Correct Answer - Option 4 : Secondary grid
Concepts:
Reference grids are used for accurate setting out of works of large magnitude. The following types of reference grids are used:
1. Survey Grid
2. Site Grid
3. Structural Grid
4. Secondary Grid
1. Survey grid is one, which is drawn on a survey plan from the original traverse. Original traverse stations form the control points of the grid.
2. Site grid is used by the designer with the help of which actual setting out is done. All the design points are related in terms of site grid coordinates.
3. Structural grid is used when the structural components of the building are large in numbers and are so positioned that these components cannot be set out from the site grid with sufficient accuracy. The structural grid is set out from the site grid points.
4. Secondary grid is established inside the structure, to establish internal details of the building, which are otherwise not visible directly from the structural grid.
