# Tagged Questions

Scientific discipline dealing with the measurement and representation of the Earth's shape and gravitational field.

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### Which of EGM96 geoid or WGS84 ellipsoid fits the earth better?

ImageCredit Question If we separately add up |H| and |h| over the earth surface, which of the sums come out smaller? Background There is a phrase in the tag description of "ellipsoid" that says "...
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### Open Source Webmaps and Geotiffs

I have recently started to learn how to use open source web maps, and have come across the following issue. When using geoserver and geo explorer (part of the open-geo-suite), I seem to get an ...
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### Trilateration in 3D with signal strengths

I'm having a hard time getting my head around the maths to locate a target in 3D given a number of known points (4 or more) and a value that indicates the signal strength (range 0–100). I've looked ...
25k views

### Trilateration using 3 latitude and longitude points, and 3 distances

I want to find out an unknown target location (latitude and longitude co-ordinates). There are 3 known points (latitude and longitude co-ordinate pairs) and for each point a distance in kilometers to ...
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### PostGIS Geography Buffer producing different areas?

I'm trying to create circles of equal area in different places, but depending on the location of the centroid different areas are calculated. For example SELECT ST_Area(ST_Buffer('POINT(0 0)'::...
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### Using UTM Projection with Local Datums

Can somebody answer me is it okay to use UTM 42N Zone with Local Datum Everest 1830 (with applied transformation)in RTK Survey whereas UTM Projection is a default projection of WGS84 Datum.Will it ...
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### Geodesic replacement of coordinates [duplicate]

With a updatecursor I can move vertex to a new location and modify polygons. For a simpele example I tried to move the world, see image. The black lines are the 'edges' of world (180,90 -180,-90 ,-...
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### Strategies and methods that Datums and Coordinate Systems use to account for movement of the earth's surface

Are there datums and coordinate systems that address the issue of shifting coordinates through time? If so, what are some of the strategies and methods that the datums and coordinate systems use to ...
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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 ...
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### JTS Vividsolutions API: compute First (direct) geodetic problem

I'm using the popular JTS Vividsolutions API for Java. I'm struggling to find if I can perform calculation of the First (direct) geodetic problem with the API. Is there a way to calculate this with ...
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### Reverse Calculate Ellipsoidal Height

I have a few hundred points with ellipsoidal height taken a few years ago. Based on these ellipsoidal heights I had deduced orthometric heights for the same. Is there a way to find the ellipsoidal ...
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### How do you compute the earth's radius at a given geodetic latitude?

(I see there is an equation on wikipedia that does exactly what I am asking but there is no references. I have no way of confirming the validity of this equation!) I already understand the difference ...
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### What's wrong in using latitude and longitude as X and Y on a Cartesian space?

What can go wrong and what kind of error can build up if I use geodetic coordinates as if they were cartesian and place my objects into my world with no conversion formulas?
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### How do I account for changing latitude with a spatial filter?

I'm working with data in latitude/longitude grid form in a non-GIS specialised package (MATLAB) and wish to apply spatial filters to it. As this data contains a broad range of latitudes and is ...
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### What datum (reference ellipsoid) does Google Earth use?

What datum (reference ellipsoid) does Google Earth[1] use? I can't seem to find where Google Earth tells explicitly what datum they use. I need some sort of valid link. [1] The default free version ...
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### Which projection is suitable for the measurements of this great circle?

I have drawn a circle on google earth pro in such a way that its radius starts from earth center 0,0 (lat/long) and ends at 0,90 (lat/long). This circle divide the earth into two equall halfs as shown ...
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### Difference in destination location between pyproj and geopy

I am looking at ways to calculate (in Python) the destination location from a point given bearing and range. Based on the results comparison from the 2 libraries in subject(geopy and pyproj), I ...
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### Does GPS correct for continental drift?

Does GPS correct for continental drift, and if so, how? (I'm mainly interested from the perspective of consumer devices such as smartphones.)
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### Is WGS84 a Coordinate system or projection system? [duplicate]

WGS84 is often referred to as a "projection system" and sometimes it is confusing to me about what a "projection system" is and where WGS84 falls in one. Could someone please clear that up for me?
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### Set of intersection points in trilateration / multilateration [duplicate]

Like in this post I will get a set of points (3 or more) with latitude, longitude and distance (in KM) information to find out the target location. A distance could be about 500 KM. The circles (...
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### How to Convert Property Survey Monument Marker Coordinates to State Plane?

I have a set of Connecticut monument locations (a monumented property survey using monuments designated CGS Mon. No. 1577-1580). Their coordinates appear to me to be in meters (244536.84 N, 386409.67 ...
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### Learning classical geography - recommended literature etc

I've been working in the field of GIS for a few years now, and there are some disciplines of knowledge where I lack a good degree of education. My educational background is that I've studied computer ...
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### How can I use ArcGIS 10.1 to find a geodesic equidistant point defined by three points?

