Thomas P Newdome and David L Bynum
SDE and MapObjects Evaluation For Transmission Data
The paper reviews the findings of a project which built an SDE database which contained lines, switch, substation and landbase information for Alabama Power transmission facilities. A Visual Basic application was coded, using MapObjects to access and display the data from an NT client. The paper outlines the basic data and system architecture, and reports on the performance measurements taken by the Southern Company Services Application Testing Lab.
Figure 1 - The TransGIS Application
I. Introduction
A relatively large amount of geographic data has been gathered over the past few years within the Southern Company. This includes Corporate Real Estate, Telecommunications, Power Delivery - Transmission and Power Delivery - Distribution information. Several efforts have been made to provide general access to this data, with varing degrees of success. However, there has been no effective method of providing access to this data within the Company desktop environment to a large numbers of users.
Esri has introduced a new product, Spatial Database Engine or SDE, which is marketed as a solution to manage large Geographic Information databases. Both the graphics and attribute information is stored in the same industry standard relational DBMS. SDE is the server portion of a true client/server environment. Esri currently has three products that can provide the client portion of the environment. Two are developer tools. One is a programming library for the C language that provides all the API's that Esri uses in their products. Another is a 32 bit OCX, Map Objects, which can be used with Visual Basic, or other tools that support the use of OCX's. The third product is the latest version of ArcView. ArcView 3.0 is an end user tool but can be customized using a scripting language. The next version of Esri's ArcInfo will be a full SDE client. Also, Esri's stated direction is for SDE to become the data management tool for all their products.
After doing preliminary reviews of this software, Power Delivery and Corporate Real Estate at Alabama Power Company requested that a formal review be done by Information Resources.
II. The Project
Purpose
The purpose of this project is to evaluate SDE and Map Objects and gain "hands on" experience with the products. Short term needs of some departments within Alabama Power Company as well as long term strategic GIS initiatives may be addressed if SDE and Map objects prove capable of providing certain functionality. SDE must be an effective server and data repository of geographic information and Map Objects must provide reasonable query functionality and high speed display using standard tools such as Visual Basic.
Objective
A technical evaluation of SDE and Map Objects in a client/server environment was performed in order to determine the feasibility of future use as a GIS tool for the desktop. This evaluation consisted of the construction of a very simple SDE/Oracle database on the server side, and a prototype Visual Basic viewing program as the client incorporating Map Objects as the connection to SDE. The functionality was very limited, including only pan and zoom, and simple query of two data types within the database. Other data collected was network impact and resources required to establish this type of environment.
SDE Database Design
It was fortunate in that a database design for the transmission facilities had been previously performed in which the required entities (point and arc features) and their respective attributes had been identified. Further, this definition included the appropriate look up tables for feature attribute validation. This definition was utilized in creating the SDE database design.
Input of data
The data had been digitized as a coverage in native ArcInfo 7.0.4 utilizing the 7.5 minute quads as a reference source, along with known GPS points. The data was extracted as an ArcInfo 7.0.4 coverage and exported as shape files for arc features and point features. These shape files were then imported into the SDE database with all layers in the same dataset.
System Configuration
The development environment for the desktop was the 32-bit version of Visual Basic 4.0 using the Esri MapObjects OCX. The server environment was the Sun Solaris 2.5 operating system, Oracle 7.3.2.2.0 and SDE 2.1.0. This software was running on a Sun SPARCStation 20. The desktop environment was a standard desktop (Pentium 90 or better with 32 MB memory) using either Windows NT 3.51 or Windows NT 4.0.
Coding of Visual Basic Application
Visual Basic 4.0 32-bit and the MapObjects sample applications were used to create a Transmission / Land Data Viewer with the following functionality: pan, zoom in, zoom out, find, identify and print. All the functionality was contained in the OCX; minimal VB code was used to effect the required functionality. After learning the OCX, the viewer tasks were easy to perform ... resulting in a 6 man-week effort to complete. With current knowledge, we feel we could cut this time in half. The resultant graphical user interface is shown in Figure 1.
Testing Results
Overall results were positive in the areas of user performance and network testing.
The performance of the application, for the purpose of testing, was subjective and judged as sufficient. The shape file source for the SDE database consisted of 352,240 features and 4,088,779 attributes, including 7,673 features and 298,956 attributes associated with the basic line and switch information for the entire Alabama transmission system. Time to draw a typical view of features in the database, using the application front end across the network took approximately 15 seconds. A typical query to locate a switch in the database took approximately 3 - 5 seconds.
The application was also subjected to formal testing in the Business Applications Test Laboratory (BATLAB). The test consisted of running various functions of the application while monitoring traffic between the NT workstation and SUN server. The main traffic was 8 bytes (data) sent in one direction and about 16,700 bytes (data) returned at a maximum rate of six times per second. Overall, the application, as is, was judged sufficient for a local area network, based on current constraints. For WAN use, the TCP window of the client may need to be reduced in order to have less impact on other traffic. Time constraints prohibited further testing which will be needed in regards to the WAN.
Experience was gained in the "hands on" use of MapObjects and setting up the SDE database. No major difficulties were encountered. If a deployable application is pursued, a thorough design of the database layers would probably be needed to insure support of system business needs such as access and use by other SQL based applications. Further, functionality would be required to connect to multiple datasets on multiple servers.
III. Summary
In order to gain hands on experience and determine initial responsiveness of SDE based data and MapObjects, a demonstration application was developed using Transmission data from the Alabama Power system. Although further testing is needed in regards to Wide Area Network issues, indications are that SDE may be a suitable data server for large datasets. Experience was gained in the use of an industry standard development environment to perform access through the Spatial Database Engine.
Thomas P Newdome
Supervisor, Methods and Systems 10N-0735
Alabama Power Company
600 North 18th Street
PO Box 2641
Birmingham, AL 35291
Telephone: (205) 257-4268
Fax: (205) 257-4327
E-mail: tpn@ix.netcom.com
David L Bynum
Sr Engineer, Methods and Systems 10N-0735
Alabama Power Company
600 North 18th Street
PO Box 2641
Birmingham, AL 35291
Telephone: (205) 257-4242
Fax: (205) 257-4327
E-mail: david.l.bynum@apc.com