March 2008 Oracle Spatial User Conference · JSON response PL/SQL Process ... An AJAX request to...

March 2008

Oracle Spatial User Conference


March 13, 2008

Sheraton Seattle Hotel

Seattle, Washington USA

Trevor QuinnPrincipal DeveloperSystalex Corporation

March 2008


Web Mapping with Virtual Earth and Oracle in EPA's Grant Tracking Systems

March 2008


• GRTS: EPA's Grant Reporting and Tracking System for EPA's Non-Point Source Reduction Grants• Enterprise web application• Tracks grant activities, budgeting, performance,

and results. Not a GIS application per se.• Mapping streamlines user interface, allows users to

more easily find grants, summarize program data, and enter locational information about grants

• Microsoft Virtual Earth is now an agency approved geospatial technology

Project BackgroundMarch 2008


Technologies Used

• Microsoft Virtual Earth SDK 6• JavaScript/AJAX: Prototype 1.6 and

Scriptaculous• Oracle 10g Locator• Oracle Application Express 3.0• Oracle MapViewer (WMS) ‏• PL/SQL (feature processing) ‏• Java 1.4 (WMS tile server) ‏

March 2008


Overview

• Concepts and Implementation• Tiles: Deploying a custom tile server for Virtual

Earth (or Google Maps) ‏• Reflecting WMS as Virtual Earth tiles• Caching tiles

• Features: Passing data between Virtual Earth and Oracle 10g

• Enabling AJAX calls in Oracle Application Express• Generating and parsing GeoJSON for Virtual Earth• Submitting features to the database as WKT

• Demonstration

March 2008


Data Flow OverviewMarch 2008


WMS Virtual Earth Tile Cache

Web browser

Oracle 10g

APEX 3.0

JDBCImage files

Image files

Features (GeoJSON and WKT)‏

TilesDeploying a custom tile server

March 2008


Tiles

• VE tiles are 256px-by-256px quadtree-indexed image files that together form a grid of a map in Google's Mercator-projected geographic coordinate system

• Any map that matches or approximates this projection can be broken up into usable tiles (including WMS) ‏

March 2008


TilesMarch 2008


Image reproduced from Microsoft MSDN website

Sample VE Tiles and Their Quad CodesMarch 2008


0320

0212300

02310103012123

Reflecting WMS as Tile Images

• We need a process for converting a VE tile request into a WMS request and returning the result

• This process must be callable through a URL, passed to Virtual Earth's JavaScript API

• Once provided the URL, the VE API will overlay WMS tiles on the VE background at a matching scale (with user-specified transparency) ‏

March 2008


Overlaying WMS Tiles on Virtual EarthMarch 2008


Virtual Earth

WMS

Combined

Tile Serving Process (without Caching)‏March 2008


WMS VE Tile Cache BrowserOracle

10g

Tile request(HTTP Get)‏

WMS request(HTTP Get)‏JDBC

queries

JDBC result sets

PNG fileresponse (HTTP) ‏

Forwarded PNG fileresponse (HTTP) ‏

Reflecting WMS as Tile ImagesMarch 2008


AddTileLayer: function(mapName, opacity)‏{ var tileSourceSpec = new VETileSourceSpecification(mapName, "http://aruba.systalex.com/WMSTileServer/?MAP_NAME=" + mapName + "&VE_QUAD_CODE=%4"); tileSourceSpec.NumServers = 1; tileSourceSpec.Opacity= opacity; this.map.AddTileLayer(tileSourceSpec, false); },

VE replaces with a quadtree tile code based on scale and extent of current map view(023, 121122, 13, etc.)‏

VE Tile Cache ServletMarch 2008


public Box QuadKeyToBox(String quadString, int x, int y, int zoomLevel) { char c = quadString.charAt(0); int tileSize = 2 << (18 - zoomLevel - 1); if (c == '0') { y = y - tileSize; } else if (c == '1') { y = y - tileSize; x = x + tileSize; } else if (c == '3') { x = x + tileSize; } if (quadString.length() > 1) { return QuadKeyToBox(quadString.substring(1), x, y, zoomLevel + 1); } else{ return new Box(x, y, tileSize, tileSize); }}// Then convert Box x and y values to WGS84 latitude and longitude

VE Tile Cache Java servlet (adapted from Active Web Solutions C# source)‏

Tile Serving Process (with Caching)‏March 2008


WMS VE Tile Cache BrowserOracle

10g

Tile request(HTTP Get)‏

Forwarded PNG fileresponse (HTTP) ‏

(Tile in local cache) ‏

Caching Tiles in the VE Tile Cache ServletMarch 2008


public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ... File f = new File(dir, quadKey + ".png"); if (!f.exists()) { // If the image is not already cached, make call to WMS BufferedImage bi = ImageIO.read(buildURL(ml, quadKey)); ImageIO.write(bi, "png", response.getOutputStream()); f.createNewFile(); // Write the image to the designated tile cache folder on the server ImageIO.write(bi, "png", f); } else { // Otherwise, just display the image from cache ImageIO.write(ImageIO.read(f), "png", response.getOutputStream()); } }

