GeoServer and Teradata

Transcription

1 OpenGeo Version 1.0, July 2011 GeoServer and Teradata Your Geospatial Data Served on the Web Introduction What We ll Accomplish What is GeoServer? Installing GeoServer GeoServer Web Admin Interface Installing Teradata Extension Loading Teradata Spatial Data Viewing Teradata Data in GeoServer Setting a Spatial Index Viewing Teradata Data in GeoServer (Revisited) GeoServer Styling Styling and Best Practices Viewing with Other Visualization Tools More Information

2 Introduction Teradata s geospatial support has opened up many new possibilities for analyzing your enterprise data. Now, not only do have the ability to analyze the what of your data, you can now analyze the where as well. More info... For more information on GeoServer s capabilities with Teradata, please see the GeoServer documentation at: en/user/data/teradata.html With the increasing prevalence of GIS on the web, it makes perfect sense to be able to leverage both the power of the Teradata Database as well as web-based tools. To do this, we need to first understand the concept of the web geospatial stack. The web geospatial stack is the collection of utilities that provide everything necessary to serve data on the web. At its simplest, this consists of a spatial database, application server, and client. There are many tools that can fill each of these roles. This article will focus on GeoServer filling the role of application server, with Teradata providing the spatial database. A few different clients will be considered. GeoServer has recently added support for Teradata geospatial databases. Spatial databases are standard databases that have extra information added to make them spatially enabled. With GeoServer, Teradata spatial data can be easily served on the web. GeoServer also supports Query Banding, enabling request prioritization, logging, and debugging. In addition to reading and writing data in the database, GeoServer also increases the flexibility of the Teradata database through the use of SQL Views, or the creation of new layers directly in GeoServer based on SQL queries. With GeoServer SQL Views, spatial processing can be leveraged without the need for the creation of new views in the Teradata database itself. What We ll Accomplish In this article, we ll install GeoServer along with the Teradata extension, load spatial data into Teradata, add a spatial index to the data, connect GeoServer to this data, serve Teradata tables as map layers, style those layers, and view the results using various map clients. opengeo.org 2

3 What is GeoServer? GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards. More info... GeoServer: Since there s a lot to unpack in the above statement, let s take it in pieces: Application server: The application server is the software component that connects to a data source and serves that data in a way such that clients can read. GeoServer can be thought of like a web server, but for geospatial data. A web server connects to a data source, and serves it in such a way that browsers can read. With GeoServer, the source is a spatial database instead of HTML, and the client is a map application instead of a browser, but the principles are the same, Open source: GeoServer is a project developed by many organizations and individuals from around the world. Anyone is able to see and make modifications to the source code, and because of this, the product can improve and develop quickly. GeoServer development has been and continues to be funded by companies including Teradata to increase its utility and interoperability. Open standards: Continuing the analogy of the web server is helpful when discussing open standards. Every web browser uses HTTP to make connections with web servers. Imagine if each web browser used its own proprietary format! With this in mind, GeoServer uses published standard protocols when serving geospatial data. These protocols, such as Web Map Service (WMS) and Web Feature Service (WFS), are presided over by the Open Geospatial Consortium (OGC), a standards body. Because the protocols are published, any client can be created to take advantage of them, Protocols: Web Map Service (WMS) is a protocol for serving georeferenced map images. This is what most people think of when they think of web maps. These map images are constructed by combining the spatial data (raster, vector, or both) with visualization information (styling). Web Feature Service (WFS) is a protocol for serving the actual geospatial data itself. This enables the user/ client to request not only the images of the data, but the actual data itself. Using the above protocols, GeoServer abstracts the serving of data from the format of that data. Data can be in many forms, be it in a Teradata geospatial database, PostGIS database, Shapefile, or any number of other formats. In all cases, the output is always the standards of WMS and WFS. So clients only need to understand these protocols, and need not care about the underlying data format. That s the power of GeoServer! opengeo.org 3

