Postgres OnLine Journal - application development

Saying Happy Valentine in PostGIS

nospam@example.com (Leo Hsu and Regina Obe) — Thu, 14 Feb 2013 02:44:00 -0500

A while back I mentioned to Bborie (aka dustymugs) and Sandro (aka strk): We're missing ability to label our images with text. Picture this: What if someone has got a road or a parcel of land and they want to stamp the parcel id or the road name on it and they don't want to have to depend on some piece of mapping software. Many report writers and databases can talk to each other directly such as we demonstrated in Rendering PostGIS raster graphics with LibreOffice and we've got raster functionality in the database already. Can we cut out the middleman? Some ideas came to mind. One we could embed a font lib into PostGIS thus having the ultimate bloatware minus the built-in coffee maker. strk screeched. He's still recovering from my constant demands of having him upgrade his PostgreSQL version. Okay fair enough.

Bborie suggested why don't you import your letters as rasters and then vectorize them. So that's exactly what we are going to demonstrate in this article and in doing so we will combine some of the new features coming in PostGIS 2.1 we've been talking about in Waiting for PostGIS 2.1 series.

Warning this article will have a hint of Rube Goldbergishness in it. If you are easily offended by seeing stupid tricks done with SQL, stop reading now. We are going to take a natural vector product and rasterize it just so we can vectorize it again so we can then rasterize it again. Don't think about it too much. It may trigger activity in parts of your brain you didn't know were there thus resulting in stabbing pains similar to what you experience by quickly guplping down a handful of Wasabi peas.

So here are the steps for creating your own font set you can overlay on your geometries and rasters.

See if you can spot the use of window functions and CTEs in these examples.

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Creating GeoJSON Feature Collections with JSON and PostGIS functions

nospam@example.com (Leo Hsu and Regina Obe) — Fri, 24 Aug 2012 02:55:00 -0400

If you do a lot of web-based GIS applications, a common desire is to allow a user to draw out an area on the map and then do searches against that area and return back a FeatureCollection where each feature is composed of a geometry and attributes about that feature. In the past the format was GML or KML, but the world seems to be moving to prefer JSON/GeoJSON. Normally you'd throw a mapping server that talks Web Feature Service , do more or less with a webscripting glue, or use a Webservice such as CartoDb that lets you pass along raw SQL.

In this article we'll demonstrate how to build GeoJSON feature collections that can be consumed by web mapping apps. using the built in JSON functions in PostgreSQL 9.2 and some PostGIS hugging. Even if you don't use PostGIS, we hope you'll come away with some techniques for working with PostgreSQL extended types and also how to morph relational data into JSON buckets.

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PLV8JS and PLCoffee Part 2B: PHP JQuery App

nospam@example.com (Leo Hsu and Regina Obe) — Fri, 10 Aug 2012 13:32:00 -0400

In our last article, PL/V8JS and PL/Coffee JSON search requests we demonstrated how to create a PostgreSQL PL/Javascript stored function that takes as input, a json wrapped search request. We generated the search request using PostgreSQL. As mentioned, in practice, the json search request would be generated by a client side javascript API such as JQuery. This time we'll put our stored function to use in a real web app built using PHP and JQuery. The PHP part is fairly minimalistic just involving a call to the database and return a single row back. Normally we use a database abstraction layer such as ADODB or PearDB, but this is so simple that we are just going to use the raw PHP PostgreSQL connection library directly. This example requires PHP 5.1+ since it uses the pg_query_param function introduced in PHP 5.1. Most of the work is happening in the JQuery client side tier and the database part we already saw. That said the PHP part is fairly trivial to swap out with something like ASP.NET and most other web server side languages.

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Rendering PostGIS Raster graphics with LibreOffice Base Reports

nospam@example.com (Leo Hsu and Regina Obe) — Fri, 17 Feb 2012 18:21:00 -0500

I was excited to learn from Pasha Golub's blog LibreOffice Base 3.5 now comes packaged with native PostgreSQL driver so no separate configuration is required. The connection string syntax follows the old SBC native driver of prior OpenOffice versions we itemized in Using OpenOffice Base with PostgeSQL.

