STRATEGY FOR DATA MANAGEMENT FOR GIS BASED LOCAL
SEARCH PORTAL WITH REFERENCE TO PRIMARY SOURCE DATA
Vivek Kumar Purwar1, Pawan Kumar2, Dr. Abhay Kumar(Guide), Mr. Ritesh Ambastha(Co-Guide) School of Electronics, Devi Ahilya Vishwavidalaya, Indore
1 Corresponding Author, 2
Co-Author, Email id: [email protected], [email protected]
ABSTRACT
The Indian internet landscape is getting more competitive day by day. Search engines have traditionally been at the heart of how the internet works, and we now have GIS integrated with Search Engines, so that not only we find the Search results but we can see their positions on Map along with all other relevant details.
According to a study conducted by the Internet and Mobile Association of India (IAMAI), about 65 million people use search engines, with every user spending on an average 20 hours a week browsing the net for data and information, including news. The current market size for search engine advertising is pegged at $50 million (Rs.2.3 billion) annually.
With an Internet user base of 40 million and growing at about 50 percent annually, the potential for search engine usage is enormous. Moreover Awareness of mobile local search continues to grow with consumers, creating new opportunities for brands and vendors to exploit the power of the mobile channel. Both GIS and Local Search involve several high end technologies and various factors need to be planned and considered to implement these kinds of projects successfully. The main difficulty is in lack of reliable GIS data due to volatile infrastructure and lack of fine grained deterministic data. Also non availability of properly trained GIS people and technical resources to carry on the detailed aspects of project smoothly lessen the speed of the project in a big way.
In this GIS based local search project, I have tried to understand the technologies involved, how they are integrated with each other, what are the difficulties these types of projects go through during planning and development stage, how Data collection and efficient data management can be done which is the base of these kind of projects and what are the improvement areas for a successful implementation. This case study gives us the idea about the base preparation to build a local Search Portal. This thesis broadens knowledge base about all the aspects of the project which was indeed case study to be a part of these types of projects in future.
I
INTRODUCTION
Geographical Information Systems have evolved from Desktop Environments to Enterprise – wide deployment and today we are on the cusp of a world where GIS applications are entrenched in mainstream IT applications & Mobile GIS enriches the average consumer’s life.
The collaboration ofGIS with information technology is revolutionary and challenging to understanding and implementing. We have to understand the compatibility between various technology used in portal where search engine integrates with GIS data.
In this case study we try to understand what technologies should be used and how compatibility could be maintain. Such type of portals have two main challenges, these are displaying routable routes and displaying map in the web portal.
To exploit the scope to work on different Strategies and Methodologies pertaining to Primary & other Data Collection, Editing, Filtration, Quality check & how data is stored in Database, Database Management for both Spatial & Non-spatial data & Data Retrieval
GIS applications consist of accurate maps, corresponding databases and the software that processes user requests and renders information in a useful manner in a web. There are several sectors where GIS Application is playing a vital role, like – Transportation & Logistics, Utilities, Healthcare, Manufacturing & More precisely Local Search for Business Entities and Telecom Industries.
To get hands on expertise to experiment with different software tools & GPS that how those are being used in Data Collection, Editing & Quality Control processes.
GIS will cause profound changes in the way we collect, store, analyze and share geographical data. Many changes are predictable, and their impact can be estimated before they come to pass. With the passage of time and the coming up of the latest technologies, GIS’ shackles are being broken.
Yet the biggest constraint in any GIS application remains the availability of Spatial Data. In India, most organizations who have adopted GIS are still spending a lot of time and money on building data.
The first reason for this is the disparity between various systems from which data has to move from one form to another before the desired output becomes available. The second reason is very tight government control on spatial data acquisition, and the high cost of satellite and aerial data.
