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2d
answered More accurate way to calculate area of rasters
2d
comment More accurate way to calculate area of rasters
If your system supplies an atanh function, then you can slightly more accurate results (less round-off) replacing log(zp/zm) by 2*atanh(e*sin(f)).
Nov
24
answered cross track distance to great cicle line and rhumb line
Nov
9
revised cross track distance to great cicle line and rhumb line
Add link to geo.javawa.nl
Nov
9
answered cross track distance to great cicle line and rhumb line
Nov
6
revised Prior art on rhumb line and great ellipse areas?
Planimeter now supports rhumb lines
Nov
4
answered Prior art on rhumb line and great ellipse areas?
Nov
4
comment How can I measure area from geographic coordinates?
Thanks! I've fixed it.
Nov
4
revised How can I measure area from geographic coordinates?
added 77 characters in body
Nov
3
comment Best formula for calculating short distances in UTM?
GeoConvert (written by me) will compute the UTM scale for you. In the first example, the scale at the mid-point is given by "echo 17n 645084 4833438 | GeoConvert -c -p 3". The second number 0.9998589143 is the scale. 30000/0.9998589143 = 30004.233 m which is within 3cm or 0.0001% of the true answer.
Nov
3
awarded  Student
Nov
3
comment Prior art on rhumb line and great ellipse areas?
Danielsen dx.doi.org/10.1179/003962689791474267 solved the problem where the edge is a geodesic in 1989 and that solution is employed by GeographicLib. Extending the technique to rhumb lines and great ellipses is straightforward enough (see the links in the question).
Nov
2
comment Prior art on rhumb line and great ellipse areas?
Consider measuring the area of an polygon where one side is a rhumb line running SE from 39N 120W to 35N 115.0107164W (part of the border between California and Nevada). This "line" becomes a curve in the Lambert equal-area cylindrical projection (and most other equal area projections). So you'll need to insert intermediate points on rhumb line to be able to represent the polygon accurately in an equal-area projection. So instead of doing one unit of work to calculate the area contribution of this edge, you'll have to do 630 units of work (assuming you need to insert one point per km).
Nov
2
comment Prior art on rhumb line and great ellipse areas?
@mdsumner, you're right that using an equal angle projection is the standard way to handle area calculations. However, the need to insert (a possibly large number of) intermediate vertices makes this method equivalent to "slicing the area into many strips". As a result, the calculation either slow or inaccurate or both. I'm interested in methods which don't have this limitation.
Nov
2
awarded  Revival
Nov
1
answered How to calculate the area of an ellipse on the earth's surface using Python?
Nov
1
asked Prior art on rhumb line and great ellipse areas?
Oct
16
comment Geometric Operations in GIS Systems
This link geo.javawa.nl/coordcalc/index_en.html solves various problems (line intersections, etc.) using geodesics. The calculations are all done in Javascript and I believe that it calls my Javascript implementation of the geodesic routines in GeographicLib
Sep
24
comment How to calculate the shortest geographical distance between a line and a point?
My solution is given in sourceforge.net/p/geographiclib/discussion/1026621/thread/… this uses C++. However the solution can be implemented in Java too, since the needed functions are in the Java version of GeographicLib
Aug
19
revised What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation?
Add information on the closest approach problem