How do you control the force arrow base location?

There is no direct method to chose between those 2 options. However, the point of action of the arrow can be precisely defined using the “ForceReport” object which takes 3 inputs “Type”, “r” and “n”. It is important to remember that the position of the point of Action is arbitrary, and that by default, Gomboc takes the point which is the shortest distance on the line of action of the force to the origin. All coordinates are given in the common reference frame defined at the root of the boc file by “ForceReportFrameName”. Three options are available to the user:

• Specify “r” and set type to “NearestToPoint”. The point of action is positioned on the line of action to be at the shortest distance from the point “r”:

"ForceReport" : {
"Type" : "NearestToPoint",
"r" : [0, 0, -2.00],
}

• Specify “r” and “n” and set type to “NearestToLine”. The point of action is positioned on the line of action to be at the shortest distance from the line defined by the direction “n” and the point “r”:

"ForceReport" : {
"Type" : "NearestToLine",
"r" : [0, 0, 0],
"n" : [0, 1, 0],
}

• Specify “r” and “n” and set type to “PlaneIntersection”. The point of action is positioned on the line of action to be at the shortest distance from the plane defined by the normal “n” and the point“r”:

"ForceReport" : {
"Type" : "PlaneIntersection",
"r" : [0, 0, 0],
"n" : [0, 1, 0],
}