Strategies for Interoperation between a Network Modeling System and a GIS
Gary R. Graybill
Stoner Associates, Inc., P.O.Box 86 Carlisle,PA 17013
Abstract
This paper will explore various techniques and difficulties which must
be overcome to share data between a GIS and a pipeline distribution
network modeling system (NMS) . Hydraulic analysis, one of the most
demanding applications for pipeline facility data, is possible only if
strict topology rules are enforced and the data has nearly perfect
accuracy.
After the structural and accuracy requirements have been addressed,
there are numerous software development tools and strategies to
consider. The resulting software can be used to facilitate bi-directional
transfer of data between the GIS and the NMS. Four
different interfacing approaches will be explored, along with a
discussion of tools, methodologies, and other technical issues.
Introduction
Basic Hydraulic Analysis Model Requirements
Geographic Information Systems that are designed to store and manage
pipeline facility data will typically contain the following types of
attributes:
Typical Piveline Facility Attributes Used For Hydraulic Analysis
- Facility Identifier
- Pipe Diameter (Nominal or Actual)
- Pipe Material
- Pipe Length
- Year of Installation
- Year of Rehabilitation
- Type of Rehabilitation
- Measured roughness/friction
- Pressure level/zone
Missing values for any of the above attributes may degrade, or even
prevent data from being used by the Network Modeling System (NMS) . The
transfer process should have a provision to provide replacement values
for attributes that are mandatory, or required to be non-zero in the
NMs. Values that are selected as replacements should be close to the
acceptable range, but be uniquely identifiable as having been
substituted. Using this strategy will assist in the detection and
manual replacement of these values within the NMS.
Spatial Issues of Networks
Connectivity is one of the most critical requirements necessary for the
use of pipeline facility data in a NMS. If the model is to generate the
correct results, then it must correctly represent the facilities that
are found in the field. In pressure/flow modeling, any molecule of gas
or water must be able to travel the same path within the model, that it
could take within the real-life pipeline system. If enough mis-representations
of pipeline connectivity occur within the model, the
results generated by the analysis would be to inaccurate for use.
Accessing the GIS data
Native GIS Customization Languages
Many GIS systems provide very effective capabilities to access the
underlying data in its native structure. Examples include ESRI’S
Arc Macro Language (AML), Smallworld’s Magic, Autocad’s Autolisp and
Bentley Systems’ MicroStation MDL.
Database Extractions
This approach to transferring data to the NMS uses an export, or “dump”
file, as the transfer mechanism. Once the export file structure is
understood, all the information that is needed must be parsed and
separated from that which is not needed. Examples of this type of
format include ESRI’S shape files, SHL *VISION systems GINA, and
Intergraph’s Standard Interchange File (SIF) .
In an effort to move toward open systems, many GIS vendors have provided
support to read and write new file formats. Some of these formats, such
as the Federal Government’s Spatial Data Transfer Standard (SDTS) , have
been well defined and extensively documented. Software can be written
to directly access the export file’s facility data, if it is sufficient
to meet the needs of the NMS.
Hybrid Systems Data Access
Some GIS systems integrate existing commercial software into their
product functionality. Example configurations of these integrated
systems include CAD systems as a “front end” to the GIS, or a commercial
relational database(RDBMS) as a “back end” to the GIS. Accessing data
in this type of environment may ultimately provide advantages if
specialized multiple data gateways are used.
Dealing with multiple access data gateways, or moving data from one
component to the other, are also some of the disadvantages of hybrid
systems. As an example, if facility data is accessed through the RDBMS,
then spatial data must be moved from the spatial repository to temporary
tables in the RDBMS before it can be transferred to the NMS.