Another major constraint for GIS is awareness levels which is relatively low in India. However thanks to extensive research & education, many Government, semi-government and a few Corporate have started realizing the immense potential of a successful GIS implementation off late & so it seems that the day is not far when both GIS applications & technologies will be more easier & less time consuming to implement. To exploit the scope to work on different Strategies and Methodologies pertaining to Primary & other Data Collection, Editing, Filtration, Quality check & how data is stored in Database, Database Management for both Spatial & Non spatial data & Data Retrieval.
To get hands on expertise to experiment with different software tools & GPS that how those are being used in Data Collection, Editing & Quality Control processes.
II
Functionalities
A Web mapping Platform that power many map-based services like:
Search: Local search to find businesses & POI’s (Point of Interests) on the map along with their addresses, contact numbers, Photos and links to other detailed information.
Building Search: Search Buildings along with their addresses, contact nos. at a particular zoom level. Routing: Get Route Directions on the map, calculate shortest path and Print
Directions.
Figure 1(Methodology regarding Data Collection, Tools Used, Editing & Quality Check)
A
Data Collection
“Data refers to the of natural phenomena descriptors, including the results of experience, observation or experiment, or a set of premises. This may consist of numbers, words, or images, particularly as measurements or observations of a set of variables”.
In this case study Raw Data mainly comes from GPS Survey. Raw data is a relative term; data processing commonly occurs by stages, and the "processed data" from one stage may be considered the "raw data" of the next. “Raw Data are numbers, characters, images or other outputs from devices to convert physical quantities into symbols, in a very broad sense”. Such data are typically further processed by a human or input into a computer, stored and processed there, or transmitted (output) to another human or computer. Data gathered from surveys, or input from several independent or networked locations via data capture, data entry, or data logging.
Data is the backbone in this project. The data is collected from different sources and through different means. On the basis of functionality of the portal, data is collected. The requirement of the project decides what kind of data is needed, what percentage of accuracy is required. Once this is decided then comes the mode of data collection. Mode of data collection means through which process rather how the data will be
from toposheet, journals, and magazines. Now, mode of data collection also depends on certain factors like the budget, the time span, the accuracy required, the skills in hand and vitally the aim of the project.
Here in this Project there are mainly two aspects of data discussed: Primary Data Augmented Data
B
Primary Data
Primary Data-Information that researchers gather first hand. Primary data are facts and information collected specifically for the purpose of the investigation at hand.
All data used should be current, relevant, reliable, accurate, and conceptually correct; this is the aim behind primary data collection. The analyst can obtain primary data through the process of direct observation. The primary data is collected with the help of GPS and Field Surveys.
C
Categorization of data for Portal
Basic Layers which are of importance for Local Search Portal is 1. Point of interest
2. Building layers 3. Road Layer 4. Railways 5. Locality Layer
D
POI (Point of Interest)
These POIs include Spatial as well as Non-Spatial Data. Spatial Data are the entities collected with GPS and the Non-Spatial Data includes the attributes or the information about the POI. For example, a shop is a Point of Interest, the location of the shop is taken with GPS and its Non-Spatial data is also gathered, like what kind of shop it is e.g. Medical Shop, timing of the Shop, the proper address, contact number or any other information is taken into account. Photographs of the POIs are also taken which is the requirement of The Portal and also the “Uniqueness” factor for the Portal.
E
Role of Categories in POI
As GIS data are very use it is very difficult to manage and retrieve data without grouping on the basis of similar attributes, with the help of category attribute, we group data of similar properties. For such we use category list which having unique category name and category code. This category and category code field is added in the every POI, which facilitate us at the time of retrieval of POI. The search data in the Database by unique keyword or code. When user searches POI’s on the basis of category, this category attribute
works as a keyword and this keyword will be linked with their unique category code. This unique code will established link with all POI having this category code. Only the POI having this code will be grouped and it is easier for program to search POI from this group. Therefore addition of category code in the POI helps to improve the efficiency of search engine.
