Python for Processing Digital Elevation Models

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This is a Python implementation of transforming, projecting and visualizing Digital Elevation Models as well as reading their elevation of given locations.

Table of Contents

• Terms and Abbreviations
• Functions
• DEM Data
  • ASTERGDEM
  • EUDEM
• Dependencies
• Pipeline of Processing ASTERGDEM
• Usage
  • Usage of ASTERGDEM
  • Usage of EUDEM
• Results
  • 2D DEM Images of London
  • Elevation of London
• References

Terms and Abbreviations

Term	Abbreviation	Remark
Digital Elevation Model	DEM	-
Geographic Coordinate System	GCS	[Longitude, Latitude, Elevation] on 3D ellipsoid
Projected Coordinate System	PCS	[X-coor, Y-coor, Elevation] on 2D plane
Georeferenced Tagged Image File Format	GeoTIFF	Data Format of DEM (e.g., .tif)
European Petroleum Survey Group	EPSG	EPSG codes identify different GCSs and PCSs
1984 World Geodetic System	WGS-84	GCS, EPSG-4326, approx. the ellipsoid of Earth
Pseudo Mercator (Web Mercator)	-	PCS of WGS-84, EPSG-3857
1936 Ordnance Survey Great Britain	OSGB-36	GCS, EPSG-4277, approx. the ellipsoid of Britain
British National Grid	BNG	PCS of OSGB-36, EPSG-27700
1989 European Terrestrial Reference System	ETRS-89	GCS, EPSG-4258, approx. the ellipsoid of Europe
Lambert Azimuthal Equal-Area	LAEA	PCS of ETRS-89, EPSG-3035

Functions

• Transforming DEM from one GCS (e.g., WGS-84) to another GCS (e.g., OSGB-36).

• Projecting DEM from one GCS (e.g., OSGB-36) to the related PCS (e.g., BNG).

• Converting DEM from one PCS (e.g., LAEA) to the related GCS (e.g., ETRS-89).

• Visualizing DEM in PCS as a 2D image.

• Reading the elevation of given locations from DEM in GCS.

DEM Data

ASTERGDEM

• ASTERGDEMv2.0 download link: https://earthexplorer.usgs.gov/

• See Introduction of ASTGDEMv20.pdf for detailed introduction and user guide (recommended).

EUDEM

• EUDEMv1.1 download link: https://land.copernicus.eu/imagery-in-situ/eu-dem/eu-dem-v1.1

• See here for detailed introduction and user guide.

Dependencies

• gdal (osgeo) 1.11.3
• matplotlib 3.0.2
• numpy 1.15.4
• pandas 0.23.4

The following procedures (1-2) for installing GDAL are recapitulated from mothergeo.

1. Install GDAL Development Libraries and export environment variables for the compiler in Terminal.

$ sudo apt-get install libgdal-dev

$ export CPLUS_INCLUDE_PATH=/usr/include/gdal
$ export C_INCLUDE_PATH=/usr/include/gdal

2. Install GDAL Python Libraries in Terminal.

$ pip install GDAL

If it comes with the error: cpl_vsi_error.h: No such file or directory, please try the following procedures.

3. Check the required version of GDAL Python Libraries in Terminal.

$ gdal-config --version

4. Download the source file (e.g., gdal-1.11.3.tar.gz) of the related GDAL version (e.g., 1.11.3) from here.

5. Manually install GDAL Python Libraries in Terminal.

$ cd path/of/downloaded/gdal/package

~$ tar -xvzf gdal-{VERSION}.tar.gz
# E.g., ~$ tar -xvzf gdal-1.11.3.tar.gz

~$ cd extracted/gdal/folder
# E.g., ~$ cd gdal-1.11.3

~$ cd swig
~$ cd python
# The setup.py exists in this directory.

~$ python setup.py build_ext --include-dirs=/usr/include/gdal/
~$ python setup.py install

6. Run >>> from osgeo import gdal in Python. If no error occurs, the installation is accomplished.

Pipeline of Processing ASTERGDEM

Usage

The directory of source DEMs is shown in the following figure.

Usage of ASTERGDEM

1. Download DEMs ASTGTM2_N51W001_dem.tif and ASTGTM2_N51E000_dem.tif from here.

2. Copy DEMs to the folder DATA/DATA_ASTGDEMv20/EPSG4326_s/.

3. To process ASTREGDEMv2.0 DEMs, run run_DEM_ASTGDEMv20.py or run_DEM_ASTGDEMv20.ipynb.

4. The log of running run_DEM_ASTGDEMv20.py can be seen in Log_run_DEM_ASTGDEMv20.txt.

Usage of EUDEM

1. Download DEM eu_dem_v11_E30N30.tif from here.

2. Copy DEM to the folder DATA/DATA_EUDEMv11/ and rename it as EUDEMv11_EPSG3035.tif.

3. To process EUDEMv1.1 DEM, run run_DEM_EUDEMv11.py or run_DEM_EUDEMv11.ipynb.

4. The log of running run_DEM_EUDEMv11.py can be seen in Log_run_DEM_EUDEMv11.txt.

Results

2D DEM Images of London

• The 2D DEM Image of ASTERGDEMv2.0 in Pseudo Mercator PCS

• The 2D DEM Image of ASTERGDEMv2.0 in BNG PCS

• The 2D DEM Image of ASTERGDEMv2.0 in LAEA PCS

Elevation of London

• The elevation of 24 locations in London (meters)

No. of Location	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24
ASTGDEMv20_WD	18	18	38	40	65	26	35	31	17	79	13	41	62	82	9	13	31	31	15	22	24	40	8	40
ASTGDEMv20_UK	14	14	36	25	60	37	33	40	20	68	12	25	62	59	15	18	22	22	15	21	14	33	8	47
ASTGDEMv20_EU	18	18	38	40	65	26	35	31	17	79	13	41	62	82	9	13	31	31	15	22	24	40	8	40
EUDEMv11_WD	12	12	37	30	61	25	29	36	11	66	11	31	64	79	7	27	25	25	14	15	13	32	5	36
EUDEMv11_UK	12	12	37	26	58	30	32	35	11	71	8	30	66	78	8	26	24	24	8	16	13	32	9	35
EUDEMv11_EU	12	12	37	30	61	25	29	36	11	66	11	31	64	79	7	27	25	25	14	15	13	32	5	36

References

[1] EPSG 4326 vs EPSG 3857 (projections, datums, coordinate systems, and more!)

[2] Coordinate systems and projections for beginners

[3] CSDN Blog

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