mchailey / hytools-sandbox

HyTools

HyTools is a python library for working with imaging spectroscopy data, with a focus on terrestrial scenes. At it's core it consists of a series of functions for reading and writing ENVI-formatted images in addition to opening NEON-formatted AOP HDF files. Built on top of these functions are a series of higher level processing tools for data analysis which include spectral resampling, topographic correction and BRDF correction. Other features are currently under development and include mask generation and MNF transformation.

We have also created a series of command line tools which string together the processing functions and provide a more streamlined workflow for processing images.

Dependencies

• numpy
• h5py
• gdal

Basic usage

import hytools as ht

#Read an ENVI file
hyObj = ht.openENVI('envi_file.bin')
#Map image data to numpy memmap object
hyObj.load_data()

#Calculate NDVI, retrieves closest wavelength to input lambda in nm
ir = hyObj.get_wave(900)
red = hyObj.get_wave(660)
ndvi = (ir-red)/(ir+red)

#Other options for retrieving data
band = hyObj.get_band(10)
column = hyObj.get_column(1)
line = hyObj.get_line(234)
chunk = hyObj.get_chunk(x1,x2,y1,y2)

# Create a writer object to write to new file
writer = ht.file_io.writeENVI('output_envi.bin',hyObj.header_dict)

#Create an iterator object to cycle though image
iterator = hyObj.iterate(by = 'line')

# Cycle line by line, read from original data
while not iterator.complete:  
   #Read next line
   line = iterator.read_next() 

   #Do some calculations.......
   radiance = line * gain + offset

   #Write line to file
   writer.write_line(radiance,iterator.current_line)
	
writer.close()  

Examples

BRDF Correction

The BRDF correction module consists of a series of tools for removing brightness gradients caused by variation in solar and viewing geometry. The module uses the combination of the Ross and Li kernels to model the volumetric, geometric and isometric scattering surfaces and applies a multiplicative correction to remove brightness gradients.

Topographic Correction

The topographic correction module uses the Sun-Canopy-Sensor (SCS+C) method developed by Soenen et al. 2005 to remove shadows caused by variation in topography.