F
Merge and Projection of the data
After categorization, the Shapefiles are there having names like Hotels, Banks, Hospitals etc. All the above information is collected through a GPS need to be merged and projected. Likewise ten GPS use to go with ten different teams and all the ten GPS information need to be downloaded, converted, merged and projected in required coordinate system separate folders to keep a track.
Merge: This function combines input features from multiple input sources (of the same data type) into single, new, output feature class. The input data sources may be point, line or polygon feature classes or tables.
Now, once the file is merged and projected, now other attributes need to be attached to the data, i.e. the survey sheet data. This data need to be typed in excel which will later be converted into DBF and attach to the concerned POI.
G
Data Typing & Editing in Excel
In General Data editing is about detecting and correcting errors in the information returned by the contributors of the data. The entities are collected with GPS, these are the spatial data as well as the non spatial data (attribute data). Attribute data information is collected in Survey sheets and this need to be typed for further processing. The date entry person manually enters the attribute of each feature. The Attribute Data contains Address, Pin No, Category, Facility, Road Name etc of the Individual Entity. It is required that the data should be entered carefully making the least possible manual error, otherwise will result into a serious error at the time of further processing and at later stage.
H
Field Survey Data Collection and Transfer (Primary Data)
Detailed study or inspection, as by gathering information through observations, measurements in the field, by asking questions itself on the field forms the basis of field Survey. The surveyors collect entities with the help of GPS and also fill the survey sheets which acts like the non spatial information about that feature or POI. In GPS they only type the POI name for the identification of the feature. Other information are written in the survey sheet, .The survey sheets consists of fields like POI Name, Address, Phone No., Website, E-Mail, Remarks etc.
At times due to certain technical or other reasons, if GPS do not work, the entities are then collected on the map of the area, numbers are put against those entities, and the area covered and in the survey sheets with reference to that number other non spatial information are entered.
I
Uploading Field Survey Data
The maps on which entities are collected by the surveyor’s needs to be digitized and its attributes need to be entered. This is done with the help of ArcGIS software, in the Arc map, the base map layer is kept on even their labels are kept on, to get an idea of the area. With reference to the base map and the hard copy map, a new Shapefile is created and on that area points are digitized and attributes are filled for the same. Here non spatial data consists of the information brought in survey sheets and also the materials collected by them, like visiting card. So, this is the process followed for making a softcopy of the survey data. A unique id is also generated by adding a field and field calculating a formula for U_ID. This, data further goes for quality check.
J
Augmentation of Data
In this Project data is the integral part and as the days pass by, new entities emerges, as search of the POI is one key functionality for portal, it’s the need to always update the data so that each and every entity of a place is covered. If we have such kind of data, it would be very useful for the portal.
It becomes very difficult to capture all the possible entities of the region, as they keep evolving and also due manual error and other constraints it may not have been collected. But the data should be there, so there is a need to enhance the data.
Augmentation is done generally by two means:
• Data Team Contact Brand Owners/POI Owners
Call from Primary Sources by Phone/ in person • Brand Owner Website
Figure 3(Data Argumentation Process)
III
Methodology
When extra information is gathered from the POI source then it is further checked that whether this data exist with us or not, if exist then it is further cross checked whether we have all information, as getting data from brand source provides complete information.
As said, data is updated through this method. The methodology to upgrade the data is by digitizing the points of the entities and entering the non spatial data and giving it a UID.
Done with the reference of Base Map.
IV
Data Attachment
Now, we have spatial data, non spatial data (also kept in Microsoft Excel), all these data need to be attach together.
Primary Data: We have two different kinds of data, GPS data and Field Survey Data. Field Survey Data is digitized and attributes are entered, so we get proper shapefile. Now, the GPS, in one hand we have spatial data with only POI name and on the other excel sheet having all information. So, these both needs to be attached.
Once this is done all the primary and augmented data need to be merged together in one Shapefile which will have all the data. For that load object tool is used but for that to work the target file which is our master file having maximum fields should be kept in personal Geodatabase and the this tool works.
