Open Source Desktop GIS Solutions for the Not-So Casual User Roger C. Lowe III Warnell School of Forestry and Natural Resources The University of Georgia Athens, GA 30605 rlo@warnell.uga.edu Abstract Ask how to solve a given GIS task and you will receive a diverse suite of answers, many of which probably involve paging through predefined list of neatly packaged tools or the purchase of an extension for extended functionality and a new set of buttons to click or menu to browse. While commercial extensions offer a refined and integrated interface, their cost can be substantial and at times unaffordable. If you find your GIS software is lacking functionality, there is a good chance that there is a free and/or open source tool available that will meet your needs. I present below a brief review of several such tools I find useful in my daily GIS-related tasks. Keywords: Microsoft ICE, Google Refine, OSGeo, OSGeo4W, free GIS tools Introduction Many of us rely on commercial GIS software for our everyday analyses, map output, and reports. Most current releases offer a refined interface to numerous tools and features sufficient to address the daily tasks at hand though there are times when functionality is lacking for one reason or another. For example, the base licensing level of ESRI s ArcGIS software does not include the ability to simplify the boundaries of a polygon, the Smooth Polygon command, or to generate contours from an elevation model, the Contour command in the Spatial Analyst extension. Access to these functions requires either an upgrade in licensing or the purchase of an additional extension. For many, this is cost prohibitive, and with the availability of free tools that yield similar results, possibly an unneeded purchase. In this paper, I briefly describe a few of these free and/or open source software packages I use to fill in the functionality gap. Discussion Microsoft ICE Microsoft s Image Composite Editor (ICE) (Microsoft Corporation 2011), is a free tool that can be used to stitch a set of overlapping images into one large mosaic. Though its intended use is to generate a panorama from a series of photographs captured at a single camera location stationed In Proceedings of the 8 th Southern Forestry and Natural Resources GIS Conference (2012), K. Merry, P. Bettinger, T. Lowe, N. Nibbelink, and J. Siry, eds. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA.
Figure 1. Nine screen captures from the Clarke county QPublic site centered over the Whitehall Forest area. on the ground, it can also be used to stitch overlapping aerial photographs, multiple scans, or even a series of screen shots into seamless images. These mosaics can be imported into the GIS, georeferenced, and incorporated into your current workflow. For demonstration purposes, I generated a series of screen captures (Figure 1) from the Athens- Clarke county QPublic site (http://www.qpublic.net/clarke/) centered on the University of Georgia s Whitehall Forest area. The purpose of this internet mapping service is to provide a means to access public records in an online, spatially referenced context. Residents can search the site by property owner, tax parcel information, or by browsing a map. Once the target parcel is located, the user is provided the ability to pan and zoom, turn a predefined set of layers and labels on and off, and if zoomed in, display the parcel boundaries overlain on an aerial photograph. The QPublic site allows the user to export the map in PDF format; it does not provide a means to export the layers in a georeferenced, GIS-ready format. I use Microsoft ICE to stitch the individual images into one large mosaic which can then be georeferenced and used in the GIS. This workflow is more efficient than the alternative, georeferencing each individual image chip, and yields acceptable results.
Figure 2. Whitehall Forest screen captures after ICE processing. The only inputs required by ICE are a series of overlapping images. The stitched image from the Whitehall Forest example is shown in Figure 2. While the results are not perfect, there is slight misalignment along the northern road near the retaining pond; the process is relatively quick and the output image is suitable for rubbersheeting and inclusion as a base layer in the GIS. Tests using overlapping patterns of different colors failed, so color balancing may be necessary in processing individual scans of aerial photographs. Google Refine The underlying purpose of a geographic information system is to manage tabular data in a spatial context where information, possibly an owner s name or age, is linked to its spatial counterpart, the property boundary. When set up properly, numerous bits of information can be quickly symbolized, analyzed, reported on, and mapped. Clean and consistent data is critical for the successful implementation of such a system. Google Refine (Huynh 2010), currently maintained as one of Google s open source projects, assists in locating and correcting those inconsistencies
that will ultimately cause your system to fail. Google Refine quickly identifies and flags inconsistencies in naming conventions on a field by field basis. For example, addresses for properties located on Highway 32 in the 2009 Clarke county property sales database were listed as being on HWY 32, HWY32, Highway 32, Highway32, and highway 32 - the presence or absence of spaces are critical. The software identified all of these records as being the same road and provided an easy means of specifying a new descriptor for each. Complex entries like 59-245 & 73-11 and 73-11 & 59/245 where the difference is in more than just capitalization, abbreviations, and spaces were flagged as well. Caution should be taken, though, when evaluating fields containing dates. Entries that are obviously different, 1/16/2009 and 11/6/2009, are flagged as being the same. Before beginning with Google Refine, I recommend viewing the three short videos available from the project s home page. These videos cover the basics and will give you a good idea of the capabilities of this software. OSGeo & OSGeo4W The Open Source Geospatial Foundation (OSGeo) (OSGeo 2011a) was created to support the use and development of open source geospatial software. The group focuses on applications for web mapping, desktop mapping, and geospatial libraries. For users who desire easy installation, they offer a batch installer (OSGeo4W) (OSGeo 2011b) which can be used to install some or all of the software and libraries they support. On past projects, I have found the desktop applications Quantum GIS and gvsig to be valuable tools in my workflow. Through the Shapefile to PostGIS Import Tool, otherwise known as SPIT, Quantum GIS provides a graphical interface through which PostGIS layers can be quickly created and uploaded to a Postgresql database. Additional plugins, GdalTools and the Raster Terrain Analysis tool set, extend functionality for the import and analysis of raster layers not available in the base ArcGIS software. Users familiar with ArcView 3x may appreciate gvsig. It supports an extensive set of raster and vector analysis functionality, many of which are only available at ESRI s ArcInfo licensing level. The advanced functionality of these open source software matches, if not exceeds that of ESRI s ArcInfo. Though, they do fall short in two areas. Their feature labeling engines are nowhere near as feature-rich and the map layout and map creation capabilities are severely lacking when compared to those at any licensed level of ArcGIS. For these reasons, I still favor the map creation abilities provided by ESRI. Conclusion There are a wide range of free and open source software available that can be leveraged in a GIS environment. The Open Source Geospatial Foundation does a good job of promoting these tools, the user base is generally helpful, and installation is automated when using OSGeo4W. Functionality available in these software packages exceeds that of ESRI s base package, matches functionality of its advanced offering, and in situations when dealing with Postgres or MySQL databases, extends beyond it. On the other hand, these software packages do
not match ArcGIS labeling and map generation features. For this reason, it is improbable that one could migrate their entire GIS workflow to open source software. For users already working in an ESRI environment, I recommend using it to its fullest extent. When a situation does arise where functionality is lacking, I suggest giving these free and open source tools a try. References Huynh, D., and S. Mazzocchi. 2010. Google-refine Ver. 2.1-r216. Mountain View, CA: Google, Inc. http://code.google.com/p/google-refine/. Accessed 12 July 2011. Microsoft Corporation. 2011. Microsoft Image Composite Editor. Ver. 1.4.4.0. Redmond, WA: Microsoft Corporation. http://research.microsoft.com/enus/um/redmond/groups/ivm/ice/. Accessed 25 May 2011. OSGeo. 2011a. your open source compass. Beaverton, OR: Open Source Geospatial Foundation. http://www.osgeo.org/. Accessed 6 April 2012. OSGeo. 2011b. OSGeo4w, your open source compass for Windows. Beaverton, OR: Open Source Geospatial Foundation. http://trac.osgeo.org/osgeo4w/. Accessed August 2, 2011.