4 Installing GeoServer First, let s install GeoServer. Here are the minimum system requirements for GeoServer: OS: Windows (XP and newer), Linux (any modern distribution), Mac (10.5 and newer) Memory: 512MB minimum dedicated to GeoServer (1GB recommended) The Teradata extension is only compatible with GeoServer and higher. More info... For considerations regarding GeoServer in a production environment, please see the following white paper: publications/geoserver-production/ Software: Java Runtime Environment (Oracle JRE 1.5 recommended), any servlet container Disk space: 100MB minimum (plus data) Display: A GUI is recommended for administration (800x600 or larger) We ll be using Windows in this article, although the steps for other operating systems are mostly the same. GeoServer comes packaged as a Web Archive (WAR) which can be used in any servlet container. The bundle we re using below contains the Jetty servlet container, but Apache Tomcat is often used in production environments. To download GeoServer: 1. Navigate to 2. Click on the Download link at the top, then click on Stable You will be directed to the most recent stable GeoServer version. There are multiple ways of installing GeoServer, but we ll use the OSindependent binary. Click that link to download the archive. Extract the contents of the archive to a newly created folder at C:\Program Files\GeoServer If you extracted correctly, you should see a few sub-directories inside this directory, such as bin, data_dir, webapps, etc. Now that we have the correct version of GeoServer, we can follow the instructions for running the Windows Binary as written in the GeoServer documentation: If you installed and launched GeoServer successfully, you should see the GeoServer Web Administration Interface (Web Admin) when you navigate to: opengeo.org 4

5 GeoServer Web Admin Interface GeoServer has a built-in web-based administration interface for easy configuration of most features of GeoServer, including services, layers, data sources, styles, and much more. As mentioned above, it is located at More info... To learn more about the configuration options available through this interface, see this page: user/webadmin/index.html Figure 1 GeoServer Web Administration Interface Installing Teradata Extension In order for us to connect to Teradata sources, we need to install the Teradata extension. We ll need one archive from GeoServer and one archive from Teradata. The instructions for installing the Teradata extension are located here: After installation, restart GeoServer. To verify that the extension was installed correctly: The Teradata extension for GeoServer has been tested on Teradata database 12, 13, and for both Windows and Linux. The instructions for installing the Teradata extension are located here: en/user/data/teradata.html Navigate back to the GeoServer Web Admin page at Log in as an administrator (using the login boxes at the top) using the username admin and password geoserver, then click Login. Figure 2 GeoServer Web Administration Interface once logged in 3. You should have many more options available to you now. Click the Stores link on the left side column. 4. Above the list of existing stores, click Add a new store. 5. You will be presented with a list of valid data sources. Teradata should be in the list, under Vector Data Sources. If you see Teradata, you ve installed everything successfully! opengeo.org 5

6 Figure 3 Teradata option under Vector Data Sources Loading Teradata Spatial Data Here we will load a shapefile into a Teradata database table using TDGeoImport, and then configure the database so that GeoServer can serve the data. We ll be assuming that your database has never been set up for geospatial. If you have been using geospatial, you may be able to skip some of these steps. You can get the TDGeoImport utility on the Teradata site: extensibility/teradata-geospatial You can get the TDGeoImport utility on the Teradata site: We will first create a user/database with the appropriate permissions to store spatial data. We ll call this user/ database geoserver with the password geoserver. CREATE USER geoserver AS PASSWORD = geoserver, perm = ; GRANT UDTUSAGE ON SYSUDTLIB TO geoserver; GRANT EXECUTE FUNCTION ON SYSSPATIAL TO geoserver; GRANT EXECUTE PROCEDURE ON SYSSPATIAL TO geoserver; GRANT SELECT ON SYSSPATIAL TO geoserver; GRANT ALL ON SYSSPATIAL.GEOMETRY_COLUMNS TO geoserver; GRANT ALL ON SYSSPATIAL.SPATIAL_REF_SYS TO geoserver; GRANT SELECT ON dbc.udtinfo TO geoserver; GRANT UDTUSAGE ON SYSUDTLIB TO geoserver; GRANT UDTTYPE ON SYSUDTLIB TO geoserver; You can use BTEQ, Teradata Administrator, or SQL Assistant to execute these SQL commands. With the permissions set, we are ready to load some data. We ll use the standard TDGeoImport utility to load a shapefile called states into our database. This file contains the geometries for the US states, plus some demographic information. Run the following command from the Command Prompt. This is a single command, wrapped over multiple lines for convenience: java -Xms256m -Xmx512m -classpath.; c:\program Files\Teradata\ Tdat\LTDBMS\bin\terajdbc4.jar ; c:\program Files\Teradata\Tdat\ LTDBMS\bin\tdgssjava.jar ; c:\program Files\Teradata\Tdat\LTDBMS\ bin\tdgssconfig.jar ;. com.teradata.geo.tdgeoimport -l / geoserver,geoserver -s geoserver -f states.shp -n STATES The above command assumes the following: The syntax for the TDGeoImport utility is described in the Teradata documentation entitled SQL Geospatial Types Document B A, available at The shapefile is called states and is in the current working directory The TDGeoImport utility is also in the current working directory The Teradata database is running on localhost ( ) opengeo.org 6

