Method, performed by one or more devices (405; 430; 434; 900), for provision of a pair of real world and image sensor correspondence points for use in calibration of an imaging system for three dimensional imaging based on light triangulation, said imaging system comprising a camera (430; 530) with image sensor and a light source (410; 510) for providing a light plane (411; 511), said light triangulation involving imaging by said camera of reflected light resulting from said light plane (411; 511) intersecting with and thereby causing reflections from a surface, said correspondence points being a real world point (514-1; 529-1), located in said light plane (411; 511), and an image sensor point (544-1; 554-1) that corresponds to where said real world point (514-1; 529-1) is imaged on the image sensor by the imaging system, wherein the method comprises: - providing said real world point (514-1; 529-1) as a first virtual intersection between a first real world line (512a; 527a) and a second real world line (512b; 527b), wherein said first real world line (512a; 527a) corresponds to a first real intersection between a first real surface (521a; 526a) and the light plane and wherein reflected light from said first real intersection is captured by the image sensor of the imaging system in a first image (540a; 550a), and wherein said second real world line (512b; 527b) corresponds to a second real intersection between a second real surface (521b; 527b) and the light plane (411; 511) and wherein reflected light from said second real intersection is captured by the image sensor of the imaging system in another, second, image (540b; 550b); and - providing said image sensor point (544-1; 554-1) as a second virtual intersection between a first image line (542a; 552a) corresponding to positions of intensity peaks of said captured light in the first image (540a; 550a) and a second image line (542b; 552b) corresponding to positions of intensity peaks of said captured light in the second image (540b; 550b). - providing said real world point (514-1; 529-1) as a first virtual intersection between a first real world line (512a; 527a) and a second real world line (512b; 527b), wherein said first real world line (512a; 527a) corresponds to a first real intersection between a first real surface (521a; 526a) and the light plane and wherein reflected light from said first real intersection is captured by the image sensor of the imaging system in a first image (540a; 550a), and wherein said second real world line (512b; 527b) corresponds to a second real intersection between a second real surface (521b; 527b) and the light plane (411; 511) and wherein reflected light from said second real intersection is captured by the image sensor of the imaging system in another, second, image (540b; 550b); and wherein said first real world line (512a; 527a) corresponds to a first real intersection between a first real surface (521a; 526a) and the light plane and wherein reflected light from said first real intersection is captured by the image sensor of the imaging system in a first image (540a; 550a), and wherein said second real world line (512b; 527b) corresponds to a second real intersection between a second real surface (521b; 527b) and the light plane (411; 511) and wherein reflected light from said second real intersection is captured by the image sensor of the imaging system in another, second, image (540b; 550b); and - providing said image sensor point (544-1; 554-1) as a second virtual intersection between a first image line (542a; 552a) corresponding to positions of intensity peaks of said captured light in the first image (540a; 550a) and a second image line (542b; 552b) corresponding to positions of intensity peaks of said captured light in the second image (540b; 550b).