LibreCAD
Circle tangent to 3 Cirles fails
While trying to create a fourth (red) circle tangent to other 3 circles, LibreCAD fails to draw the circle in this particular arrangement.
It will not let you select the third circle no matter what order you choose them .
Intended behavior: have LibreCAD draw the red circle upon choosing the other 3 circles.
@hhassey
Could you upload a sample dxf with this issue? I cannot reproduce this issue with the latest (2.2.2_alpha)
@dxli Github would no let me upload dxf file. but here it is a link to it I am using: Version: v2.2.1.1 Compiler: GNU GCC 14.2.1 Compiled on: Feb 19 2025 Qt Version: 5.15.17 Boost Version: 1.87.0 System: Arch Linux
The root cause: failure of the Algebraic algorithm as described here https://en.wikipedia.org/wiki/Problem_of_Apollonius, when the x-coordinates or y-coordinates of input circle centers are identical.
The fix in 3c4196e: when the algebraic algorithm fails, falls back to a generic center finding algorithm by the paths of shared tangential circles of two given circles.