Tagged Questions

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

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4
votes
1answer
52 views

What information is needed to determine the section of the earth's surface visible in a photograph?

What information (either provided by a user or taken from sensor readings) would be required to determine the geographic area encompassed by a photograph? It seems like the area visible from a ...
0
votes
1answer
45 views

Rhumb lines intersection

I looking for algorithm how to find out whether two rhumb lines given by point1 with azimuth1 and point2 with azimuth2 have intersecting point. Have anyone idea how to find intersection ? For ...
15
votes
3answers
5k views

Why is law of cosines more preferable than haversine when calculating distance between two latitude-longitude points?

In fact, when Sinnott published the haversine formula, computational precision was limited. Nowadays, JavaScript (and most modern computers & languages) use IEEE 754 64-bit ...
12
votes
2answers
188 views

What is the approximate error of the Pythagorean Theorem vs. Haversine Formula in measuring distances on a sphere at various scales?

Many people when first trying to calculate distances between two longitude / latitude pairs ask if Pythagorean theorem works as an appropriate distance function. Most often people answer "no, the ...
1
vote
1answer
27 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 ...
3
votes
1answer
113 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
votes
0answers
102 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) * ...
12
votes
2answers
258 views

Bilateration - 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 ...
1
vote
1answer
144 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 ...
8
votes
1answer
158 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
212 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 ...
21
votes
3answers
11k views

Algorithm for offsetting a latitude/longitude by some amount of meters

I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...
2
votes
0answers
55 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 ...
5
votes
1answer
321 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 ...
7
votes
2answers
479 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
votes
0answers
86 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 ...
6
votes
2answers
150 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, ...
6
votes
1answer
124 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 ...
4
votes
2answers
528 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 ...
14
votes
1answer
493 views

How accurate is approximating the Earth as 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 ...
5
votes
2answers
150 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
67 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
273 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 :)
5
votes
2answers
409 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 ...
11
votes
2answers
779 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 ...
3
votes
1answer
115 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 ...
9
votes
1answer
253 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: ...
5
votes
2answers
2k 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
2answers
288 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 ...
0
votes
0answers
258 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 ...
8
votes
1answer
377 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
399 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
123 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
234 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
140 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 ...
0
votes
2answers
3k 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?
2
votes
2answers
536 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
554 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 ...
34
votes
5answers
3k 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 ...
5
votes
1answer
597 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 ...
6
votes
3answers
1k 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
136 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 ...
2
votes
2answers
661 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 ...
3
votes
2answers
412 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
164 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?
10
votes
2answers
1k 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 ...
9
votes
3answers
629 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
172 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 ...
5
votes
2answers
220 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 ...
2
votes
5answers
2k 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 ...

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