  We demonstrate practically approximation-free electrostatic calculations of
micromesh detectors that can be extended to any other type of micropattern
detectors. Using newly developed Boundary Element Method called Robin Hood
Method we can easily handle objects with huge number of boundary elements
(hundreds of thousands) without any compromise in numerical accuracy. In this
paper we show how such calculations can be applied to Micromegas detectors by
comparing electron transparencies and gains for four different types of meshes.
We demonstrate inclusion of dielectric material by calculating the electric
field around different types of dielectric spacers.