7 If your setup differs, you can alter the command accordingly. To verify that this import worked, run the following command: SELECT * from geoserver.states; You should see data corresponding to the US states. GeoServer allows for only a single connection to a Teradata database at a time, and will process requests serially. When multiple connections (e.g. multiple GeoServer instances) are opened to the same database, simultaneous writes may cause failures for one or more connections. For large datasets, the above command could return a large number of results. A safer, command to use for testing would be to return only the first 100 rows of the table: SELECT top 100 * FROM geoserver.states; The name of the database table is called STATES. GeoServer assumes upper case when working with Teradata data, so it is best to keep tables and databases in upper case to be consistent. We now have the spatial data loaded, but before we can view this data in GeoServer, we need to add an entry in the SYSSPATIAL.GEOMETRY_ COLUMNS table. This table will tell GeoServer, most importantly, the coordinate system (projection) of the data, along with the type of geometry contained and the bounds of the data. We happen to know that the data is stored in plain longitude/latitude format (EPSG:4326), but we need to figure out the internal Teradata SRID number that corresponds to this. Fortunately, that is easy to figure out with the following command: SELECT SRID FROM SYSSPATIAL.spatial_ref_sys WHERE AUTH_SRID=4326; The result in this case is This is the SRID that we will store in the GEOMETRY_COLUMNS table. Next we need to determine the bounds of the data. This can be accomplished via the Teradata MBR functions (note that the attribute column for the table is called GEOM): SELECT MIN(GEOM.ST_MBR_XMIN()), MIN(GEOM.ST_MBR_YMIN()), MAX(GEOM.ST_MBR_XMAX()), MAX(GEOM.ST_MBR_YMAX()) FROM geoserver.states; This returns the following values: , 24.96, , 49.37, which we will use in our statement to create the GEOMETRY_COLUMNS table. The AddGeometryColumn function automates the process of adding an entry to the GEOMETRY_COLUMNS table, while at the same time performing simple checks, such as the existence of the table and geospatial column. CALL SYSSPATIAL.AddGeometryColumn(, geoserver, STATES, geom, 1619, ST_Multipolygon, , 24.96, , 49.37, resultstring) ); The parameters in the above function are the catalog name (not applicable in this case), schema name, table name, geometry column name, SRID, geometry type, the layer bounds, and the result string. opengeo.org 7

8 Viewing Teradata Data in GeoServer Now that we have our spatial data loaded (though not optimized), we can connect to GeoServer. 1. Navigate to 2. Log in as above (using credentials admin / geoserver) if you aren t already logged in. 3. Click the Stores link on the left side. 4. Above the list of existing stores, click Add a new store. The traditional way to use database-backed data is to configure either a table or a database view as a new layer as described here. With GeoServer one also has the ability to create a new layer by specifying a raw SQL query without the need to actually create a view in the database. The SQL can also be parametrized, and parameter values passed in along with a WMS or WFS request. For more information on SQL views in GeoServer: stable/en/user/data/sqlview.html Figure 4 New Vector Data Source from Terdata Database You will be presented with a list of valid data sources. You should see Teradata in the list, under Vector Data Sources. Click that link. (Don t click the link that says Teradata (JNDI) ; that s a different way of connecting that isn t important now.) Fill out the form with the following information (leaving everything else as the default): Data Source Name: Teradata Host: Database: geoserver User: geoserver Password: geoserver For details on the fields, please see this page: stable/en/user/data/teradata.html 7. When finished, click Submit. 8. You will see a list of all the spatially enabled database tables in this database. If the STATES table isn t here, return to the steps above on spatially enabling a database table and verify that those steps were accomplished properly. Figure 5 Adding the STATES layer from the Teradata store 9. Next to the table called STATES, click the Publish button. 10. You will be taken to the configuration page for new layers. This is where you can specify information about the layer such as bounding box, projection, and style. We don t need to do much here for now. opengeo.org 8