It should be kept in mind that fields in all the tables should have same property.
Edit
Information
END Digitize the Point and
enter all information as attributes. Check if POI present in the File If Present check all information Yes Yes No Yes Yes
Data Updation
Personal Geodatabase has been used in ArcGIS since their initial release in Version 8.0 and has used the Microsoft Access data file structure (the.mdb file). They support Geodatabase that are limited in size to 2 GB or less. However, the effective database size is smaller, somewhere between 250 and 500 MB before the database performance starts to slow down. Personal Geodatabases are also only supported on the Microsoft Windows operating system. Users like the table operations they can perform using Microsoft Access on Personal Geodatabases. Single user and small workgroups with smaller datasets some readers and one writer. Concurrent use eventually degrades for large numbers of readers.
V
Concept of Load Object
The Object Loader wizard in ArcMap allows specifying a number of source tables and feature classes, provided their schema match. It also allows specifying which fields in the input data are loaded into which fields of the target feature class or table.
A
Basic Layer
• Landmarks (POI) • Building layers • Roadways. • Railways etc.
Other Layers which are of importance for our Local Search Portal are the.
B
Locality Layer
These all layers are prepared in the GIS software i.e. Arc Map 9.2. For this project locality (polygon) layer is created. Here, Locality plays a very important role. This is because when user searches for POI, they actually want to extract information regarding address of that POI and all the related information. If he is looking out for address then it is necessary to provide him with the right Locality of the POI he is searching for. Locality mainly refer to the fact or condition of having a location in time or space, it also refers to a particular place, situation or location.
While Preparing the Locality layer it is necessary to have certain reference that is either taking reference from map available like existing maps or internet or any other source available. Over here Building, Railway station, and Road layers are for reference to draw a locality. Moreover by visually seeing the map, with the help of these reference layers and to a certain extent local knowledge, Polygon layers are drawn on the map and the locality name is given to it. Pin Code information of the Locality is also entered, this information can be drawn from reference layers. Since it is done manually Errors may exist.
For a Locality layer, Polygons need to be made adjacent to one another. The polygons should share a border, in this process manual error can crop in like double digitizing of border, overlaps and spaces between Polygons.
Table 1(Locality Attribute Table)
Thus with the help of the reference and having local knowledge locality polygon layer are made. These locality polygon layers are used for different purpose. In this project of a search portal it is a very useful layer since it would help in providing information regarding address.
Figure 4(Locality Layer)
Filling in donut holes in polygons:
FID UID LOCALITY PIN NO
148 M1_324R Vashi 400703
149 M2_658R Sanpada 400705
Sometimes manually holes get created within a polygon which may be void and null, has no meaning at all. This kind of polygon need to be removed or filled.
Figure 5(Issues with locality Layer)
C
Removing Overlapping and Sliver Polygons from existing polygons in Locality
During the process of Quality check, innumerable overlaid locality polygons are seen. It is required to remove these polygon overlay since area of the polygon is added twice which create problems at the later stages of the Project. Another Error is the slivers or gap between Locality Polygon. Tiny sliver polygons or gaps between polygons often results while creating new polygons without using snapping or editing shared boundaries without a topology.
Slivers and gaps keep your data set from forming a continuous fabric and should be identified and fixed as appropriate. However here to remove these errors Geodatabase topology is used. It is the most efficient, automated, and thorough means of finding and fixing these errors. Here certain rules are chosen to solve these errors. Rules applied are Must Not Overlap and Must Not Have Gaps, to find polygons that either overlap each other or have gaps between them.
