# Tagged Questions

Any line bisecting the surface of a sphere into two equal halves.

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### What shows the Tissot's indicatrix on a mercator projection?

While reading this post on Quora: https://www.quora.com/Why-does-Google-use-the-Mercator-projection-on-their-maps-as-opposed-to-an-equal-area-proportion-map, I understand that with a mercator ...
62 views

### How a draw a circle (on the surface of earth) on a mercator projection?

I would like to use R and leaflet to draw a circle (a real circle on the surface of the earth) on a mercator projection. In the following code, I have the center of the circle (with lng=0 and lat=60),...
352 views

### How to make Great Circle Arcs which look good on a Web Mercator map?

I'm trying to create a map, with data indicating some flights, and want to use Great Circle Arcs, to connect the source and destinations. Basically, I want to do something similar to the famous ...
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### Great circles path not curved (in R)? Conventions and convertions problems?

I am given the great circle equations of two paths. The first one is Longitude = 168 degree. and the second one is: tan(Lattitude)=.11 cos(Longitude) + .64 sin(Longitude) However, I am ...
105 views

### Which projection can I use to see alignments on great circles?

I want to put on a QGIS map some historical sites to check if they are aligned. If an alignement exists, the points should stay on a great circle (is this correct?). I want to visually verify this ...
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### Is there any online viewer which displays the polygons assuming great circle lines for the edges?

My question is similar to this one: Are there any online WKT editors? The links given in answers have been very useful to me. However, it seems that when the tools in question display maps, they ...
372 views

### Project location on a (great circle) path

I've been searching this SE site for quite a few hours now, and I'm still struggling to find a solution to my question. My goal is that given a way in OSM and my location (lat/lon coordinates), I want ...
324 views

### Modifying straight line segments so they follow geodesic / great circle paths using QGIS

I have a kml file showing a dodecahedron stretched across the surfce of a globe, which I downloaded here: http://montalk.net/cgi-bin/coordinates.py I would like to re-project this dodecahedron so I ...
664 views

### great circles in QGIS and export in 3857 webmap

My plan is to visualize great circles in a leaflet webmap. So coming from this great postgis article and R version I thought it would work like this in QGIS: create line from two points, store ...
327 views

### Find latitude of point on great circle given longitude

I am trying to find out wether my implementation has faults and/or if there is a better method. The problem: Given two points (Lat/Long) defined over the WGS84 ellipsoid, find the point lying on ...
285 views

### Moving dead ahead: rhumb line, great circle or none

I think I understand the whole rhumb line and great circle idea but I can't seem to find an answer on this question. Suppose I am driving a car (i don't use ship because I don't want to put the ...
395 views

### How to prevent cross-world lines in ggplot world map?

I'm having issues displaying 'great circles' paths and polygons in ggmap, an extension of ggplot2. Please enter the following code to replicate my issues: https://gist.github.com/Robinlovelace/...
861 views

### cross track distance to great cicle line and rhumb line

How to calculate cross track distance to great cicle line and rhumb line? For great circle line, I've tried this formula, but it is not accurate while the distance is less than 0.1nm. For rhumb ...
300 views

### Google Earth / QGIS projection (great circle line)

Here is my question: 1- Based on a long distance segment ( approx 2000 km) drawn on Google Earth and imported as shapefile in QGIS I want to obtain a terrain profile based on "Terrain Profile" plugin....
265 views

### Should geometries be drawn using rhumb-line or great-circle paths?

I work with WGS-84 coordinates and, most of the time, my map display (luciadmap) is in Mercator projection. My client is surprised to see that, for a rectangular geometry: the line between the 2 ...
118 views

### Drawing smooth great circle?

I want to draw smooth great circle in any scale and any distance on a Mercator map. The key problem here is how many intermedia points do I need for different location and distance to draw it smoothly ...
191 views

### Does PostGIS have a Vincenty Distance calculation?

I have compared some distance calculations between geopy and PostGIS ST_Distance_Sphere, and it seems that PostGIS ST_Distance uses a calculation that is similar to the great circle distance rather ...
177 views

