Spherical geometry is the geometry of the two-dimensional surface of a sphere.

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868 views

How to calculate midpoint given north/south latitude and east/west longitude?

First, sorry if this questions sound very simple. I am very new to GIS. Given four values of north/south latitude, east/west longitude how to calculate the center point that is correct for all cases ...
3
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0answers
778 views

Bearing/Course/Heading in WGS84 ellipsoid model

There is a common formula for computing the initial bearing for a course from lat1, lon1 to lat2, lon2. (And yes, I'm aware that the course will change when traveling). atan2( sin(lon2-lon1) * ...
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vote
1answer
912 views

Lat Long line intersecting with circle

Can anyone help me what's the algorythm to calculate points of intersection whet is given one point p1 [lat,long] , bearing x (let say 137 degrees), arc center [lat,long] and radius? I woulde like to ...
10
votes
1answer
660 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 ...
0
votes
1answer
585 views

Convert Lat/Lon to Pixel-XY on cropped map

I've got a little problem. I have a GPX-Track containing LatLon coordinates based on WGS84. The track should be drawn on a cropped map, and for this, I need the pixel coordinates. The map tiles are ...
2
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0answers
104 views

Find arc endpoint with bearing and radius counting with curvature of the earth?

So my problem is that I have start point [lat,long] for arch, bearing, radius and I need compute end point [lat,long] ? End point should be in 180 degrees angle from start point and I should be aware ...
18
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3answers
2k views

How to calculate the intersection of 2 Circles?

I'm trying to figure out how to mathematically derive the common points of two intersecting circles on earth's surface given a center Lat/Lon and a radius for each point. Ex. Given: Lat/Lon ...
8
votes
2answers
1k views

Nearest point on a line ( Spherical / Mercator projection )

I have a line (Ax,Ay - Bx,By) over a mercator projection (google maps) and a random point (Cx,Cy) nearest to that line, i would to know the closest point (transparent blue on the image) over that line ...
2
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0answers
176 views

Centroid of the equator and a point

Suppose I already have a way to compute the centroids of different geometry types: Points (arithmetic mean of Cartesian coordinates). Linestrings (polylines) (weighted mean of segment mid-points in ...
7
votes
2answers
2k views

Calculating a spherical polygon centroid

I'd like a general way to calculate centroids for polygons on a sphere. So far, the best online reference appears to be: Tools for Graphics and Shapes by Jeff Jenness. The method described ...
6
votes
1answer
200 views

How do I represent the whole Earth as a Polygon?

This is related to determining the interior of a Polygon. My difficulty is that if I specify a Polygon covering the Earth going from East to West, it will still have a boundary along the ...
7
votes
2answers
291 views

How do different GIS systems determine a Polygon's interior?

I'm interested in understanding how real-world GIS systems and their data encode Polygons. Specifically, how do they resolve the ambiguity of a Polygon's interior on a sphere? Background: in 2D, ...
5
votes
2answers
185 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 ...
2
votes
0answers
128 views

Placement of a fixed-radius circle on a sphere to maximize point containment

There are many papers on the "Circle Placement Problem" in 2D Euclidean space, but I haven't been able to find any papers discussing this problem on the sphere. The problem is: given a set of points ...
4
votes
1answer
856 views

Line intersection with circle on a sphere (globe or earth)

How can I find the intersection point of a line and a circle on a sphere (on earth) Please, if any one knows a good solution help. Thanks in response :)
6
votes
1answer
1k views

Find Perpendicular Distance and Minimum Perpendicular Vector between a Point and a Line using GeoTools and JTS

I have a line formed by 2 lat/lon pairs, and the lat/lon of a point. I would like to find out the perpendicular distance between the line and the point on the Earth surface (can assume Earth as great ...
5
votes
2answers
778 views

Identify the latitudinal and longitudinal point directly beneath an object in space

Given the azimuth and altitude / latitude and longitude from the observer to the satellite, how can I accurately find the latitude and longitude of the point of intersection directly under the ...
15
votes
2answers
2k views

Calculate distortion outside a UTM zone

One of my colleagues is working with data that is spread across two UTM zone. The majority of the data is in one zone, with a few outliers in another zone. He would like to know what the area ...
10
votes
1answer
605 views

How to visualize azimuthal data with uncertainties?

I am trying to make a figure showing azimuthal data with a different range of uncertainties at each point. This oldschool figure from a 1991 paper captures the "bowtie plot" idea that I'm aiming for: ...
2
votes
3answers
2k views

Local Coordinate to Geocentric

The ultimate question, I need a transformation matrix to take a point in local space representing a roughly 500m x 500m place in New Mexico centered at -108.619987456 long 36.234600064 lat. The final ...
0
votes
0answers
474 views

Implementing custom (Vincenty/Haversine formula) functions for MySQL vs Using PostGIS?

I currently am using MySQL for all of my relational data. I have hit a crossroads with geo calculations. Since, MySQL does not have good support for spatial functions, I am contemplating on using ...
4
votes
2answers
1k views

How to calculate area of 1 x 1 degree cells in a raster

I have a simple array (not geo-referenced in any way) in Matlab (which is not a language I know a huge amount about...so I can export it to other languages if needed) which has the dimensions 180 x ...
8
votes
1answer
874 views

Given a line on the earth's surface, how do I plot a line perpendicular to it?

Given a line on the earth's surface, how do I plot a line perpendicular to it? Apologies if this is a very simple question. I thought this would be a straightforward task, but it is proving ...
2
votes
1answer
781 views

MySQL GeoSpatial function for ST_Distance_Spheroid? Metric used in return Type of GLength?