Figure 6(Removing Slivers or gaps between polygons and Overlapped Polygons)
Donut Locality Polygon Overlap between Polygons Sliver (gaps) between Polygon
D
Removing false information from the Attribute Table
If the attribute contains false information, it needs to be corrected immediately. Knowing the importance of locality in searching for address of POI, it is required that the information coming at the screen during search to be correct and accurate and therefore importance is given to correct the information available in attribute table of the locality Polygon. For Quality Check of Locality’s Attribute, Map (Hard Copy) and Existing Map are used. The master .shp file which contains Locality Polygon is opened, and manually and visually the Map (hard Copy) is referred and seen whether the name of the area in the Locality polygon (.shp) is correct or not. If it is incorrect, the correct locality name is entered. It should be kept in mind that the referred map or any other reference should be valid and correct.
These are the Errors which need to be corrected while doing the Quality Check of Locality. Quality Check of Locality is a tedious job. After correcting such errors the Shapefile goes to the development Team.
E
Road Layer input for the Portal especially Routing
As per the Functionality of the Search portal is to provide Road Direction to its user. Therefore it is required that Data regarding Roads to be accurate. A Road is defined as an identifiable route between two or more places. The information given by the search portal needs to be correct, it should provide information regarding the type of road, whether there is a junction ahead or not, is it one way etc.
It supports polyline feature classes of ESRI Shapefile, we have to maintain various constraints on the road network and also classify the various type of road, which help to realize real structure of Road for routable search engine.
Classification of Road by Road Type
• Major Road: Road between two cities State Highway, National Highway. • City Main Road: Ring Road.
• City Major Road: Bus route between Localities. • City Minor: Bus Route inside locality.
• Lane: Connecting Road between City and neighboring Town.
• Service Road: These roads are parallel to national and State Highway to distribute traffic. • Slip Road
Classification of Road by Road Class
In our Road network we added very important Attribute Road Class. Road class plays an important role in both Routing application and Map tiling. We assign unique numbers to Road class and attribute for every segment of Road according to their type:
Road Class Road Type
1 : National highway
2 : State Highway
3 : City main Road
4 : City major Road
5 : City Minor Road
6 : Service Road
7 : Slip Road
8 : Turn lane
9 : Dirt Road
F
Vertical Elevation
The attribute Vertical Elevation also placed very important road for routing and map display, we assign road segment in earth surface as ‘0’. And segment inside earth surface -1 and above earth surface +1. This assignment placed important role in Routable routes since at Vertical Elevation at – road which stands for Subway traffic cannot pass through it.
1 Road Name 2 Road Alias 3 Road Type 4 Road Class 5 Oneway 6 Vertical Elevation 7 Road Length 8 Road Width 9 Median Status
G
One way
This attribute restricts flow of direction, it has two values in their domain (0 and 1). 0 stands for two ways and 1 stands for Oneway. If road is Oneway, then flow of traffic will be unidirectional, which cause major constraints for Route determinations.
These are the attributes, which we use in the Road data, for Routing application, and find good in practice.
Table 3(Road Quality Check)
Road Quality Check is as important as locality Quality Check for address. In this project Road plays an important role and it is one of the Basic layer. While creating such multi-line, attribute information is also inputted. The information inputted should be correct. However this is checked during the Quality Check process. The attribute information mainly consist of what type of Road is found whether it is a single junction or a Four Crossing Junction or multi junction, as well as one way etc. In Quality Check the newly created feature’s attribute is checked.
Attribute
Road Name Linking Road
Road Type Single Junction
Median Status N
Shape_Length 47.8
Road Width 20
Figure 7(Removing Errors like dangles)
H
Process of Quality Check for Road
Quality Check of Road is also done. Errors such as dangle, pseudo, must not intersect, must not overlap should be removed. In order to know these errors Topology is build.
As per the functionality of the search portal, the information regarding the road direction needs to be correct and accurate. Thus the modified layer is required to go in for quality check. The First record is selected, and the attribute table is opened. The Road (spatially) shows that it is a single junction, and then in the attribute table of that road, the Road type should be Single Junction. In a similar way other attributes are also checked. Moreover the Road is also checked spatially, there should not be a gap between two roads, if gaps are found it is corrected by using the snapping option. This process which is followed in the Quality check of Roads.
