# Geometric function

The Geometric process produces an orthorectified image based on a sensor definition and a terrain model.

To learn about orthorectification, see Fundamentals of orthorectifying a raster dataset.

The inputs for this function are the following:

• Input Raster
• Constant Z
• DEM

You can use this function when your raster data has rational polynomial coefficients (RPCs). If you don't have a digital elevation model (DEM), you can specify the Constant Z value. If you have a DEM, check the Use DEM check box.

## When using a DEM

You can use a DEM contained within the mosaic dataset, or one stored in a raster catalog, as a raster dataset, or a mosaic dataset who's output is a DEM.

### Z Factor

The scaling factor used to convert the elevation values. The scaling factor is used for two purposes: first, to convert the elevation units (such as meters or feet) to the horizontal coordinate units of the dataset, which may be feet, meters, or degrees, and second, to add vertical exaggeration for visual effect.

To convert from feet to meters or vice versa, see the table below. For example, if your DEM's elevation units are feet and your mosaic dataset's units are meters, you would use a value of 0.3048 to convert your elevation units from feet to meters (1 foot = 0.3048 meters).

This is also useful when you have geographic data (such as DTED in GCS_WGS 84 using latitude and longitude coordinates) where the elevation units are in meters. In this case, you need to convert from meters to degrees (0.00001; see below). The value for degree conversions are approximations.

Units conversion factor

From

To

Feet

Meters

Degrees

Feet

1

0.3048

0.000003

Meters

3.28084

1

0.00001

Units conversion factor

To apply vertical exaggeration, you must multiply the conversion factor by the exaggeration factor. For example, if both elevation and dataset coordinates are meters and you want to exaggerate by a multiple of 10, the scaling factor would be unit conversion factor (1.0 from the table) multiplied by the vertical exaggeration factor (10.0), or 10. As another example, if the elevations are meters and the dataset is geographic (degrees), you would multiply the units conversion factor (0.00001) by 10 to get 0.0001.

### Z Offset

The base value to be added to the elevation value in the DEM. This could be used to offset elevation values that do not start at sea level.

### Geoid

Check the Geoid check box if you would like the orthocorrection process to assume the earth is a geoid and not a sphere. This will apply the geoid (EGM96) correction to the z values.

## Validating the Geodata Transform

If you click the Geodata Transform button, this will open a window displaying the information specific to the geometric transformation that will be applied to the raster data.

8/21/2013