**What is a 2D Grid?** A **2D grid** is a regular spatial discretization of an area into equally sized **cells**.\\ Each cell represents a spatial unit for which values (e.g. elevation, thickness, parameters) are defined. A crucial aspect of a grid definition is **how the position of each cell is referenced**. ---- **Grid Cells vs. Grid Points** A common source of confusion is the distinction between: * **Grid cells** (areas) * **Grid points** (coordinates) In GeoScene3D, grid-based data are internally defined using **grid points**, not full polygons. ---- **Grid Origin in GeoScene3D** GeoScene3D defines the **grid origin (null point)** at the **lower-left corner of the grid**. This means: * The grid coordinates start in the lower-left corner * Cell spacing is applied in positive x- and y-directions from this point This definition is consistent with many numerical and interpolation-based grid formats. ---- **Cell Reference Point: Center of the Cell** Although the grid origin is located at the lower-left corner, **GeoScene3D defines grid values at the center of each cell**. In practice, this means: * The first grid value is located **half a cell size** away from the lower-left corner * Each grid point represents the center of a grid cell, not its corner This is the key point that often causes confusion. ---- **Effect on Visualization** Because grid values are defined at cell centers, the visualization behaves as follows: * The first cell is centered around its grid point * At the grid boundary, only **half of the first cell lies inside the grid extent** As a result: * The first grid cell appears visually as a **quarter cell** in the lower-left corner This is **not an error**, but a direct consequence of: - the grid origin being defined at the corner, and - the grid values being defined at cell centers. ---- **Illustration** The figure below illustrates this behavior: {{:cetrum_vs_lower_left_corner1_1.png?600|}} * Grid points are located at the **centers of the cells** * The grid origin is at the **lower-left corner** The first visible cell is therefore only partially shown This visual effect helps explain why the grid may appear “cut” at the edges.