# Grid

### From ObjectVision

## Contents |

## **Introduction**

A grid is a two-dimensional data structure. A grid contains cells, defined by a row and a column number.

For images/pictures (think e.g. of bitmaps) only local row and column numbers are relevant.

In a GIS environment, a grid often represents a part of the world. Projection information is needed on how to interpret grid rows and columns in world coordinates, see paragraph: Geographic grids.

## **Grid functions**

Most functions in the GeoDMS work on data items of one (table) of two (grid) dimensional domains.

There is group of functions that explicitly use the two-dimensional structure of data in grids, for instance to calculate nearby relations. This group is called grid functions.

## **Geographic grids**

The GeoDMS can calculate with and visualize Geographic grid data.

To combine grids with other grid or vector data, they need refer to the same geographical coordinate system.

Grid data is related to a geographical coordinate system by it's domain unit (grid domain). This grid domain therefore needs to be aware of:

- the unit of the geographical coordinate system
- the projection information on how to interpret the relation of the grid domain (local coordinates) with the geographical coordinate system.

The following picture shows the relevant parameters of the projection information:

This projection information need to be configured as expression of the geographic grid domain unit. The parameters needed for this relation are (example values from grid domain in the RuimteScanner):

- pixel size in the x-direction in map units: 100
- pixel size in the y-direction in map units: -100
- x-coordinate of the center of the upper left pixel: 10.000
- y-coordinate of the center of the upper left pixel: 625.000

See RelateToGrid for more information on how to relate grids with other projections or vector data to a **grid** domain.