CHANGES IN THE COLUMNS AND ROWS, CELL SIZE AND THE EXTENT

In this dialogue box the data on the number of columns and rows, the cell size in X and Y and the extent of raster files can be displayed. It is possible to reach the dialogue box from many points within GeM+:

• Overview: Technical aspects
• Horizontal Spatial Reference System
• Extent

Furthermore, it is possible to enter the dialogue box when modifying the general data for a layer or the data for a specific band (depending on the option chosen in the radial button of the previous window). The title of the dialogue box tells us which option has been chosen since it indicates whether the data that are being displayed (and that may be changed depending on whether the option "read only" is activated or not) are the general data or whether they are data for a selected band. In the latter case the title also indicates which band. Naturally, for single band rasters the information for the layer and the band is the same.

In the box there are three Calculate buttons (for columns and rows, for cell sizes and for extents) that allow the corresponding parameters to be calculated (columns and rows, cell size or extents) based on the rest of the data in the box. If the entry for the parameter or parameters contains some previous value then, when the calculation is executed, this value is lost.

It is possible, and highly recommended, to force the cell sizes to be the same in both directions using the option x = y.

The Verify button checks that all the data are coherent with each other. (This is useful when making modification to various variables). This verification is always performed before leaving the dialogue box.

With the option Apply to all fields it is possible to extend the changes that the user makes to a value (whether for a specific band or the general value) to the rest of the fields or bands. If this option is marked then the values displayed in the box will become the values used by all the bands (fields) so that there will no longer be any particular values for any specific band (the values of all the fields will be the same and will equal the general value).

If this option is not marked the modifications made in the box will only affect the band in question. When changing the general data, the changes made will affect all those bands (fields) that had the same values as the general value (those bands without particular values). If any of the bands had particular values of any of the parameters (columns, rows, cell size or extent) then the changes are not applied to those bands.

Example: If a band has the general extent but twice the number of columns and rows than the general value (and therefore half the cell size), then the changes made to the general value will not affect the band.

The specific case of rasters in JPEG, JPEG2000 and MrSID format:

- The number of rows and columns of a JPEG file is shown by GeM+ but is never documented in the metadata because it is internal to the format itself and cannot be modified. For this reason the JPEG rasters never inherit the values of other fields even if the option "Apply to all fields" is activated. For the same reason, the general data of a layer made up of various JPEG files cannot be modified.

- In the case of a JPEG 24 bit color file (made up of three bands), all the bands are related and must have the same extent, cell size and number of columns and rows. For this reason when the values relating to one of the bands that makes up part of the JPEG 24 bit color file are changed then these changes are extended to all the bands automatically. In this case the title of the box indicates that all three bands are being modified together.