What I really wanted to do with it is experiment with its graphical rendering capabilities. As discussed in PSQL needs a better way of outputting bytea one of the frequently asked questions on the PostGIS list by folks using the new not yet officially released (alpha5 recently released) functionality in PostGIS 2.0 is how to render rasters with common variety tools. I suspected Base was a capable option, but had never tested it to confirm. Since I was installing new LibreOffice 3.5, I thought this might be a good test of its metal.

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PostGIS as a graphical engine

nospam@example.com (Leo Hsu and Regina Obe) — Fri, 26 Aug 2011 18:50:00 -0400

A while back in New Additions and Promotions in PostGIS Development Team, I mentioned that the new addition to our team Bborie Park was working on image output functions for raster support, among other things. His last addition was ST_AsRaster which allows a PostGIS geometry to cross the line to the raster world, all in the database. This new addition almost completes the basic cycle of making PostGIS not only a spatial analytical tool, but also a rendering engine.

To test out these new functions, I whipped up a quick ASP.NET/JQuery app as described in Minimalist Web-based ASP.NET PostGIS 2.0 Spatial Geometry/Raster Viewer, and Bborie followed up with the PHP version which you can download from http://www.postgis.us/downloads/postgis_webviewer_php.zip.

There is still much room for improvement, e.g. intersection of 2 rasters, faster response, etc, but I can see all the lights flickering and the connections coming together like a self-orchestrating organism. From chaos comes order.

Explain Plans PostgreSQL 9.0 - Part 2: JSON and JQuery Plan Viewer

nospam@example.com (Leo Hsu and Regina Obe) — Thu, 26 Aug 2010 04:13:00 -0400

In part 1 of this series on PostgreSQL 9.0 planner outputs, we demonstrated how to render explain plans in YAML, JSON, and XML using the new explain features in PostgreSQL 9.0. In this second part, we'll demonstrate how to build a user interface that allows you input a JSON formatted explain plan and have it render into a printable, navigateable display using JQuery, javascript and a little bit of HTML coding. In part 3 we'll do something similar using XML and XSLT programming.

For those who aren't familiar with JQuery, it is an MIT licensed javascript library that is fairly light weight and allows you to inspect and change html elements with fairly intuitive syntax, has some nice ajax methods and tools for converting xml/json to native objects that can be manipulated. You can check it out at JQUERY.

We are not experts in JQuery, but from what we have used of it, we really like it and the fact the base package is MIT licensed, fairly light weight and lots of plugins available for it are real pluses.

The most difficult thing I think most people find about reading explain plans is that they are upside down; it starts with a conclusion and backtracks how to arrive at it. Humans by nature think about planning steps from start to finish. In order to make an explain plan understandable to mere mortals, we generally display them upside down or having the child-nodes shown left most. We shall follow that approach.

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Loading and Processing GPX XML files using PostgreSQL

nospam@example.com (Leo Hsu and Regina Obe) — Wed, 29 Apr 2009 00:28:00 -0400

Simon Greener, wrote an article on how to load GPX xml files into Oracle XMLDB. That got me thinking that I haven't really explored all the XML features that PostgreSQL has to offer and to some extent I've been reticent about XML processed in any database for that matter.

In this article we shall attempt to perform the same feats that Simon did, but with PostgreSQL instead of Oracle XMLDB. Note while we are demonstrating this with a GPX file, the same XPath approach can be used to process any XML file.

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Fusion Charts and PostgreSQL Part 3: PHP Dashboard

nospam@example.com (Leo Hsu and Regina Obe) — Sat, 03 Jan 2009 15:19:00 -0500

In the first part of this series Fusion Charts and PostgreSQL Part 1: Database Analysis of USDA DB in our November/December 2008 issue, we did some back-seat analysis of a database we had never seen before and formulated some thoughts of things that would be useful to see in a dashboard as well as starting to develop some views to support our Dashboard. In the second part of our Fusion Charts series, we covered creating a Dashboard application in ASP.NET that demonstrated both VB.NET and C# variants using the database we loaded and prepped in Part 1.