9 11. Find the Declared SRS field. It should display EPSG:4326. If not, review the steps above on populating the GEOMETRY_COLUMNS table. 12. In the Bounding Boxes section, click on Compute from data and then Compute from native bounds. Both sets of dialog boxes should populate with values matching to the bounds of the layer as determined above. Figure 6 Verify SRS and Bounding Boxes 13. When finished, click Save. Your layer is now being served with GeoServer, so let s view it. GeoServer comes bundled with an included OpenLayers client, a browserbased mapping client, in order to make previewing layers easy On the left side on the window, click on Layer Preview. In the list of layers, you should see a row for cite:states. On that row, click on the link that says OpenLayers. A new browser tab will open with an OpenLayers client. Inside that map window will be your layer. Click and drag the mouse to explore the layer. Congrats! Figure 7 Preview in OpenLayers opengeo.org 9

10 Setting a Spatial Index Tessellation Table We have loaded data, but haven t done anything about a spatial index. A spatial index is vital for most spatial data sets because it optimizes retrieval of features and therefore decreases the query time. A query that needs to look through a table with 50 rows may not take very long, but if that table has 50,000,000 rows, clearly that will not do. Teradata uses an spatial index structure called tessellation in order to optimize spatial queries. In order to process a spatial index properly, we will need to create a tessellation table in the SYSSPATIAL database, the database responsible for holding all spatial functions, and then create an index table for our data set. For more information on tessellation, please see the following references: SQL Geospatial Types Document B A, available at Orange Book: Teradata Spatial Features User s Guide, Teradata Orange Book B01, available when you register through Your Service from the Support Services link at The following SQL query will create the tessellation table: CREATE SET TABLE SYSSPATIAL.tessellation, NO FALLBACK, NO BEFORE JOURNAL, NO AFTER JOURNAL, CHECKSUM = DEFAULT ( F_TABLE_SCHEMA VARCHAR(128) CHARACTER SET UNICODE NOT CASESPECIFIC NOT NULL, F_TABLE_NAME VARCHAR(128) CHARACTER SET UNICODE NOT CASESPECIFIC NOT NULL, F_GEOMETRY_COLUMN VARCHAR(128) CHARACTER SET UNICODE NOT CASESPECIFIC NOT NULL, U_XMIN FLOAT, U_YMIN FLOAT, U_XMAX FLOAT, U_YMAX FLOAT, G_NX INTEGER, G_NY INTEGER, LEVELS INTEGER, SCALE FLOAT, SHIFT INTEGER ) UNIQUE PRIMARY INDEX ( F_TABLE_SCHEMA, F_TABLE_NAME, F_GEOMETRY_COLUMN ); We also want to grant our user access to this table: GRANT ALL ON SYSSPATIAL.TESSELLATION TO geoserver; Let s now populate the tessellation table, and for this we need to determine the tessellation universe. The Teradata tparms utility will output recommended tessellation parameters. The Geospatial Orange Book has more details on using the tparms utility. There is no one way to determining the tessellation universe, as it is dependent on the current and future bounds of the data set, but there are generally three ways to set the tessellation universe If the data is static, use a constrained bounds that is just slightly larger than the layer bounds. If the data is dynamic, use a large bounds so as to encompass the expected future geometries. If unsure, use the world bounds, or the max extent for the projection. Regardless of which method you choose, the tessellation table must always be larger than the bounds of the data. A good rule of thumb would be to set the tessellation universe to at least 50% greater of the initial data set minimum bounding rectangle if possible, then set the tessellation grid so as to fit about 100 features into one tile or so. If the data is sparse (features concentrated in a small area, with lots of empty opengeo.org 10