Servlet HTTP response source code fragment:

FeaturesPassing data between Virtual

Earth and Oracle 10g

March 2008


Adding Features to the WMS Overlay in Virtual EarthMarch 2008


Feature Serving ProcessMarch 2008


Browser

AJAX feature request (HTTP Get)‏

JSON response(HTTP)‏PL/SQL Process

in Oracle 10gHTTP Server

AJAX feature request

JSON response(HTTP)‏

Serving Features to Virtual EarthMarch 2008


/** * Makes an AJAX request to the database for a feature corresponding to a * drainage area ID. * * @param {Object} drainageAreaId * @return {Object} drainageArea */function LoadDrainageArea(drainageAreaId)‏{ var ajaxRequest = new htmldb_Get(null, $('pFlowId').value,'APPLICATION_PROCESS=LoadDrainageArea',0); ajaxRequest.add('P1131_PRJDRAR_SEQ',drainageAreaId); drainageArea = ajaxRequest.get(); ajaxRequest = null; return drainageArea;}

An AJAX request to run an APEX PL/SQL process:



DECLARECURSOR map_cur IS SELECT * FROM drain_area_map m WHERE m.id = :P1131_ID;htp.prn('{');htp.prn(' "type": "FeatureCollection",');htp.prn(' "features": [');BEGIN FOR v_map IN map_cur LOOP htp.prn(' {'); htp.prn(' "type": "Feature",'); htp.prn(' "id": "' || v_map.prjdrarmap_seq || '",'); htp.prn(' "geometry": {'); htp.prn(' "type": "MultiPoint",'); htp.prn(' "coordinates": [ [' || v_map.geo_start.sdo_point.x || ', ' || v_map.geo_start.sdo_point.y || '],' || ' [' || v_map.geo_end.sdo_point.x || ', ' || v_map.geo_end.sdo_point.y || '] ]'); htp.prn(' "properties": {'); ... htp.prn(' }'); htp.prn(' }'); END LOOP;END;

The APEX PL/SQL process that queries for and returns features:



{ "type": "FeatureCollection", "features": [ { "type": "Feature", "id": "112322", "geometry": { "type": "MultiPoint", "coordinates": [ [102.0, 0.0], [103.0, 1.0] ] }, "properties": { "Stream name": "Miller Creek", "Inserted by": "John Wilson" "Inserted date": "03-MAR-2007" } }, ... ]}

The JSON representation of features:



function GeoJSONCollection2VEShape(geoJSONCollection) { for (var i = 0; i < geoJSONCollection.features.length; i++) { feature = geoJSONCollection.features[i]; switch (feature.geometry.type) { case "MultiPoint": for (var j = 0; j < feature.geometry.coordinates.length; j++) { coordinate = feature.geometry.coordinates[j]; latLong = new VELatLong(coordinate[1], coordinate[0]); var shape = new VEShape(VEShapeType.Pushpin, latLong); shape.SetDescription(Object.toJSON(feature.properties)); veShapeArray.push(shape); } break; this.GetVEShapeArray = function() { return veShapeArray; }}...var converter = new GeoJSONCollection2VEShape(geoJSONFeatureCollection); var veShapeArray = converter.GetVEShapeArray();VEShapeLayer.addShape(veShapeArray[0]);

Parsing JSON and displaying in Virtual Earth

Submitting Features to the Database from Virtual EarthMarch 2008


• A similar process is used for submitting features to the database from Virtual Earth (create AJAX call on client, create PL/SQL process in database)‏

• When creating features for database submission, forming WKT is easier than JSON, because Oracle Spatial has:

SDO_UTIL.FROM_WKTGEOMETRY( geometry IN CLOB) RETURN SDO_GEOMETRY;

D E M O N S T R A T I O N

Web Mapping with Virtual Earth and Oracle 10g in EPA's Grant Tracking

Systems

Resources

• MSDN Building Your Own Tile Server: http://msdn2.microsoft.com/en-us/library/bb545006.aspx

• Accessing WMS from Virtual Earth by Rob Blackwell of Active Web Solutions Ltd. http://viavirtualearth.com/vve/Articles/WMS.ashx

• Video demonstration of the Virtual Earth in the EPA grant tracking application:http://www.systalex.com/capabilities/web_dev.html

March 2008


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