<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Ah the heart of all knowledge... Philosophy!<div><br><div><div>On 3-Apr-09, at 10:24 AM, Paul Ramsey wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Philosophical point:<br><br>Creating a column and filling it with a property of GEOMETRY like<br>ST_Area() or ST_Length() is something which makes sense in a legacy<br>GIS like Arc* or GRASS, where attributes are handled separately from<br>spatial. In a spatial database, where the GEOMETRY is co-equal to the<br>other columns, there is not much point, unless you are doing it for<br>export purposes (filling in a column before exporting to shapefile for<br>consumption by a legacy GIS).<br><br>What does having AREA in a column gain you? Now you can do math and<br>tests against it? Well, in database land, you can do that already,<br>just do you math and tests against the ST_Area() function directly.<br><br>Paul<br></div></blockquote><div><br></div><div>Hmmm point taken, and I understand the logic behind the argument is absolutely sound, why fill a database with endless amounts of attributes that are simply the results of calculations which in theory can me quickly and dynamically calculated to it's present values. Hydrological processes, and networking are a good example of this where temporal changes occur to values.</div><div><br></div><div>However, there are instances where information is static within the realm of a human timescape. In these instances where is the worth in constantly calculating the value of 10 x 10 when we can easily store it to memory as 100 and do a simple read?</div><div><br></div><div>Legacy or not, certain values are well represented as a static attribute while others sensitive to dynamics are best suited as you mention to dynamic testing.</div><div><br></div><div>In my case I simply wish to: </div><div><br></div><ul class="MailOutline"><li>Receive information from gov data (usually in shapefile format)</li><li>Add to postgreSQL/postGIS database </li><li>Manipulate for end user visualization and reference</li><li>Export to KML for easy desktop viewing and web viewing for non-technical users. </li></ul><div><br></div><div>=====</div><div><br></div><div>I think I am starting to get the hang of pgAdmin, I'm busy reprogramming my brain for these new tools.</div><div><br></div><div>Mars</div><div><br></div><blockquote type="cite"><div><blockquote type="cite">Hello Aurora,<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">In ArcGIS it's all different. In PostGIS you can use simple/complex SQL<br></blockquote><blockquote type="cite">queries to "calculate values" in a similar fashion of arcgis.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">The simplest of them all would be, in your case:<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">ALTER TABLE table1 ADD COLUMN area_column double precision;<br></blockquote><blockquote type="cite">UPDATE table1 SET area_column = ST_AREA(the_geom);<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">You can in that SQL query divide, multiply, and do whatever you want with<br></blockquote><blockquote type="cite">that result that will be written to the column area_column.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I hope that helps<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">George<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">On Fri, Apr 3, 2009 at 12:55 PM, Aurora Geomatics<br></blockquote><blockquote type="cite"><<a href="mailto:aurorageomatics@gmail.com">aurorageomatics@gmail.com</a>> wrote:<br></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Hello PostGIS users,<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">I have just installed William Kyng's PostgeSQ/PostGIS packages for Mac OS<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">X.5<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">I have been playing with pgAdmin and QGIS with importing shapefiles into<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">PostGIS. Works dandy.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Now I am wondering how to solve Attribute Calculations.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Years of using ArcGIS and GRASS it is pretty straightforward on those<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">apps, and am stumped with PostGIS Attribute calculations..<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">For example, using a polygon feature;<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Creating a new column, say AREA and filling with a calculation that is<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Hectares.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Thanks!</blockquote></blockquote></div></blockquote></div><br></div></body></html>