Georeferencing#

The georeferencing process uses the calibrated data cube and the navigation data to produce a geolocated data cube, taking into account various adjustments, offsets and interpolation methods.

Time offset to scan lines#

Exepected value: (optional) floating point value in seconds

This value provides a mechanism to account for a delay between scan line capture time and navigation data. The adjustment is applied to the scan line capture time, so a positive value moves forward through the navigation and negative value moves the data backwards along the navigation timeline.

Note

This field will be automatically set if you upload a Sensor Lookup File

Warning

An incorrect or missing value for this field is a common cause for poor quality results. Each Specim sensor is delivered with a sensor lookup file which defines this setting.

If you do not have the original lookup file or know the correct offset value, the best approach to take is to process a single flight line, ideally with clearly visible features of a known shape, for example a road or railway, using a range of values in this field. In some instances, the offset can be as much as 1 second, so starting with with 5 processing runs using values of 0.2, 0.4, 0.6, 0.8 and 1.0 would give an indication of which is closest. A visual examination of the quicklook image file will reveal which is the closest to the actual value, and additional processing runs with finer scale values will allow you reveal the actual value. This value is specific to a single sensor so, having done this process, you should record the value for future processing runs.

Sensor lever arm correction#

Exepcted values: (optional) three floating point values

If you are using an external navigation data source, these fields allow you to describe the offset between the position of the hyperspectral sensor and the IMU which delivers the navigation data.

Boresight correction#

Exepected values: (optional) three floating point values manually entered, or a calibration results file selected from the available list or dragged onto the orange dotted area.

The boresight correction values describe the offset from nadir of the instrument in relation to the aircraft. It is very hard to mount any sensor on any aircraft in such a way that it looks directly downwards. For the most accurate results from the processing operations, Geona Hyperspectral will make a correction for the difference between mounting angle/direction and nadir using the angles in floating point degrees provided.

If you have your own independently acquired boresight offset values enter them here as three distinct floating point values. If you do not have boresight offset values we strongly recommend you use the automated boresight calibration function to calculate these figures.

If you have already used the automatic boresight calibration function, please either select the results CSV file from the list or, if you have the file saved locally, drag and drop it into the orange dotted area. Either of these two methods will automatically populate the Roll, Pitch, and Heading fields.

See also

To calculate the boresight offset values, use the Boresight Calibration process - full details

Smooth the input data using a triangular filter#

Exepected value: (optional) an odd integer

This option allows some smoothing of data, which may be useful if it is very noisy. It applies a triangular filter to the data. The kernel is an odd number in length and the size should be entered here. This is typically only used if using poor quality real-time navigation data. The default action is to not do any smoothing.

Method of interpolation#

The navigation data can be interpolated using a linear or cubic spline method. The default is to use the linear method.

Position and Attitude data offset#

Expected value: (optional) floating point number

This allows you to apply a shift, in seconds, between the position and attitude data. In almost all cases this should not be used.

Use first sync message only#

Some Specim instruments output a sync message every second. By selecting this tickbox you disregard the multiple sync messages and only use the first one. This can be useful in cases where the frame rate (fps) is recorded incorrectly during data acquisition.