en-us http://www.bostongis.com Features the latest GIS tutorials on postgis, mapserver and other GIS technologies Boston GIS (mailto:articles@paragoncorporation.com) <h1>What is GDAL and RGDAL?</h1> <P>GDAL stands for Geospatial Data Abstraction Library and is a popular open source GIS library originally developed and maintained by <a href="home.gdal.org/warmerda/" target=_blank>Frank Warmerdam</a> with contributions http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut03 2008-03-14 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>ST_Translate, Translate</h1> <p>The ST_Translate function takes any geometry (linestring, multiline etc) returns a new geometry that is the original geometry moved by a vector defined by X,Y,Z. Note the units of measurement are always in the units http://www.bostongis.com/postgis_translate.snippet 2007-10-16 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>ST_Intersects, Intersects</h1> <P> ST_Intersects is a function that takes two geometries and returns true if any part of those geometries is shared between the 2. In PostGIS versions before 1.3 you would use the following syntax to utilize indexes < http://www.bostongis.com/postgis_intersection_intersects.snippet 2007-09-21 Paragon Corporation (mailto:support@paragoncorporation.com) <P>ST_Summary(geometry) gives you a brief summary of a geometry telling you how many simple geometries, rings and type of geometry it is. </P> <CODE> select ST_Summary(the_geom) from neighborhoods; </CODE> <b>Output of the above ran from psql looks like http://www.bostongis.com/postgis_st_summary.snippet 2007-08-24 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>A generic solution to PostGIS nearest neighbor</H1> <P>After some heavy brainstorming, I have come up with a faster and more generic solution to calculating nearest neighbors than my previous solutions. For the gory details on how I arrived at this s http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor_generic 2007-08-01 Paragon Corporation (mailto:support@paragoncorporation.com) <P>A common problem encountered in GIS is the Nearest Neighbor problem. In a nutshell the problem is to find the x number of nearest neighbors given a geometry and n geometries of data. </P> <P>The nearest neighbor crops up in other disciplines as wel http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor 2007-07-21 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>PL/R and PostGIS</h1> <p>In this tutorial we will explore using PostGIS and PL/R together. Some examples we will quickly run thru. <br> </p><ul><li>Median Function in conjunction with PostGIS</li> <li>Voronoi Diagrams</li> </ul> <p>If you mi http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut02 2007-06-20 Paragon Corporation (mailto:support@paragoncorporation.com) <p>R is both a language as well as an environment for doing statistical analysis. R is available as Free Software under the GPL. For those familiar with environments such as S, MatLab, and SAS - R serves the same purpose. It has powerful constructs for ma http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut01 2007-06-17 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>Creating Point Geometries with MakePoint</H1> <P>There are numerous ways of creating point geometries in PostGIS. We have covered these ways in other snippets. Check out the fulling links for other examples. </P> <UL> <LI><a href="postgis_geomfromt http://www.bostongis.com/postgis_makepoint.snippet 2007-06-02 Paragon Corporation (mailto:support@paragoncorporation.com) <P>In this tutorial we will just show some example snippets of using OpenLayers that we have found most useful. We will be assuming Open Layers 2.4 and above. </P> <h1>Initializing Layers Off</h1> In our previous example, you will notice that all the l http://www.bostongis.com/PrinterFriendly.aspx?content_name=openlayers_tut_02 2007-05-30 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>Loading Well-Known-Text (WKT) using PointFromText, LineFromText, MPointFromText, MLineFromText, MPolyFromText, PolyFromText</H1> <b>Syntax:</b> PointFromText(<i><a href="http://en.wikipedia.org/wiki/Well_Known_Text" target=_blank>wkt representation</a http://www.bostongis.com/postgis_pointfromtext_linefromtext_etc.snippet 2007-05-25 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>Extent Expand Buffer Distance ST_DWithin</h1> <P>In this quick exercise, we will explore the following PostGIS OGC functions: Extent, Expand, Buffer, Distance <br /> </P> <h2>Extent</h2> <P>Extent is an aggregate function - meaning that it is used jus http://www.bostongis.com/postgis_extent_expand_buffer_distance.snippet 2007-04-29 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>Simplify: Reduce the weight of a geometry</h1> <P>Simplify reduces the complexity and weight of a geometry using the <a href="http://geometryalgorithms.com/Archive/algorithm_0205/" target=_blank>Douglas-Peucker algorithm</a>. It in general reduces th http://www.bostongis.com/postgis_simplify.snippet 2007-04-26 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>GeomFromText: Loading a Geometry in Well-Known-text (WKT)) into PostGIS</h1> <P>The GeomFromText OGC function is used to convert a <a href="http://en.wikipedia.org/wiki/Well_Known_Text" target=_blank>Well Known Text (WKT) </a> version of a geometry in http://www.bostongis.com/postgis_geomfromtext.snippet 2007-04-25 Paragon Corporation (mailto:support@paragoncorporation.com) <P>ST_Makeline is an aggregate function that takes a sequence of points and strings them together to make a line. In versions of PostGIS prior to 1.2.2, this was called <i>MakeLine</i>. For prior versions - replace ST_MakeLine with MakeLine.</P> <h1>S http://www.bostongis.com/postgis_makeline.snippet 2007-04-23 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>OGR Tools</h1> <P>The OGR toolkit is a subkit of the FW Tools Toolkit. The FW Tools Toolkit is a toolkit available in both Linux and Windows executable form as well as source code form. It has several command line tools. The ones we find most usef http://www.bostongis.com/PrinterFriendly.aspx?content_name=ogr_cheatsheet 2007-03-28 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What is Open Layers?</h1> <P>Open Layers is an opensource client-side JavaScript/AJAX framework for overlaying various mapping services. It supports various mapping apis such as Google, Yahoo, Microsoft Virtual Earth, OGC WMS, OGC WFS, KaMap, Text l http://www.bostongis.com/PrinterFriendly.aspx?content_name=openlayers_tut_01 2007-01-02 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>The Fun Part: Mapping the Data</h1> <P>There are 5 key things we need to do when presenting data on web maps. They are <UL> <LI>Plotting the data</LI> <LI>Maintaining view state - where was the user last - if this is there first visit - initi http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_sharpmap_tut02 2006-11-02 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What is SharpMap</h1> <P>SharpMap is an opensource freely available mapping engine for the Microsoft.NET 2.0 Framework. It supports numerous datasources such as PostGIS, ESRI Shapefile, MSSQL Spatial, ECW and Oracle spatial. Future support is in the http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_sharpmap_tut01 2006-11-01 Paragon Corporation (mailto:support@paragoncorporation.com) <P>Often you will receive data in a non-spatial form such as comma delimited data with latitude and longitude fields. To take full advantage of PostGIS spatial abilities, you will want to create geometry fields in your new table and update that field usi http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut03 2006-09-09 Paragon Corporation (mailto:support@paragoncorporation.com)