11 space) then the number of tiles should be larger and the grid denser. In this example, for simplicity, we are going to use the world bounds, which for our coordinate system is -180, -90, 180, 90. We also need to determine the maximum number of grid entries, the number of levels in the grid, the scale factor, and the shift, if any. For such a small dataset, we can get by with 10x10 grids with one grid level, a scale factor of 0.1 and a zero shift. (In any real-world data set, this would be far too small, but it is an easily understandable example of tessellation.) We will populate all of this information into the tessellation table, incorporating our tessellation universe bounds as determined above. INSERT INTO SYSSPATIAL.tessellation VALUES ( geoserver, STATES, GEOM, -180, -90, 180, 90, 10, 10, 1, 0.1, 0 ); The tessellation table divides the world into a grid for easier sorting of features. Each grid entry will have its own id number. Figure 8 A sample tesselation grid. Index Table Now that the tessellation table is taken care of, we move on to the index table. By custom, the spatial index table is named: [TABLE_NAME]_[GEOMETRY_COLUMN]_idx The table name is case sensitive. The case of the table name and geometry column must match the case here. In our case, the table name will be called STATES_GEOM_idx. This table will have two columns, the primary key for the table and the tessellation cell ID (cellid) pointing to the specific cell in the grid where that feature is contained. Unfortunately, the TDGeoImport utility only creates a table with a primary index, not a primary key, so we ll need to create one manually. In our data set, the column STATE_ABBR contains a unique value (the state two letter abbreviation). But since it was created without the NOT NULL constraint (required for primary keys), let s just copy the column contents to a new column, called ID, which will be our table s primary key. opengeo.org 11

12 The following commands will accomplish this: ALTER TABLE geoserver.states ADD ID VARCHAR(254); UPDATE geoserver.states SET ID=STATE_ABBR; ALTER TABLE STATES ADD ID NOT NULL; ALTER TABLE STATES ADD PRIMARY KEY (ID); Now with a primary key on our original table, we can create our index table: CREATE TABLE geoserver.states_geom_idx (ID VARCHAR(254), cellid INTEGER); We will populate this table with the primary key values, plus the output of the tessellate_index() function, which returns the cell ID for the given geometry. INSERT INTO geoserver.states_geom_idx SELECT ID, SYSSPATIAL.tessellate_index( GEOM.ST_MBR_XMIN(), GEOM.ST_MBR_YMIN(), GEOM.ST_MBR_XMAX(), GEOM.ST_MBR_YMAX(), -180, -90, 180, 90, 10, 10, 1, 0.1, 0 ) FROM geoserver.states; To verify that this index was created properly, run the following command: SELECT * FROM geoserver.states_geom_idx; You should see a the primary key in the first column and the cell ID in the second column. A little bit of sleuthing will shed some light on this table. One would expect that features corresponding to states that are very close together would be in the same cell (and thus have the same cell ID). Take Maryland (MD) and Virginia (VA), for example. They both have a cellid of 1153, which makes sense as they are adjacent. However, Oregon, all the way across the county has a cellid if Given the various geographic proximities, the different cellid values make sense. For large datasets, the above command could return a large number of results. A safer, command to use for testing would be to return only the first 100 rows of the table: SELECT top 100 * FROM geoserver.states_geom_idx; We now have created a proper spatial index on our data set. opengeo.org 12

