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

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Calculate end point Height given a starting point, distance, azimuth and elevation

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) . Please ...
3
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1answer
124 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
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1answer
117 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 ...
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74 views

Learning classical geography - recommended literature et.c

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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1answer
83 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 ...
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0answers
74 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 ...
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0answers
146 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
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1answer
98 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
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1answer
96 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 ...
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1answer
252 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 ...
12
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3answers
515 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 ...
2
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1answer
317 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 ...
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0answers
73 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
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1answer
157 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 ...
21
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3answers
448 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 ...
3
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1answer
246 views

Trilateration on a Sphere given 2 points and 3 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. Given this segment and 2 other ...
2
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1answer
199 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 ...
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3answers
1k 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 ...
6
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3answers
509 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
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1answer
98 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
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1answer
331 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.
6
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2answers
3k 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 ...
11
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2answers
5k 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 ...
2
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1answer
145 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
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2answers
541 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 ...
2
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2answers
2k views

How to perform trilateration using 3 lat/lon points without distances?

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 ...
8
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1answer
122 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 ...
18
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5answers
9k 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 ...