diff --git a/docs/users_guide/framework_basics/the_affine_space.md b/docs/users_guide/framework_basics/the_affine_space.md index 085227d1c..af6e01a07 100644 --- a/docs/users_guide/framework_basics/the_affine_space.md +++ b/docs/users_guide/framework_basics/the_affine_space.md @@ -192,12 +192,22 @@ For this purpose, we can either use: static_assert(qp.relative() == 5406 * m); ``` +!!! note + + It is allowed to only covert between various origins defined in terms of the same + `absolute_point_origin`. Even if it is possible to express the same _point_ as a _vector_ + from another `absolute_point_origin`, the **mp-units** library will not allow it, and + a custom user-defined conversion function will be needed to provide such a functionality. + + Said otherwise, in the **mp-units** library, there is no way to spell how two distinct + `absolute_point_origin` types relate to each other. + + ### _Point_ arithmetics -Let's assume we are going to attend the CppCon conference that is hosted in Aurora, CO, and we -want to estimate the distance we are going to travel. We have to take a taxi to a local airport, fly to -DEN airport with a stopover in FRA, and in the end, get a taxi to the Gaylord Rockies Resort & Convention -Center: +Let's assume we will attend the CppCon conference hosted in Aurora, CO, and we want to estimate +the distance we will travel. We have to take a taxi to a local airport, fly to DEN airport with +a stopover in FRA, and in the end, get a cab to the Gaylord Rockies Resort & Convention Center: ```cpp constexpr struct home_location : absolute_point_origin {} home_location; @@ -258,8 +268,8 @@ using Celsius_point = quantity_point