13 Triggers A spatial index is the gatekeeper for queries, sheltering the spatial table that contains the much more cumbersome geometries. So what if the underlying spatial table changes? Without any notification, the spatial index wouldn t know about any new (or changed) features, and thus would yield incorrect results. To fix this, we introduce triggers. When a feature is inserted, updated, or deleted, a corresponding trigger will be run which will update the index table accordingly. INSERT trigger: CREATE TRIGGER geoserver.states_geom_ mi AFTER INSERT ON geoserver.states REFERENCING NEW TABLE AS nt FOR EACH STATEMENT BEGIN ATOMIC ( INSERT INTO geoserver.states_geom_ idx (ID, cellid) SELECT ID, sysspatial.tessellate_index( GEOM.ST_MBR_XMIN(), GEOM.ST_MBR_YMIN(), GEOM.ST_MBR_XMAX(), GEOM.ST_MBR_YMAX(), -180, -90, 180, 90, 10, 10, 1, 0.1, 0 ) FROM nt WHERE GEOM IS NOT NULL; ) END UPDATE trigger: CREATE TRIGGER geoserver.states_geom_ mu AFTER INSERT ON geoserver.states REFERENCING NEW TABLE AS nt FOR EACH STATEMENT BEGIN ATOMIC ( DELETE FROM geoserver.states_geom_idx WHERE ID IN (SELECT ID FROM nt); INSERT INTO geoserver.states_geom_ idx (ID, cellid) SELECT ID, sysspatial.tessellate_index( GEOM.ST_MBR_XMIN(), GEOM.ST_MBR_YMIN(), GEOM.ST_MBR_XMAX(), GEOM.ST_MBR_YMAX(), -180, -90, 180, 90, 10, 10, 1, 0.1, 0 ) FROM nt WHERE GEOM IS NOT NULL; ) END DELETE trigger: CREATE TRIGGER geoserver.states_geom_ md AFTER DELETE ON geoserver.states REFERENCING OLD TABLE AS ot FOR EACH STATEMENT BEGIN ATOMIC ( DELETE FROM geoserver.states_geom_idx WHERE ID IN (SELECT ID FROM ot); ) END opengeo.org 13

14 Viewing Teradata Data in GeoServer (Revisited) We want to ensure that GeoServer is using the spatial index that we set up Clear the resource cache by clicking on Server Status, scrolling down to Resource Cache, and clicking the Clear button Click on the Layer Preview menu. Find the row that contains your layer and click on OpenLayers. The layer will be displayed, this time leveraging the spatial index. We shouldn t detect any performance increase here for such a small dataset. For small datasets, a spatial index doesn t make much sense, and in fact can create a processing overhead. But for any cases larger than a simple test case like our own, a spatial index will be beneficial and even vital to displaying spatial data with optimal performance. GeoServer Styling Geospatial data has no intrinsic visualization. Points, lines, and polygons don t look like anything until we assign it that look. So, a primary component of any map image aside from the data itself is styling. GeoServer uses a markup language called Styled Layer Descriptor (SLD), an XML-based markup language from expressing how to render geospatial data. It contains most common visualization directives, such as color, shape, size, stroke, fill, opacity, and much more. This information is stored in GeoServer as a named style, which is associated with a layer. So when the WMS request in the previous section was made, the layer data was styled according to the style associated with that layer. We kept the style as the default for the layer, which is why the features all had a flat gray look. But that is easy to change. Let s change the features from gray to blue to get a sense of how the styling works. 1. Navigate back to localhost:8080/geoserver/ For more information about SLD, please see the Styling section in the GeoServer Documentation at org/latest/en/user/styling/index.html Figure 8 Editing an SLD through GeoServer. 2. Click on the Styles link. 3. Click Add a New Style. 4. Name the new style bluepoly We re going to create a new style, but copy from the existing one that our states layer is using. In the box titled Copy From Existing Style, select polygon, then click Copy... Now let s take a look at the style information. the line that says <CssParameter name= fill >#AAAAAA</ CssParameter> 7. Change the color from #AAAAAA to #0000CC. The latter is the RGB color code for a muted blue. opengeo.org 14