I
Quality Check for Primary Data
Data’s from Primary source may contain Errors, there is no such data which is said to be accurate, and each and every data comes with some kind of Errors. Data quality is largely determined with four generic measures of quality, namely, accuracy, precision, error and the uncertainty that is associated with using data of unknown quality.
In quality Check the spelling needs to be checked, incorrect spelling of POI are to be corrected; for example Mc Donoad should be corrected with Mc Donald, Moreover a consistency should be followed throughout the POIs for example all POI Banks should be in Caps’ i.e. sbi should be SBI, hsbc should be HSBC, all POI should be in Sentence case and in all Capitals where required; No POI should be half i.e. which may have no meaning then example Meena Co. this should be corrected to either Meena Company or Meena Metal Co-operation whichever valid. Category of each POI is checked. Each POI should belong to proper
category i.e. Sacred Heart Hospital should not fall under Category Hostel but should fall under Hospitals. Addresses are checked accordingly. Phone No are checked by giving calls and finalizing whether it exist or not and is it valid and also checking through internet and directory. Website of each POI is checked in the internet to see whether the website is corrected or not and from the website we can derive more information and cross check it.
Figure 8(Data Quality Check)
Thus each and every POI goes through the process of Quality Check and this Quality check is done in every step. Once these data are passed through Quality Check it goes into other stages of the project. The quality of data which the user would see at the end would mainly depend upon the quality check of the data. All the hard work will go in vain if data quality is not good.
Quality Check is done in all the Stages and keeping in mind certain things.
Start from Field Survey and collection of data from GPS.
Augmented Data: Check is also kept on correcting manual errors as this data is collected from the information by brand owner itself hence it’s reliable.
During the typing of the data
Check on the double entry of data
Making the data error free
Proving all possible correct information.
Spatial and Non-spatial data to be truest in all regards
The data should be the kind of what is expected out of the Portal. It should fulfill the aim of the Data Quality
Check
Spelling + Address + Categories + Email + Phone No + Website etc
Yes
Goes to Next Stage
No
Recheck & Corrected
Figure 9(Example of Photo ID Quality Check)
The attribute table of the spatial entity contains photo Id no. which may belong to the Photo number. Moreover each POI Name has a Unique Id Number. This UID is said to be one and only ID which links different table. Thus during quality check both the Image as well as the table is open side by side, and visually the POI name is checked with the Photo. Suppose POI Name is State Bank of India then during QC. The operator searches the photo number and see’s whether the image is correct or not if it is correct then the UID of its POI Name is given.
VI
Database Management
A
Database
A database is a structured collection of records or data that is stored in a computer system.
A database management system (DBMS) is a collection of interrelated data and a set of programs to access those data. The primary goal of DBMS is to provide a way to store and retrieve database information that is both convenient and efficient. Now one of the most challenging jobs is to manage the database, because at lower level of abstraction we have all the information spatial and Non-spatial in the form of shape file, and shape file is not compatible for the web application. For this we have to convert this shape file into web compatible database format. For this purpose Oracle (spatial Feature), postgreSQL can be used.
This PostgreSQL database is not faster compare to SQL Database. Therefore we keep spatial features in to PostgreSQL and non spatial data in to MySQL ,for fast retrieval of data.queries related to Non-spatial features will hit MySQL server and having spatial feature will hit PostgreSQL database server. Spatial feature of Database is stored separately for Routing in Routing Database (PostgreSQL), and Non-spatial feature is stored in Web Database (MySQL).
B
Convert Shapefiles into Postgre Database files
shp2pgsql [<options>] <shapefile> [<schema>.]<table> > sqlfilename.sql
Example:
shp2pgsql -c street.shp street_table my_db > street.sql
PostgreSQL stores data in two Database Server
C
Routing Database server
This Database server stores only the data which is used by routing algorithm.
Routing algorithm uses the attributes road name, road class, vertical elevation, road length, road type. All this information are extracting from road layer of our project. Routing database server is designed in PostgreSQL, because of storing spatial features.
