Manipulating Spatial Data using Open Source Tools

George Wright, OceanWise

Introduction

A common way to manipulate spatial data is through the use of GIS, which is not without its drawbacks. 

  • Limited process memory
  • Batch processing is difficult
  • May require licensed extensions
  • Requires use of proprietary formats
  • Limited options
  • Expensive

Existing solutions

FME

Global Mapper

ESRI ModelBuilder

FME

Global Mapper

ESRI ModelBuider

What do you really need?

GDAL/OGR Tools

Geospatial Data Abstraction Library (GDAL)

 

OpenGIS Simple Features Reference Implementation (OGR)

 

In late 1998, Frank Warmerdam started work on the GDAL/OGR library

Library for reading/writing raster and vector geospatial data formats

 

Distributed under the terms of ​X11/​MIT License

 

Supported on all modern ​flavors of Unix and most versions of ​Microsoft Windows.

Why use these tools?

  • V 2.x unification of GDAL and OGR libraries and more
  • Regularly updated with new features
  • Bundled with QGIS out the (free) box
  • Integrates with Python 

 

import gdal, ogr, osr

Driving GDAL/OGR

Tools are driven from the command line, there is no user interface! Now this might take some getting used to.

Create a VRT from XYZ

<OGRVRTDataSource>
    <OGRVRTLayer name="dem">
        <SrcDataSource>dem.csv</SrcDataSource>
        <GeometryType>wkbPoint</GeometryType>
        <GeometryField encoding="PointFromColumns" x="X" y="Y" z="Z"/>
    </OGRVRTLayer>
</OGRVRTDataSource>
gdalbuildvrt dem.txt dem.vrt

XYZ Soundings to GRID

gdal_grid -l dem dem.vrt dem.tif

GRID to Contour Model

gdal_contour -f "GML" -a DEPCNT -i 0.5 -nln data dem.tif contours.gml

Applying the technology

How OceanWise harness GDAL/OGR tools

Supporting Formats

By embedding the GDAL/OGR drivers into our internal data processing tools we are able to save time and money whilst supporting a huge variety of Raster/Vector formats and the entire proj4 coordinate reference system library!

Processing large datasets

Bathymetric datasets are an example of Maritime data which is constantly increasing in size. Most programs, GIS included, won't allow you to load more than 4GB of data.

 

What do you do when you're handed a large bathymetric dataset to build with a contour model?

Raster Charts XL

Alternatives

  • QGIS - An open source GIS that uses the OGR and GDAL libraries to view several vector and raster formats, and includes support for PostGIS tables and GRASS digitizing.
  • OpenLayers - A pure JavaScript library for displaying map data in most modern web browsers, with no server-side dependencies. OpenLayers implements a JavaScript API for building rich web-based geographic applications.
  • Shapely -  Python package for manipulation and analysis of planar geometric objects.

Thank you for listening.

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