In this part three of our series, we shall conclude by demonstrating the same application we did in ASP.NET in PHP.

We are going to create a simple dashboard that has the following features:

A drop-down list to allow the user to pick the kind of chart to display the data in (Bar, column, funnel etc)
A drop-down list that allows the user to pick the metric to explore -- e.g. Cholestrol, Vitamin K, Caffeine etc.
2 charts -- one chart showing the top 5 food groups for our metric and another showing the top 5 foods for our metric

Our final product will look like this:

You can see the app in action - USDA Food Stats and discover some interesting things about the food you eat or were considering eating.

Continue reading "Fusion Charts and PostgreSQL Part 3: PHP Dashboard"

Fusion Charts and PostgreSQL Part 2: ASP.NET Dashboard

nospam@example.com (Leo Hsu and Regina Obe) — Fri, 19 Dec 2008 17:19:00 -0500

In this part, we start the fun off by building an ASP.NET app in both VB and C#. In the next part of this series, we shall perform the same feat with PHP.

We are going to create a simple dashboard that has the following features:

A drop downlist to allow the user to pick the kind of chart to display the data in (Bar, column, funnel etc)
A drop downlist that allows the user to pick the metric to explore -- e.g. Cholestrol, Vitamin K, Caffeine etc.
2 charts -- one chart showing the top 5 food groups for our metric and another showing the top 5 foods for our metric

Our final product will look like this:

You can see the app in action - USDA Food Stats and discover some interesting things about the food you eat or were considering eating.

Continue reading "Fusion Charts and PostgreSQL Part 2: ASP.NET Dashboard"

Fusion Charts and PostgreSQL Part 1: Database Analysis of USDA DB

nospam@example.com (Leo Hsu and Regina Obe) — Tue, 16 Dec 2008 14:33:00 -0500

In our Product Showcase section of this issue, we introduced Fusion Charts which is a flash-based charting product that makes beautiful flash charts. It comes in both a free and a non-free more bells and whistles version.

In this 3-part series article we shall demonstrate using this with a PostgreSQL database, building a simple dashboard with ASP.NET and PHP. We shall demonstrate both C# and VB.NET both using the PostgreSQL NPGSQL driver.

For this first part we shall simply load the database, do a quick analysis of what we've got to report on and create some views to help us with our PHP and ASP.NET apps that will follow in parts 2 and 3.

We will be testing this on 8.3, but since the database is an old one, it should work just fine on older versions of PostgreSQL. We'll try to refrain from using new features of PostgreSQL.

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REST in PostgreSQL Part 3 B - The REST Client in Adobe Flex 3 with Paging

nospam@example.com (Leo Hsu and Regina Obe) — Mon, 19 May 2008 15:06:23 -0400

In prior articles of this series, we covered the following:

Showcasing REST in PostgreSQL - The PreQuel we went over what REST is and isn't
REST in PostgreSQL Part 1 - The DB components we loaded the Pagila database and created a db plpgsql search function to support our rest server service
REST in PostgreSQL Part 2 A - The REST Server service with ASP.NET we demonstrated a REST web service using Mono.NET, MS.NET both in C#, VB.Net/Monobasic
REST in PostgreSQL Part 2 B - The REST Server service with PHP 5 we demonstrated a REST web service using PHP 5
REST in PostgreSQL Part 3 A - Simple REST Client in Adobe Flex 3 we demonstrated a basic REST client in Adobe Flex

In this article we shall continue where we left off by adding paging functionality to our Adobe Flex REST grid client.