D
POI database
This database server stores the spatial information of the POI, and link with web database server. It is also designed in PostgreSQL.
E
Web database
Since PostgreqSQL is not fast as MySQL, therefore web database that stores Non-Spatial data in the form of SQL file, link with POI database server.
Since non spatial information is so large, therefore for making this application faster, establish link between POI database and web database server.
Spatial information of POI is retrieve from POI data base and attribute or non spatial information retrieves from web application
F
Web Application
Is an application that is accessed via web browser over a network such as the Internet or an intranet. It is also a computer software application that is coded in a browser-supported language (such as HTML, JavaScript,
Java, etc.) and reliant on a common web browser to render the application executable.
G
My SQL Admin
This is admin database, performing administrative operations. You can use it to add and update the POI data as UGC (User Generated Code) and to verify the all information about the POI data.
Figure 10 (Overview of Database Architecture)
VII How use GIS data for Routing
The next thing which the project focuses is on the road network for Routing, which is one of the major Functionality of the Portal. And so it is necessary to build up a Road network for it. Now, what is a Road Network? A road is an identifiable route, way or path between two or more places. Road network over here is to know the direction of the Destination from the Start Point turn by turn. It refers to the any interconnected roads which may provide information as to the direction to the destination. The input data are the road network.
Routing Application is not challenging task in the paper, but to represent routing routes in the web application is challenging task. In this case study we explore various
technologies for routing application to represent in the web, these are PostGIS, and pgRouting.
Complete Database Routing Database POI Database Web database Web Application Search Applicatio Routing Applicat ion
PostGIS is an extension of PostgreSQL object relational database system that allows GIS object to be stored in database. There are several open source tool are available which work with PostGIS, we proposed and find good in practice for internet mapping, the university of Minnesota Mapserver can be used PostGIS as a data source, and displaying the output on the map for Routing Application. There are various languages which can work with PostgreSQL along with PostGIS (like Perl, PHP, Python, TCL, C, C++, and JAVA). But in this case study we have using Python and PHP, which is easier to implement and efficient for applications.
A
pgRouting
Every routing application requires source and destination. And there are several paths between a source and destination, but shortest path between source and destination is always part of interest. Therefore every routing engine requires the source and target nodes for every line in order to create a search for the shortest path. For this we have to road networks, which involve creating a topology on this network. In this case study we use Arc Info for building topological coverage file,and then export this coverage to a shape file, which can then be imparted into PostGIS. On creating topological coverage three columns are automatically added these are
fnode, tnode_, length columns.
Where fnode stands for source node, tnode stands for destination node and length column stands for initial cost.
This can be renamed in PostgreSQL into source and the target, length can be set as initial cost. pgRouting adds the routing functionality to PostGIS
Navigation for road network requires complex routing algorithm that support turn restrictions and even time-dependent attributes. PgRouting is an extensible open source library that provides a variety of tools for shortest path search. The library in its current version is an extension of PostgreSQL and PostGIS. Its predecessor “Dijkastra” was written by Sylvain Pasche from Cromptocamp, it was then extended by Orkney (Japan) and remained to pgRouting.
B
Database Routing approach with pgRouting
Since most of the routing algorithm works on the greedy algorithm, greedy approach reuires cost from one node to another at run time, for finding shortest between source and destination. pgRouting have capability to calculate cost between two nodes dynamically, and can produce result for web application at run time. By adding pgRouting and PostGIS functionalities to our Routing database which is designed in PostgreSQL, we obtained sortest path between source to destination in sql format. This output file can be represented with various web mapping server like Mapnik, Mapserver etc.
Figure 11(Routing Architecture)
VII How use GIS data for Map Application
It is revolutionary to represent a map on the web dynamically. In this era everybody wants to get the information visually and dynamically. We use ArcGIS to generate map digitally in the form of Shapefile or Coveragefile. Still there are not any efficient ways to show ESRI Shape or Coverage file to show in web directly.
