\( I(x,y)=\int_0^D \) \(C\)\((\)\(s\)\((\)\(\mathbf{x}(\lambda)\)\()))\)\(\tau\)\((\)\(s\)\((\)\(\mathbf{x}(\lambda)\)\())) \times \exp\left(-\int_0^\lambda\tau(s(\mathbf{x}(\lambda'))) \mathrm{d}\lambda'\right)\mathrm{d}\lambda\),