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

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21
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6answers
17k 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 ...
3
votes
2answers
119 views

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?
1
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0answers
11 views

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 ...
1
vote
2answers
49 views

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 ...
0
votes
1answer
36 views

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 ...
2
votes
1answer
112 views

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 ...
12
votes
3answers
808 views

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 ...
0
votes
0answers
37 views

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 ...
0
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0answers
50 views

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 ...
3
votes
1answer
160 views

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.)
0
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0answers
158 views

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 ...
3
votes
1answer
361 views

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 ...
2
votes
1answer
66 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 ...
1
vote
0answers
31 views

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 ...
3
votes
1answer
74 views

<#> 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 ...
2
votes
0answers
36 views

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 ...
0
votes
0answers
35 views

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 ...
4
votes
3answers
580 views

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 ...
2
votes
1answer
527 views

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 ...
3
votes
1answer
151 views

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 ...
3
votes
1answer
173 views

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 ...
22
votes
3answers
540 views

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 ...
1
vote
1answer
124 views

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 ...
1
vote
0answers
213 views

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 ...
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 ...
2
votes
0answers
488 views

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 ...
2
votes
1answer
113 views

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, ...
3
votes
1answer
136 views

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 ...
13
votes
2answers
8k views

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 ...
1
vote
1answer
428 views

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 ...
1
vote
0answers
106 views

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 ...
7
votes
2answers
6k views

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 ...
7
votes
1answer
194 views

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 ...
2
votes
2answers
3k views

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 ...
2
votes
1answer
245 views

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 ...
6
votes
3answers
676 views

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 ...
1
vote
1answer
109 views

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 ...
1
vote
1answer
419 views

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.
2
votes
1answer
155 views

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) ...
12
votes
2answers
777 views

How do you find a lat/lon (DMS) on a paper map using a 30cm ruler?

How do you use a 30cm ruler to find DMS on a paper map? The locations I would like to find are the 'corner' points so I can generate an extent based on the four corners. I have an old paper map (3 ...
8
votes
1answer
129 views

Is there a geodetic benchmark that is fixed with respect to plate tectonics?

I see that NGS benchmarks are used to monitor the movement of geologic plates. Is one of the benchmarks assumed to be in a fixed location, with movements of all other benchmarks measured with respect ...