Is there a ST_Distance_Sphere, ST_Distance_Spheroid equivalent function in MySQL's GeoSpatial Support? If not, any way to emulate this? What is the metric used in return type of ...
0
votes
1answer
209 views

Spherical Mercator to Cylinder mercator?

Hello I want to create an overlay for google maps. As far as I know google maps using Spherical Mercator, so the system where I read the maps use Mercator but is not specified which (spherical or ...
6
votes
2answers
428 views

how to find the point in a country furthest from a boundary

i'm trying to find the point in south africa furthest from the sea or a landward boundary. my method thus far: i obtained a first guess at the centre of the inscribed circle and the three segments ...
3
votes
1answer
144 views

Is there a straightforward way to tweak LatLon on a sphere to represent true LatLon?

I have no experience in mapping, so please excuse me if this sounds foolish. I'm trying to use Microsoft MapPoint (2004) software to geocode a number of addresses in Excel. However, my version of ...
3
votes
1answer
237 views

Dividing a geographic region

I have a certain geographic region defined by the bottom left and top right coordinates. How can I divide this region into areas of 20x20km. I mean in practial the shape of the earth is not flat it's ...
27
votes
2answers
2k views

How accurate is approximating the Earth as a sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
3
votes
2answers
961 views

Finding the minimum and maximum distance between an observer and a lat/lon bounding box

I have three points in geographic coordinates (latitude, longitude, altitude). One of the points represents an observer, above the Earth. The other two points define a bounding box. I'd like a ...
1
vote
2answers
828 views

OpenLayers Circle not visible

I'm trying to draw a circle with OpenLayers with a Google Maps Layer. I'm able to transform a simple marker and have it draw at the correct location, but I can't figure out the circle. I'm trying to ...
6
votes
1answer
1k 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 ...
7
votes
3answers
2k views

How to find a point half way between two other points?

I'm working on implementing the OSM Mobile Binary format for map data, and because it uses a 16 bit delta for each point along a way, it cannot represent a way if there is a large distance between two ...
5
votes
2answers
169 views

Distortion of equally sized world tiles

My question is related to this: http://stackoverflow.com/questions/7927863/location-data-format-for-adehabitat-package I have a relational database with 'world tiles'. Each tile has a side length of ...
3
votes
2answers
1k views

ST_Distance versus ST_Distance_Spheroid?

As my client software uses lat/lon coordinates when communicating with my (spherical mercator) postgis database i decided to ST_Transform every geometry to WGS-84. However i noticed that ST_Distance ...
0
votes
2answers
6k views

How to convert lat long to meters using Mercator projection in C#

I have set of lat long values and I want their equivalent in meters using Mercator projection in C#. Can you please post some sample code or api example of some library that does exactly this?
3
votes
2answers
706 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 ...
5
votes
1answer
252 views

Intermediate points on a small circle

I need to interpolate lat/lon points along a small circle, with a given centre and radius. I've successfully used these formulas for great circles. What is the equivalent for small circles?
9
votes
3answers
1k views

How can I find the most remote spot in Eastern United States?

I have this hunch that I could travel no more than 50 miles from the most remote spot in the Eastern United States (east of the Mississippi River), in the direction of the nearest road, and find a ...
1
vote
1answer
229 views

Lambert cylindrical projection support in PostGis

Does PostGis support Lambert cylindrical projection or is there a way to add support for it? I'm probably searching the wrong terms, but google isn't bringing up anything useful. Any help is ...
6
votes
3answers
5k views

How to convert Distance, Azimuth, Dip to XYZ?

I have an excel spreadsheet with header and survey drill data. Header data contains hole ID, and location coordinates, and the survey data contains related downhole survey with Distance, Azimuth and ...
4
votes
5answers
6k views

Calculate midpoint from a series of latitude and longitude coordinates

I've got a series of longitude and latitude coordinates which represent a building outline e.g. -0.5485381346101759,53.2285150736142 -0.5482220594232723,53.22842450827133 ...
13
votes
3answers
3k views

Lon/lat transformation

First I should clarify I don't have previous experience with the field, so I don't know the technical terminology. My question is as follows: I have two weather datasets: The first one has the ...
5
votes
1answer
1k views

How do I find the intersections of 2 circles on earths surface?

I have the circles' center in lat & long, as well as the radius in meters. How do I find the circles intersections? Edit: EXAMPLE: Circle 1: Center on Earth's surface (43.564627,-116.220524) ...
2
votes
1answer
794 views

XY to Line tool crashing

The problem I'm encountering is simple. I have a shape file of points (about 8 million). They have three XY pairs that I am attempting to create XY lines from for purposes of measuring distance. ...
7
votes
1answer
711 views

How does one calculate an angle in a geographic coordinate system?

Given three points on a line in a geographic coordinate system, how does one calculate the angle formed by these three points? Please, give a general solution but also include system specific ...
5
votes
2answers
2k views

Converting Longitude and Latitude Coordinates to Square Miles?

I have a set of Long and Lat co-ordinates making up a five point polygon which I have converted in excel using the following formula: ...
10
votes
4answers
934 views

How to calculate the visible sky percentage

Hi I am writing a project and I am stuck: can anyone explain as simply as possible how to calculate the visible sky percentage? I have done a satellite survey and have worked out the height of ...
5
votes
2answers
296 views

Does the Chamberlin trimetric projection map (some) great circles to straight lines?

I know that, in general, the Chamberlin trimetric projection maps most great circles on the sphere to some sort of non-straight curve on the flat map. But what about the 3 special great circles ...
37
votes
5answers
8k views

Why is the 'straight line' path across continent so curved?

This is the result of mapping the straight line path from a point in US to Poland using Distance Measurement Tool. Also, planes from Asia to US would travel almost over North Pole. Why is the path ...