Getting reference spectrum from EVM

Hi Cheery,

It may help if I provide some additional background information. The following is present in the doxygen documentation scan module overview of the Spectrum Library:

Interpret reference

Most spectroscopy analysis is performed as material absorbance, reflectance, or transmittance. This references out any difference in radiometric response between two different instruments, and instead characterizes the properties of the sample being measured independent of the instrument. This process involves scanning a reference with a neutral reflector in the case of reflectance, or a null sample in the case of transmittance. Since a DLP spectrometer can have many different programmable scan configurations, the data from this reference measurement can vary depending on the scan configuration due to wavelength and pattern size dependent diffraction efficiencies.

In applications where a reference is not readily available or it is not desired to retake a reference scan, this library provides the dlpspec_scan_interpReference() function to model what the reference would measure for a new scan configuration with only that configuration data and a previous reference scan serialized uScanData blob. This can be used with previous scans stored on the client, or it can be used in combination with a previous reference stored on the DLP spectrometer.

To do this modeling, the dlpspec_scan_interpReference() function uses the following parameters, as displayed in the doxygen documentation:

The above parameters correspond to the following data file types from the NIRscan Nano:

• pRefCal/size: NNO_FILE_REF_CAL_COEFF, just how you described, or by using EVM::FetchRefCalData in the evm class.
• pMatrix/size: NNO_FILE_REF_CAL_MATRIX, just how you described, or by using EVM::FetchRefCalMatrix in the evm class.
• pScanResults: Acquire scan data from the following (you are likely already doing this while fetching scan data):

• size = NNO_GetFileSizeToRead(NNO_FILE_SCAN_DATA);
• allocate buffer
• NNO_GetFile(buffer, size);
• allocate scan_results (scanResults structure)
• dlpspec_scan_interpret(buffer, size, &scan_results);

• pRefResults: newly allocated scanResults structure.

After calling dlpspec_scan_interpReference() with the above parameters, you will have two pointers to interpreted scanResults structures:

• &scan_results
• pRefResults

The wavelength vectors in both of these scanResults structures will be identical, and you may divide &scan_results->intensity[] by pRefResults->intensity[] to yield transmission or reflectance depending on the sampling method used. Taking the negative log10 of the transmission or reflectance as shown in section 5.1.8.5 of the user's guide will yield absorbance.