For example, I have coordinates for three base points on a coastline and I need to find the coordinates of the point off the coast which is equidistant from all three. It’s a simple exercise in ...
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### how to apply a canvas 'grid' to leaflet without curvature

I'm trying to create a grid of tiles in canvas to represent some data the original data comes with UK OSEAST1m and OSNORTH1m, i'm the grouping the data up into aggregates of, say 40km (as per the ...
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### Given distance (in meters) what is the angle in geographic reference systems? [duplicate]

In QGIS and other systems sometimes I have a layer in geographic reference system (typically WGS84, EPSG:4326) and I'd like to calculate a buffer of say 5000m around a point. So, given a point ...
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### Trilateration Calculation Issue

edit I was able to do this following partially from this solution: How to calculate the intersection of 2 Circles? I broke it up into 3 groups of intersections AB, AC and BC. Once I had those I took ...
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### Trilateration on a Sphere, given 2 points and 2 distances

Given the points: A) N 38° 38.000 W 90° 20.000 B) N 38° 39.000 W 90° 21.000 (I can calculate the distance between the 2 using a spherical earth model as 7710 feet, though it's not particularly ...
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### Calculate geographic position based on azimuth, distance and height [duplicate]

How to calculate the geographic position of an object in sky (Point B)(like an aircraft) from Home Point (Point A) based on only four variables: Lattitude and Longitude at Home Point, Azimuth at ...
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### <#> doesn't give a useful distance [duplicate]

I'm new to postgresql/postgis and trying to measure a distance. So st_distance() may be the most accurate, it's the slowest too (as I've read). I read that one can use geometric (instead of geographic)...
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### Scale on map requires correction coefficient. But why? [duplicate]

I am computing the distance of a map I am getting from ArcGIS' REST services by using a calculator as provided by this answer. In a nutshell, it uses a GeodeticCalculator for distance computation ...
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### Calculate end point Height above the MSL of the target point given a starting point, distance, azimuth and elevation [duplicate]

We need to find the end point height (from the earth surface) given the start point lat, lon, azimuth (270 deg), distance (500 km) and elevation above the horizon of start point (10 deg). The ...
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### Does the NED use geocentric or geodetic latitude?

What kind of latitude does the National Elevation Dataset (NED) use? Geocentric or geodetic or something else? I can't find the information anywhere on their site (http://ned.usgs.gov/index.html) or ...
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### Technique for splitting raster image into tiles

I have written a standalone application which renders a globe similar to GoogleEarth/WorldWind which is currently able to display raster imagery from WMS servers. The native geodesy of this ...
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### New coordinate system?

I just had my mind blown in answer to my previous question. I was going to rework that question, but decided it makes more sense to ask a new one. I had been converting between ECEF and lat/lon, and ...
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### Why not measure elevation from the center of the earth?

In trying to understand Geoid vs Ellipsoid height, I ran across this page. One of the claims is: Zero elevation as defined by Spain is not the same zero elevation defined by Canada Basically,...
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### Are ellipsoids a mathematical necessity?

The literature usually just tells us that the Geoid is complex to describe mathematically and that we therefore fit different Ellipsoids to approximate it. Are these Ellipsoids mathematically ...
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### Defining a line from geographic coordinate points.

On a flat surface we can define any point on line which passes from point1 (x1,y1) to point2 (x2,y2) via simple trigonometry. How can we do that with latitude and longitude of 2 points? Imagine we ...
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### Intersection between a ray from lat, lon, alt, with pan, tilt and earth's surface

I have a problem that consists of finding the intersection point between a ray from a given lat, lon, alt, that is looking to a given pan and tilt angles and the earth's surface. I need the lat, lon ...
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### 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 ...
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### What do different realizations of the same datum have in common?

Firstly, am I correct in assuming that the process of determining the shape and the size of the spheroid is independent from the process of determining the origin and the orientation? For example, ...
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### For a non-geocentric ellipsoid, how does the Lat/Long/Ell Ht & semi-major axis & flattening implicitly define the centre of the ellipsoid?

For example if we compare the AGD84 (Australian Geodetic Datum) with GDA94 (Geocentric Datum Australia), the centre of the AGD Datum is 200 metres different to GDA, because it is a best fit to the ...
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### Long range Trilateration from 3 lat, long, range

I've been looking at the following solution to a similar problem Trilateration using 3 latitude and longitude points, and 3 distances However with my problem the 3 points are spread over a large ...
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### Which training courses in Geodetics can you recommend?

Can anyone recommend any training courses in geodesy which would cover the following objectives: Case studies on coordinate issues Overview of geodetic datums, coordinate reference systems and ...
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### How to perform trilateration using 3 lat/lon points without distances? [closed]

I read this thread Trilateration using 3 latitude and longitude points, and 3 distances explaining about trilateration using 3 latitude and longitude with measured distance. The problem is I want to ...
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### How to generate geodesic linestring from two points in C#

I'm looking for a FREE C# class, library or set of functions that will allow me to generate a geodesic linestring (or array of vertices, whatever) from two decimal degree points. I've found ...
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### Which SRS is computational more effective to store continental scale data? (given some conditions)

For a Precision Agriculture application I need to make calculations in UTM projection. The data will be stored in Postgis and is made of soil samples results (point data) and field boundaries of many ...
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### What datum (reference ellipsoid) does Nasa Worldwind use?

What datum (reference ellipsoid) does Nasa Worldwind use? I can't seem to find where Nasa Worldwind tells explicitly what datum they use. I need some sort of valid link.
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### Attributes that characterize a geodetic track

I need a way to index and retrieve a large amount of track data. To do this I need to derive from every track as many attributes as I can. For now, I derive Name Tortuosity Speed (average, max) ...