Tag Archives: multispectral

Visualising Philip Island

One objective (amongst many) that Chris and I have identified is to first start off looking at islands. The reason behind this is simple: an island presents a defined and constrained geographic area – not too big, not too small (depending on the island, of course) – and I’ve had a lot of recent experience working with island data on my recent Macquarie Island project with my colleague Dr Gina Moore. It provides some practical limits to the amount of data we have to work with, whilst engaging many of the technical issues one might have to address.

With this in mind, we’ve started looking a Philip Island (near Melbourne, Victoria) and Kangaroo Island (South Australia). Both fall under a number of satellite paths, from which we can isolate multispectral and hyperspectral data. I’ll add some details about these in a later post – as there are clearly issues around access and rights that need to be absorbed, explored and understood.

For a first attempt, here is a google colab script for looking at some Philip Island data from the XXX Satellite:

# Import necessary libraries
import os
from osgeo import gdal, gdal_array
from google.colab import drive
import numpy as np
import matplotlib.pyplot as plt
# Mount Google Drive
#this will ask for permissions - you will need to login through your google account in a pop-up window
# Open the multispectral GeoTIFF file
#set the file path to the folder with the relevant data in it on your google drive (mount this first via the panel to the left of this one - it is called 'drive' and appears as a folder)
file_path = '/content/drive/MyDrive/DATA/XXX_multispectral.tif'
#set a variable for your path and the file you open
src_ds = gdal.Open(file_path)
#use gdal to get some characteristics of the data in the file
print("Projection: ", src_ds.GetProjection())  # get projection
print("Columns:", src_ds.RasterXSize)  # number of columns
print("Rows:", src_ds.RasterYSize)  # number of rows
print("Band count:", src_ds.RasterCount)  # number of bands
print("GeoTransform", src_ds.GetGeoTransform()) #affine transform
# Use gdalinfo command to print and save information about the raster file - this is extracted from the geotiff itself
info = gdal.Info(file_path)
if not os.path.exists("/content/drive/MyDrive/DATA/OUTPUT"):
info_file = os.path.join("/content/drive/MyDrive/DATA/OUTPUT", "raster_info.txt")
with open(info_file, "w") as f:
# Retrieve the band count and band metadata
data_array = src_ds.GetRasterBand(1).ReadAsArray()
band_count = src_ds.RasterCount
# Loop through each band and display in a matplotlib image
for i in range(1, band_count+1):
    band = src_ds.GetRasterBand(i)
    minval, maxval = band.ComputeRasterMinMax()
    data_array = band.ReadAsArray()
    plt.figure(figsize=(16, 9))
    plt.imshow(data_array, vmin=minval, vmax=maxval)
    plt.colorbar(anchor=(0, 0.3), shrink=0.5)
    plt.title("Band {} Data\n Min value: {} Max value: {}".format(i, minval, maxval))
    plt.suptitle("Raster data information")
    band_description = band.GetDescription()
    metadata = band.GetMetadata_Dict()
    geotransform = src_ds.GetGeoTransform()
    top_left_x = geotransform[0]
    top_left_y = geotransform[3]
    w_e_pixel_res = geotransform[1]
    n_s_pixel_res = geotransform[5]
    x_size = src_ds.RasterXSize
    y_size = src_ds.RasterYSize
    bottom_right_x = top_left_x + (w_e_pixel_res * x_size)
    bottom_right_y = top_left_y + (n_s_pixel_res * y_size)
    coordinates = ["Top left corner: ({},{})".format(top_left_x,top_left_y),"Bottom right corner:({},{})".format(bottom_right_x,bottom_right_y)]
    if band_description:
        metadata_list = ["Band description: {}".format(band_description)]
        metadata_list = ["Band description is not available"]
    if metadata:
        metadata_list += ["{}: {}".format(k, v) for k, v in metadata.items()]
        metadata_list += ["Metadata is not available"]
    plt.annotate("\n".join(coordinates+metadata_list), (0,0), (0, -50), xycoords='axes fraction', textcoords='offset points', va='top')
    plt.savefig("/content/drive/MyDrive/DATA/OUTPUT/Band_{}_Data.png".format(i), vmin=minval, vmax=maxval)


This works well enough for a plot – but it’s interesting (a debate) – whether it is best/easiest to use GDAL or the rasterio Mapbox wrapper. Tests will tell. And there is Pandas too. They all have pros and cons. Try it yourself and let us know,

I’m looking into ways of sharing the colabs more directly for those who are interested – that’s the whole point.