### Air corridor in spherical surface: calculating great circle tangent points with small circles

I have the necessity to draw on a sphere (earth) an air corridor. In the cartesian plane, this corridor is made by some circles and from outer tangents that connect these circles as you can see in ...
475 views

### Draw great circle rays from a single point along specific directions

How can I draw great circle rays starting from a single given point P (for example, from coordinate [34 N, 116 W] in this map) and along directions D1, D2, ... (for example, 30, 45 and 135 degrees) in ...
251 views

### Can I cross the dateline in CartoDB?

I've created a lovely route map in CartoDB, but one of the lines crosses the dateline (from Colorado to Guam, FWIW) and finds its way there by hitting the dateline north of Alaska, bouncing back ...
5k views

### What's the difference between vincenty and great circle distance calculations?

Python's geopy package features two distance measurements techniques: Great Circle and Vincenty's formulae. >>> from geopy.distance import great_circle >>> from geopy.distance ...
476 views

### Where to start with great circle maps in CartoDB?

I've pulled together a series of maps in R based on Nathan Yau's excellent Great Circles tutorial and a nice zipcode package The maps show how many people from many zip codes descended on a single zip ...
489 views

### How to determine vector between two lat/lon points

For all the math geniuses out there...given two lat/lon points (point A and point B), what is the simplest way to find the vector needed to reach point B from point A. For example, the vector needed ...
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### Draw cirlcle on Equirectangular projection [duplicate]

I'm trying to draw a circle (actually a great circle) on an equirectangular map to archive something like this http://i.stack.imgur.com/7EliU.png (from here). So I have the lat/lon coordinates of the ...
308 views

### How to calculate smallcircle on sphere

I use this python code to calculate a greatcircle: https://code.google.com/p/pyroms/source/browse/trunk/pyroms/greatcircle.py?r=39 After initializing the greatcircle I can calculate points on the line....
794 views

### Lines as Great circles on a map

How can I get line features to appear as great circles on a map, instead of straight lines? Thanks,
1k views

### Great-circle lines in Equirectangular projection

Just to check that I'm on the right track: Are all great-circles on the sphere and in equirectangular projection (i.e. latitude, longitude pairs) either: meridians (i.e. going pole to pole) of the ...
405 views

### Point plus distance along great circle using RGeo or WKT

I'm racking my brains (and google) trying to figure out how to get RGeo to do the following geospatial calculation: Imagine I start off at some arbitrary geographic point (let's say (45, 45) which ...
668 views

### Find points of interest near a path?

Imagine a table of points of interest along with lat/long. The user identifies two of these points. I want to do the following: Calculate a great-circle path between these points Find all POIs that ...
519 views

### Are long lines in shapefiles to be considered geodesics or straight lines in the 2D latlong space?

Is there a definition on how lines connect vertices in the shapefile format? In the simplest case, imagine a line with only 2 points, from 40,-118 to 40,-112 - that's somewhere random in the US - ...
2k views

### WGS point to WGS line segment (great circle) distance

How would I go about resolving this in C#? I have a line segment (great circle distance) defined by two Lon-Lat pairs (call them points A and B). A third point somewhere on the Earth sphere. The ...
1k views

### Is there a way to get ST_ClosestPoint for Geography type?

Using PostGIS 2.0.0 I'd like to find the point on a LINESTRING that is closest to a given point. The LINESTRING represents a great circle line (ie. geography type). ST_ClosestPoint appears to do ...
1k views

### How do I find the points of intersection between a small circle and a great circle?

I only actually need to intersect a great circle arc i.e. the shortest path between two points, with a given small circle. I found this tutorial for intersecting two great circle arcs, but ...
4k views

### Distance between lat/long points

I am attempting to calculate the distance between two latitude/longitude points. I have a piece of code that mostly works that I yanked from this post but I do not really understand how it works. ...