15 8. We want to make sure that we didn t make a typo, so click Validate. If you see an error, check your work. 9. When finished, click Submit. 10. We made a copy of the existing style, but now we need to associate our layer with this new style. Click on Layers (not Layer Preview). Figure 9 Setting the default style to bluepoly. 11. Click on the cite:states layer. 12. This page should look familiar, as this is the layer configuration page we saw earlier. This time, we re going to edit the style information for this layer. Click on the Publishing tab at the top of the page. 13. Find the box titled Default style (not the list of Available Styles). Find the style named bluepoly that we just created and select it. The preview box will change from a gray square to a blue square. 14. When finished, click Save. 15. Now let s reload our OpenLayers preview. If you closed the tab containing the OpenLayers preview, follow the steps in previous sections to open it again. If we did all the steps correctly, our layer should have changed color. Figure 10 Previewing in OpenLayers. opengeo.org 15

16 Styling Best Practices There is more to styling than just color or shape. Styling performs a functional, optimization role as well, because it is possible to adjust styling based on attributes and also zoom levels. This has important ramifications for performance. It is important to consider how much data you serve. A map that contains 200,000 points isn t going to be useful (at least not humans), since people can t process that much information at once. A good rule of thumb is that any map that contains more than 1,000 pieces of information is too crowded. Styling in GeoServer allows for a great opportunity for reducing the amount of data served in your maps. The two best ways to accomplish this is to limit map display by attribute and by zoom level. The way that both of these are done is with the use of SLD filters. A filter directs a styling rule to take effect only if a given condition is true. For example, say a data set had an attribute called roadclass. You could create a rule that stated to display the geometries only when the value of the attribute roadclass is highway. In this way, you could have a very large data set, while at the same time, not be forced to render it all at once. Styling by zoom level works in the exact same way. Taking the example of a road layer again, you wouldn t want to display all the small, back roads when looking at a national map! In this case, you would set up a filter such that the local roads would display only when the map scale is below a certain value (zoomed in). All of those local roads won t display otherwise. A combination of filtering by attribute and by zoom level will enable you to ensure that your map layers are always showing just the proper amount of data. Of course, splitting out your data into individual tables and then simplifying the style is slightly more efficient from a rendering perspective, but the options are there. It is also possible to associate different styles with the same map layer, so that different requests can output differently over the same layer. One final note about best practices with attribute-based styles. Because GeoServer will query the database and iterate over all geometries to figure out which geometries have the desired attribute value, it is highly recommended to put an index on that specific attribute. Viewing with Other Visualization Tools We have already seen how to view GeoServer WMS output with GeoServer s built-in OpenLayers client and straight in the browser. But there are many other way to view GeoServer layers. The following is just a sample. Raw WMS When GeoServer serves a layer, it by default serves the layer using WMS. This means that a standard WMS call to GeoServer will return an image. OpenLayers is set up to make standard WMS calls, and insert the images retrieved into a dynamic browser-based map window. While convenient, OpenLayers isn t the only way to retrieve a WMS image. For example, GeoServer also has a built in WMS renderer called the WMS Reflector, that will output an image with a short URL request: opengeo.org 16

17 This is a shortened version of the much longer, but equivalent: n=1.1.0&request=getmap&layers=topp:states&styles=&bbox= , , , &width=512&height=216&srs=epsg:4326&format=image/png While the full details of how WMS works are beyond the scope of this document, a quick look at this request shows that it is comprised of various parameters (layer name, size, style, etc), which is interpreted by the WMS and determines the output. Google Earth Google Earth is a very popular 3D map rendering tool. GeoServer has native support for serving data in Google Earth because of its KML output format. KML is the markup language that Google Earth uses to render data. GeoServer can either export a static KML file which can be loaded into Google Earth, or can be directly connected to Google Earth via a Network Link for a dynamic map. To connect to GeoServer via a Network Link, please see the GeoServer documentation: user/googleearth/ quickstart. html#adding-a-network-link Google Earth can be downloaded for free at The simplest way to see GeoServer data in Google Earth is via a static KML output. This can be accomplished in much the same way as for OpenLayers. 1. Navigate back to 2. Click on Layer Preview. 3. Find our layer cite:states again. Click on the link in that row that says KML. 4. GeoServer will output a KML file. If you have Google Earth installed on your machine and associated with KML files, your computer will ask to open Google Earth. Click OK. 5. Google Earth will display your data. Notice that the styles that we worked with in the previous section are displayed here as well. Just like in OpenLayers, clicking on a feature will bring up a popup that contains a listing of that feature s attributes. Figure 11 Viewing in Google Earth opengeo.org 17

