the three assumed models of Earth - flat, spherical & ellipsoidal. I ...
2
votes
3answers
2k views

Why is this polygon "self intersected" and invalid?

I have a polygon defined as follows: segment from 43:29:02 N 003:50:39 E to 43:34:12 N 003:43:04 E arc(CW): center (43:34:49 N 003:58:16 E) from 43:34:12 N 003:43:04 E to 43:45:45 N 003:59:56 E ...
7
votes
2answers
4k views

Find tangent point on circle furthest east or west

There are few ways of articulating my question. It starts with a known circle on a sphere, i.e. a point-radius, and one that does not cover a pole. I would like to calculate the point furthest west ...
5
votes
2answers
989 views

What is a delta in lat/lon called?

What is the delta between two lat/lon pairs called? Delta degrees? Arcs? Is it some quantity of distance but what is its unit of measurement? And related: Can we use pythagoras to calculate this ...
1
vote
2answers
10k views

Generate random location within specified distance of a given point

In a simulation (not using any GIS), I need to generate a random location that is within a specified distance of a given location. I found a very helpful post here on this exact topic: How to ...
0
votes
2answers
536 views

Getting a "square" of lat/lon for database query [duplicate]

So I want to get the square formed by a single point of lat/lons, my plan was to take that point's latitude, divide by 360, and multiply by the circumference of earth. Giving us the distance from the ...
5
votes
1answer
2k views

What kind of margin of error can I expect in figuring distance?

I have reviewed Why is law of cosines more preferable than haversine when calculating distance between two latitude-longitude points? and that does not equate to the specific question that I wish to ...
4
votes
1answer
1k views

JTS - Java Topology Suite - Calculate radius from a given point

From point A, I want to check if a point B is within a certain radius from A. How calculate it usindo JTS? I tried this: Coordinate posicaoAtual = new Coordinate(-12.974900375893823, -38....
2
votes
1answer
3k views

Creating Longitude and Latitude Lines in Google Maps

I'm working on an independent high school project where i'm trying to build a simple differential equation model for diffusion. I'm trying to overlay the model on top of a map to visualize spread, so ...
2
votes
1answer
110 views

Center-to-Center distance [duplicate]

Possible Duplicate: What is the right solution (and map projection) to compute distances between points located all over the World? I want to know how I could calculate the center-to-center ...
1
vote
1answer
2k views

Distance between two latitudes [duplicate]

I need to know the distance in feet between the coordinates N34-00.000 and N34-00.001 (Degrees, minutes and thousanths of minutes) I computed approx 6 feet but am not confidant in my math skills.
0
votes
1answer
592 views

What Spatial Reference System do I store Google Map's Lat/Lng in [duplicate]

I am new to PostGIS, Spatial Reference Systems and projections and want to store lat/lng coordinates retrieved from Google Maps and its services like the Geocoder. I'm working with data in America and ...

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