Geoprocessing with GDAL and Numpy in Python

Delong Zhao11-03-2011

Geoprocessing with GDAL and Numpy in Python

• GDAL - Geospatial Data Abstraction Library• Numpy - the N-dimensional array package for

scientific computing with Python. • Both of them are open source software

Read raster dataset using

GDAL

Do some calculation using

Numpy

Output to geospatial dataset using GDAL

GDAL

• Supports about 100 raster formats– ArcInfo grids, ArcSDE raster, Imagine, Idrisi, – ENVI, GRASS, GeoTIFF– HDF4, HDF5– USGS DOQ, USGS DEM– ECW, MrSID– TIFF, JPEG, JPEG2000, PNG, GIF, BMP– See http://www.gdal.org/formats_list.html

Numpy

• the fundamental package needed for scientific computing with Python.

• a powerful N-dimensional array object• sophisticated (broadcasting) functions• tools for integrating C/C++ and Fortran code• useful linear algebra, Fourier transform, and

random number capabilities.• http://numpy.scipy.org/

Installation

• 1. Enthought python scientific computing package, includes numpy– http://www.enthought.com/

• 2. GDAL - Geospatial Data Abstraction Library– http://www.lfd.uci.edu/~gohlke/pythonlibs/

• Or all of these has been installed on EOMF and Cybercommons servers

Tutorial

• http://itmetr.net/itmetr.cgi/PyIntro• http://www.gis.usu.edu/~chrisg/python/2009

/• http://www.scipy.org/NumPy_for_Matlab_Us

ers• https://www.cfa.harvard.edu/~jbattat/comput

er/python/science/idl-numpy.html

Sample 1

• Read two tif files (red band and nir band)• Calculate

• Output NDVI in same projection and georeference as the input file.

• Numpy example

Algorithm development for global cropping intensity from 2000-2011

1-crop per year2-crop per year

3-crop per year

(b) 6/11/99 rice field preparation

(c) 7/3/99 2-weeks after rice transplanting

(d) 9/6/99 rice plant heading

Dynamics of winter wheat and paddy rice fields in Nanjing, Jiangsu, China

Field site in Jiangsu

Time (8-day interval)

1/1/02 3/1/02 5/1/02 7/1/02 9/1/02 11/1/02 1/1/03

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winter wheat paddy rice

MODIS 8-day composites of surface reflectance product (MOD09A1)

NDSI NDVI, EVI, LSWI

Snow mask

Cloud mask Permanent water mask

Evergreen vegetation mask

Cropping intensity ( # of crops per year)

Crop calendar (planting & harvesting dates)

Inundation and paddy rice

Temporal profile analysis of individual pixels

one MODIS pixel in Bangkok area

Month in 2004

1 2 3 4 5 6 7 8 9 10 11 12

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Starting date Starting date

One MODIS pixel in Mekong basin

Month in 2004

1 2 3 4 5 6 7 8 9 10 11 12

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flooding &transplanting

flooding &transplanting

flooding &transplanting

Cropping Intensity map in 2004

Global Mapping of Croplands

Python multiprocessing

• http://docs.python.org/library/multiprocessing.html

• import multiprocessing• pool = multiprocessing.Pool(processes=multiprocessing.cpu_count())• pool.map(doprocess,findfiles(root_dir))

Benchmark

• I did some benchmark. By using all 8 cpu and 16G memory on one eomf server

• can finish 1 MODIS tile NDVI, EVI, CLOUD,SNOW, LANDWATER, FLOOD, Drought products in 15 minutes.

• This means we can finish global 296 tiles 2000-2011 MODIS data in 786 hours (32 days) with one server.

• And we have 6 computation servers, we can improve it to 6 days if all the servers can do the job.