18 udig udig, or User-friendly Desktop Internet GIS, is an open-source desktop GIS tool. It is freely available at udig can connect to WMS and WFS sources, and therefore can view data served from GeoServer. Let s connect to GeoServer s WMS. 1. Load udig. 2. Go to the Layer menu and select Add... udig can also connect directly to Teradata without using the GeoServer WMS as an intermediary. For information of connecting udig to Teradata, please see the udig documentation: display/en/teradata+page 3. Select Web Map Server in the dialog box In the box, that follows, enter the URL that points to the GeoServer WMS, which is: In the next dialog, you ll see a list of the layers served through GeoServer. Place a check mark next to the layer you want to load (you can use the perennial cite:states, or pick another) and then click OK. You should now see the layer in the map window, using the styling as known to GeoServer. Figure 12 Viewing in udig GeoServer WFS As discussed earlier, GeoServer also serves data in the Web Feature Service protocol. This protocol serves the actual geographic features, not map images, and thus can be thought of as the source code to the map itself. Mapping clients can connect to the GeoServer WFS to do client side rendering. Let s start by seeing how a WFS request output looks. In your browser, navigate to the following URL: request=getfeature&typename=cite:states&maxfeatures=1 This request will output the GML code for a single geometry in the data layer. (Which geometry is dependent on the data source.) If you were to remove the maxfeatures parameter, the browser would display the entire data table! While that wouldn t be helpful, it could be useful to export data served in GeoServer to another format. GeoServer has a shapefile output option to easily export opengeo.org 18

19 whole or partial data layers as a shapefile. So here is a slightly-edited request: est=getfeature&typename=cite:states&outputformat=shape-zip This request collects all of the geometries into a zipped shapefile, which a browser would then download. This output is dynamic, which is to say that the contents of the output are current data set as known to GeoServer. Since this layer is backed by a database table, and databases are not static entities, this endpoint allows for a dynamic output of data in a common and portable format. In effect GeoServer here is acting as a Teradata to shapefile exporter, a nice full circle from where we began. More Information In this article, we have merely scratched the surface of what is possible with GeoServer and Teradata s geospatial capabilities. For more information, please see the following resources:: GeoServer GeoServer Documentation Teradata Geospatial Orange Book: Teradata Spatial Features User s Guide, Teradata Orange Book B01, available when you register through Your Service from the Support Services link at Teradata Geospatial Types SQL Geospatial Types Document B A available at opengeo.org 19

20 Summary Teradata s geospatial support has opened up many new possibilities for analyzing your enterprise data. Now, not only do you have the ability to analyze the what of your data, you can now analyze the where as well. GeoServer has recently added support for Teradata geospatial databases. With GeoServer, Teradata spatial data can be easily served on the web. This article will show how to load spatial data into a Teradata database and serve it on the web using GeoServer. Discussion will also include spatial indexing, map styling, and viewing using a variety of map clients. Risk-Free Evaluation It s free and easy to gain access to complete OpenGeo platforms on a supported (Basic Level) evaluation basis. Go to for a free 30-day trial. For more information on upgrading your service to enterprise-class reliability and maintainability with the OpenGeo Suite, contact your OpenGeo representative. 148 Lafayette Street, Penthouse New York, NY Phone: OPENGEO inquiry@opengeo.org About Us OpenGeo is a social enterprise working to build the best web-based geospatial technology. Our company brings the best practices of open source software to geospatial organizations around the world by providing enterprises with supported, tested, and integrated open source solutions to build the Geospatial Web. OpenGeo also supports open source communities by employing key developers of PostGIS, GeoServer, OpenLayers, GeoWebCache and GeoExt. The company has a seven year history of providing successful consulting services and products to clients like Google, the World Bank, Portland Tri- Met, and the Open Geospatial Consortium. OpenGeo is the geospatial division of OpenPlans, a New York-based 501(c)(3) non-profit, which informs and engages communities through journalism and open source software. opengeo.org 20