Therefore we have to generate a Map from Shapefile to such format which can be easily handled for Web application. For this we use Open Source technology Mapnik.
Mapnik is an Open Source C++/Python toolkit for developing Mapping application. At the core is a C++ shared library providing algorithms, pattern for Spatial data access and visualization. Mapnik uses Shapefile to create Maps in PNG, JPEG, GIF etc. Since Mapnik reads XML to generate map. This XML passes through an interface. This interface is created with Open Source language Python or any other scripting language. This XML file is to be generating on the basis of Mapnik standards. This XML have information which is required for map generation extent, zoom level, Shapefile name, Datapath, Datasource, features etc. Therefore we first generate XML, for efficient generation of Map for a Portal. We generate various maps for various zoom levels. Every zoom level has some specific Spatial feature. Therefore we extract the Spatial features for different zoom level and divide our Shapefile into many small Shapefile. We have to write configuration file (CFG) for various zoom level. Theses Configuration files have the information about Map, Style, Layers, Datasource, and Rule. These CFG is converted into XML through XML generator (script).
PostGIS
Shapefile
PostgreSQ
L Database
Web
Application
Mapserver
Routing
Table
pgRouting
These XML file passes to Mapnik, which results Map into PNG, JPEG, GIF as per our requirements. These formats are easily rendered for web application, and an efficient way to generate a Map from GIS Shapefile into Web compatible Map format.
Figure 12(Data Flow for Mapping Application)
Shapefile
Web ApplicationPNG Map
Configuratio
n File
Generato
XML
r
Mapnik
Tile CacheFigure 13(State Boundary of India)
A
PNG generated by state boundary Shapefile
CFG File Format For above state boundry png
[state_boundary] placement_type = polygon line_color = #cbcbcb# color = #fbf5f1 width = 0.8 datapath=/dabb12/tile_56/city_png/city /All_data/stateboundry_gd
CFG for National Highway
[national_hwy] placement_type = line
filter=ROADCLASS:=:0 or ROADCLASS:=:1 color = #ff9933
datapath = /adcd/tile_57/city_png_1/city/All_data/road_gd
VII Conclusion
As main challenge is to understand creation of GIS data which is compatible with search engine portal. Such type of data should be accurate and precise and also maintain integrity and consistency.
Various issues occurred while handling such huge data, procedures discussed above
Gives an overview how POI data, Road Data, Locality Data should design and how it can be made more useful for search portal. Discussed procedures are finding good in practice.
Compatibility between different technologies like ArcGIS, Python, PostgreSQL, pgRouting, Mapnik is being established by various experiment and study. These technologies can be helpful to design and implement local search portal based on GIS data, where user find result graphically on map with lots of description.
References
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Books
1. Concept and Techniques in Geographic Information System, by C.P. Lo and Albert K.W. Yeung (August 2006).
2. Database System Concepts 5th Edition, by Avi Silberschatz, Henry F. Korth, S. Sudarshan (May 2005).
3. Beginning PHP and PostgreSQL 8 from Novice to Professional, by W. Jason Gilmore (Mar 24, 2008).
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Manuals
ArcGIS 9 Using ArcGIS Desktop (2006) ERSI ArcGIS 9 What is ArcGIS 9.2? (2006) ERSI
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Internet
http://en.wikipedia.org/wiki/Global_Positioning_System
http://www.trimble.com/gps/index.shtml
http://en.wikipedia.org/wiki/Server
http://www.google.co.in/search?hl=en&q=ORACLE+NETWORK+MODEL&meta= http://en.wikipedia.org/wiki/Oracle_Spatial http://www.gisdevelopment.net/ http://en.wikipedia.org/wiki/Oracle_database http://trac.mapnik.org/ http://mapserver.org/introduction.html#an-introduction-to-mapserver http://www.python.org/psf/