Topographic and tectonic stress inversions with halfspace: Preparing a DEM

In order to complete the tutorial, please first clone/download the github repo which comes with the DEM, coseismic slip model, and some auxiliary files, all with the correct pathnames.

( Or just download this notebook )

This is a brief step that simply involves reading and flipping a DEM. DEMs in GeoTIFF format are referenced differently, with the origin at the upper left. We will also get some of the projection metadata from the DEM.

In[1]:

# inline plotting %matplotlib inline %config InlineBackend.figure_format = 'retina'

In[2]:

from __future__ import division import gdal import numpy as np import matplotlib.pyplot as plt import json import pyproj as pj

In[3]:

# open dataset in gdal dem_dataset = gdal.Open('../test_data/dem/baloch_500m_wide_utm41n.tif')

The dem_dataset is a container class, with various methods for reading data and metadata. No data has been read yet.

We will use the GetGeoTransform() method to read in the metadata as a tuple.

In[4]:

dem_dataset.GetGeoTransform()

Out[4]:

(398285.44218398223, 445.9049868175545, 0.0, 3329810.0066404096, 0.0, -445.9049868175547)

In[5]:

dem_dataset.RasterXSize, dem_dataset.RasterYSize

Out[5]:

(1371, 1516)

Write GeoTransform parameters to dictionary

python dictionaries can be saved as JSON text files, which are widely used and also much easier to work with than similar files like XML. Additionally, it is very easy to read JSON files back into Python dictionaries, which makes them ideal for metadata and configuration files.

In[6]: # write GeoTransform parameters to dictionary dem_transform = {'upper_left_x': dem_dataset.GetGeoTransform()[0], 'x_res_m' : dem_dataset.GetGeoTransform()[1], 'x_rotation': dem_dataset.GetGeoTransform()[2], 'upper_left_y': dem_dataset.GetGeoTransform()[3], 'y_rotation': dem_dataset.GetGeoTransform()[4], 'y_res_m': dem_dataset.GetGeoTransform()[5], 'n_cols': dem_dataset.RasterXSize, 'n_rows': dem_dataset.RasterYSize} dem_transform['y_res_m'] *= -1 # correct for the upper-left origin thing print(dem_transform)

{'y_res_m': 445.9049868175547, 'n_cols': 1371, 'upper_left_x': 398285.44218398223, 'upper_left_y': 3329810.0066404096, 'x_rotation': 0.0, 'x_res_m': 445.9049868175545, 'n_rows': 1516, 'y_rotation': 0.0}

Now let's add some other metadata which will come in handy.

In[7]: dem_transform['east_min'] = dem_transform['upper_left_x'] dem_transform['east_max'] = (dem_transform['x_res_m'] * dem_transform['n_cols'] + dem_transform['east_min']) dem_transform['north_max'] = dem_transform['upper_left_y'] dem_transform['north_min'] = (-1 * dem_transform['y_res_m'] * dem_transform['n_rows'] + dem_transform['north_max']) In[8]: # get latitude and longitude for the corners of the array, just 'cause. wgs84 = pj.Proj(init='epsg:4326') utm41n = pj.Proj(init='epsg:32641') dem_transform['lon_min'], dem_transform['lat_min'] = pj.transform(utm41n, wgs84, dem_transform['east_min'], dem_transform['north_min']) dem_transform['lon_max'], dem_transform['lat_max'] = pj.transform(utm41n, wgs84, dem_transform['east_max'], dem_transform['north_max']) In[9]: # save metadata dictionary to file with open('../test_da