FAQ

Geodesy

GCTool

Geodesy

What's earth?

Well, if you're not extraterrestrial, it is the thing you're living on. Meanwhile it's a grain of salt in space... Some interesting measures about earth:

Mean radius:6,371 km
Equatorial radius:6.378.1 km
Polar radius:6,356.8 km
Surface area:510,072,000 km2 (29.2% land, 70.8% water)
Volume:1.0832073 x 1012 km3
Mass:5.9736 x 1024 kg

Mathematically, earth can be approximated by an ellipsoid. The parameters forming such an ellipsoid are called a 'reference datum'. A worldwide used 'datum' is WGS84, which was introduced by the US Army. More information about datums can be read on wikipedia.

GCTool

What does the CCP tool do?

The CCP tool calculates the bearing and distance between two points. Suppose that the green area in the image is a piece of earths surface. Two points are specified by 'A' and 'B'. The CCP tool determines the distance and bearing from point 'A' to point 'B'.
If the distance is small, the line between the points is straight. But for larger distances, we have to take in account that the earth has an ellipsoidal shape. This can be seen in the image. Luckily you don't have to worry about this, because GCTool takes the shape in account by default. One funny remark can be made... If you're walking a long distance in a straight line over this ellipsoid, your final bearing (when you arrived at 'B') will be in general different then your initial bearing (just after departure at 'A'). The CCP tool shows only the initial bearing.

What does the PCC tool do?

The PCC tool does it just the other way around (compared to CCP). Suppose you're standing on point 'A' and the distance and bearing to 'B' are given... Then the PCC tool calculates the position of point 'B'.
Like in the CCP case, GCTool takes by default in account that earth is not flat, not a sphere, but something like an ellipsoid. This means again that the initial bearing could be different then the final bearing (see 'What does the CCP tool do?'). GCTool assumes that your input bearing is the initial bearing.

What does the LLC tool do?

The LLC tool calculates the crossing points of two lines, each specified by two coordinates. Suppose that the green area in the figure is a piece of earths surface, then points 'A' and 'B' define a line and points 'C' and 'D' define a line. The LLC tool calculates position '?'.
Nowadays we live after Pythagoras, which has made our world more difficult. Roughly before Pythagoras, people thought that the earth was a flat plane. Pythagoras posed that the earth had to be a sphere, and later it became clear that the earth is an ellipsoid. Why all this history? Now, this means that if we continue walking along the two lines, there must be another crossing point at the other side of earth. That's why the LLC tool shows two results.

Is it possible to run GCTool on linux?

Yes, it is. NogeenGuus provided me the following nice tutorial. To start of with, some preparations:

  • Download Wine via your favorite package manager.
    Wine is a tool to run windows applications on your linux machine.
  • Download WineTricks.
    WineTricks is a handy script for downloading and installing extra Windows parts.
  • Download GCTool.

Okay, now the preparations are done, we're ready for the real work. Open a terminal and use the commands below to install GCTool. Lines that start with a dash (#) are comments and should be discarded. Lines starting with a dollar sign ($) are the actual commands. While executing a command, you should not type the "$" itself, only what's behind.

# Allow WineTricks to be executed:
$ chmod u+x winetricks.sh

# Install dotnet 2.0:
$ ./winetricks.sh dotnet20

# When the installation of dotnet is finished it's time for GCTool.
# Unpack it:
$ unzip GCTool-1-6-1.zip

# Then start the installation:
$ wine setup.exe

# and see if it works!
$ wine start "c:\program files\GCTool\GCTool.exe"

Of course it's not very smart to use the commandline each time you run GCTool. Maybe it's better to create a shortcut. How that works is up to you!

 

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