Continue reading "REST in PostgreSQL Part 3 B - The REST Client in Adobe Flex 3 with Paging"

REST in PostgreSQL Part 3 A - Simple REST Client in Adobe Flex 3

nospam@example.com (Leo Hsu and Regina Obe) — Wed, 07 May 2008 15:45:00 -0400

In prior articles of this series, we covered the following:

Showcasing REST in PostgreSQL - The PreQuel we went over what REST is and isn't
REST in PostgreSQL Part 1 - The DB components we loaded the Pagila database and created a db plpgsql search function to support our rest server service
REST in PostgreSQL Part 2 A - The REST Server service with ASP.NET we demonstrated a REST web service using Mono.NET, MS.NET both in C#, VB.Net/Monobasic
REST in PostgreSQL Part 2 B - The REST Server service with PHP 5 we demonstrated a REST web service using PHP 5

Continue reading "REST in PostgreSQL Part 3 A - Simple REST Client in Adobe Flex 3"

REST in PostgreSQL Part 2 B - The REST Server service with PHP 5

nospam@example.com (Leo Hsu and Regina Obe) — Wed, 09 Apr 2008 22:28:00 -0400

This is a continuation of our REST series. The following topics have already been covered

Showcasing REST in PostgreSQL - The PreQuel we went over what REST is and isn't
REST in PostgreSQL Part 1 - The DB components we loaded the Pagila database and created a db plpgsql search function that spits out XML to support our rest server service
REST in PostgreSQL Part 2 A - The REST Server service with ASP.NET we demonstrated a REST web service using Mono.NET, MS.NET both in C#, VB.Net/Monobasic

Now in this Part 2B series, we shall demonstrate the same REST server service using PHP

Setting up the PHP application

PHP already has the PostgreSQL drivers available as a .so (on Linux) or .dll on Windows. For windows users if you are running PHP under IIS and in ISAPI mode, you will not be able to dynamically load libraries, so you need to enable php_pgsql in your PHP.ini file.
We tend to keep it enabled regardless of which platform we are on since a lot of our PHP development involves PostgreSQL. The extension is php_pgsql in the php.ini file
PHP has numerous database abstraction libraries to choose from. We are using the adodb abstraction library for PHP which can be downloaded from http://adodb.sourceforge.net/.

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REST in PostgreSQL Part 2 A - The REST Server service with ASP.NET

nospam@example.com (Leo Hsu and Regina Obe) — Tue, 18 Mar 2008 22:33:00 -0400

Setting up the .NET application

Download the npgsql 1.01 driver from pgfoundary - http://pgfoundry.org/projects/npgsql. For ASP.NET 2.0 you'll want - Npgsql1.0.1-bin-ms2.0.zip and for Mono.NET you'll want Npgsql1.0.1-bin-mono-2.0.zip. Unzip and place the files in bin folder of your web app project.
Since we are just creating a simple REST web service and don't need any plumming of the standard SOAP like webservice, we will be using a .NET handler class (ashx) instead of an asmx. We have two versions listed below. One for C# and one for VB.NET/Mono Basic

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REST in PostgreSQL Part 1 - The DB components

nospam@example.com (Leo Hsu and Regina Obe) — Sun, 16 Mar 2008 18:33:00 -0400

In this section we'll go over creating the views and stored functions that our REST Server service will rely on.

Our REST service will be a thin wrapper around a pgsql function that accepts film queries and returns results in XML.

Loading the database

Step 1: Download the Pagila 0.10.0 database from http://pgfoundry.org/frs/?group_id=1000150&release_id=570 and load the Pagila database using the following commands:

Note:For windows users - psql is usually located at "C:\Program Files\PostgreSQL\8.3\bin\psql"


psql -h localhost -p 5433 -U postgres -c "CREATE DATABASE pagila ENCODING 'UTF8'"
psql -h localhost -p 5433 -U postgres -c "CREATE ROLE pagila_app LOGIN PASSWORD 'pg@123'"
psql -h localhost -p 5433 -U postgres -d pagila -f "pagila-schema.sql"
psql -h localhost -p 5433 -U postgres -d pagila -f "pagila-data.sql"

Continue reading "REST in PostgreSQL Part 1 - The DB components"