SciDraw: Adding Canvas coordinates to plot coordinates

Question

The following code

<< SciDraw`;
Figure[
 FigurePanel[
  {FigLine[Plot[x, {x, 0, 1}]];
   p1 = {30, 80};
   p2 = DisplacePoint[p1, Canvas[{20, 20}]];
   FigInset[Show[Graphics[Circle[{0, 0}, 1]]], Transpose@{p1, p2}];
   }],
 CanvasSize -> {4, 3}
 ]

fails with

Transpose::nmtx: The first two levels of {{30,80},Object[Object$1058]}
cannot be transposed.

Why is that? The documentation claims that

The DisplacePoint function generates a new point by moving a given vector displacement “relative to” a given point. (You can actually add several displacements d1 , d2 , . . .at once.) A displacement may be given as {dx,dy}, Scaled[{dx,dy}], or Canvas[{dx,dy}]

What is the type returned by this DisplacementPoint? How can I convert it back to regular coordinates?

Answer 1

Indeed, as Szabolcs points out in the comments, AnchorCoordinates is used to convert any SciDraw points to coordinates, not just anchors. This is how it works:

Figure[
  FigurePanel[{
    FigLine[Plot[x, {x, 0, 1}]];
    p1 = {0.8, 0.6};
    p2 = DisplacePoint[p1, Canvas[{20, 20}]];
    FigInset[Show[Graphics[Circle[{0, 0}, 1]]], 
      Transpose@{p1, AnchorCoordinates[p2]}];
   }],
 CanvasSize -> {4, 3}]

and with 40 instead of 20 pixels in Canvas[...]

One application for this approach is to create regions that are square on the canvas but located at given plot coordinates.