Offset between canvas coordinates & aladin coordinates

[lsacienne]

Bug about the coordinates

There is a small offset created when going from Edition Mode (Javascript Canvas) to Browse Mode (On an aladin light layer). This offset is approximately of 1 pixel in x and y on the canvas.

Illustration

Edition Mode	Browse Mode

Cause

The problem probably comes from an approximation made to switch between a floating coordinate system ( in the sky coordinates system ) and the integer coordinate system used by the canvas. The conversion is not precise enough to ensure that the aladin lite background will fit with the canvas.

Potential solutions

• The first solution that comes to my mind is to use floor and ceiling functions inside the world2pixand pix2world methods. So we can maybe wrap those functions and use ceiling or floor to determine the better conversion.
• A second solution could be to increase the canvas resolution (if it possible) to have a better precision and a smaller offset