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The DK Used in an Environmental Application to Model the New York City Regional Estuarine System

November 18, 2002

The following is a detailed description of a GIS system created by the U.S. based environmental engineering company, HydroQual, Inc., with the use of the TatukGIS DK. The GIS functionality created from the DK includes data mining and graphic presentation functionality, including time-line animation, to assist engineers with their work in the area of water quality engineering, consulting, and the preparation of environmental impact assessments. This GIS system is presently being used to model and analyze the water quality in the bays, reservoirs, estuaries, and rivers in the New York City region, and elsewhere.

GIS Interface for State-of-the-Art Natural Waters Modeling
By: Gary Ostroff

HydroQual, Inc. (www.hydroqual.com) is a water quality engineering and science firm that develops detailed computer models of natural water systems (bays, reservoirs, estuaries, rivers, etc.) to evaluate environmental impacts and proposed pollution control measures. These models allow our clients to assess the merits of proposed engineering alternatives, and they assist us in determining the causes of difficult water quality problems. Over the last twenty-five years, the firm has constructed several models of the regional estuarine system in the New York City region - an area of great variety and complexity - and the model produces voluminous output that must be absorbed by our engineers. We have employed TatukGIS to create a complete visualization and animation system that gives engineers a window into the enormous amount of data to be evaluated as part of our efforts to protect the waters surrounding New York City.

The model that HydroQual has developed employs a network of cells, or a grid, overlaid onto the geographic region. This two-dimensional grid is then expanded to 3D by dividing the water column into ten distinct layers from the surface to the ocean bottom. The simulations of this area are for periods upwards of a year or more, for scores of hydrodynamic and water-quality parameters (e.g. dissolved oxygen, biochemical oxygen demand, chlorophyll content, etc.), calculated at a time-step 10 minutes or less, with the results saved on a daily or weekly basis. Thus, the engineer is faced with model output that varies in map-space, in depth, in time, with regard to multiple parameters. Ideally, the tool that provides an interface would allow the engineer to 'slice' the grid in any direction, for any given time, for any parameter of concern, and see the result mapped and graphed. In addition, time-series animation is a crucial tool for both analysis, and communicating results to the clients.

HydroQual has developed a proprietary system that is used in-house to plot data in myriad ways that are especially useful to our staff. We have also developed a visualization system to create and display animations, but it does not easily integrate GIS data, and it is not a full-scale data mining tool that would allow engineers to diagnose or present their model results. HydroQual has experimented with other GIS applications to meet these needs, but two elements always stymied our efforts: system performance; and the need to represent time-series data. Our current efforts with TatukGIS, using ADO technology, have eliminated these problems.

The philosophy behind the design of our new HydroQual Modeling System (HQMS) is to use off-the-shelf technology for each specialized task. Thus, the TatukGIS object library, in a Borland Delphi6 environment, provides us with all the tools we need to create standard GIS functionality that gives superior performance. These functions include:
  • Read standard GIS data formats, especially shapefiles.
  • Pan and Zoom on a map view, scale display
  • Report map coordinates and local data in real-time
  • Display registered images for context - satellite imagery, scanned nautical charts, etc.
  • Create thematic legends with symbols, color, statistical intervals, etc.
  • Arrange layer order, modify transparency of layers
  • Label features with attributes
Not only do the TatukGIS objects provide these functions, but the performance of the objects, even when running in the debug mode, is superior. We were particularly impressed by the speed of the labeling functions, and the ability to display only a slice of the grid by applying a simple SQL query to the shapefile. We also interactively varied the SQL string, and found that as the slice moved, the labels would move with it.

By storing our model output in an .mdb object, and joining it to the shapefile using ADO objects, we were able to place the burden of processing time-series data on the elements that do it best, and then simply display the results in thematic maps and graphs. The Delphi environment provides a powerful set of tools for implementing a variety of section and transect graphing functions, all based on ADO queries of the underlying database. Finally, by simply altering the SQL strings, we were able to extract a series of data-views, varying with time, and map them. The animation proceeds without screen flicker, and all elements of the display, graphs, color, and labels, can easily be made to vary in synchrony with the time-series data. The images below give some sense of the versatility of the application:

The image to the right shows a close-up view of the New York Harbor, with the modeling grid superimposed over a NOAA nautical chart. The grid has been made partially transparent so that sounding data may be read for individual cells. Note the scale and coordinate display at the bottom, and the reporting of cell (I, J) values for each model cell. This is a crucial identifier for diagnosing and calibrating all large water quality models.


The images to the left show some of the versatility of the display options available in this application. The general view of the NYC region has been color-coded as a thematic map of salinity. The model grid is displayed in real geographic space, and in model space as the computer 'sees' it. (Salinity varies little, except in the estuarine rivers, e.g. the upper reaches of the Hudson that appear blue in the map.) The parameter control form can be used to alter the display so that salinity at any model layer is displayed, and the values may be varied by time. The form also allows the user to rapidly change the parameter being displayed from a standard list box. With these tools, the analyst can quickly map any variable, for any depth, for any time-period of interest. (Running on a standard laptop computer, the system was able to map data for an entire year's simulation without noticeable delay.)

The image below shows how the system can be used to select specific rows and columns of the model grid, mask the others, and plot the values of the parameter of concern (e.g., depth, DO, salinity, etc.) on accompanying graphs. The user can click the arrow buttons to interactively move the transects up and down, left and right: the plot follows suit.

The very rapid response of the system is achieved by employing SQL calls to the .mdb object to extract the required data for the charts. The map window simply illustrates the areas of interest, and can be used to interactively define them. A similar technique is used to generate plots for any parameter that varies with time by clicking on a single grid cell of interest. The plot at the left shows the variation in salinity for the surface layer of a cell in the lower Hudson River, with ten-day average values. The quality of the graphics that are available in the Delphi environment far exceeds anything we have seen in standard GIS packages.

Finally, animation has always been a serious tool for analysis and client communication on many types of HydroQual projects. The image below shows the simple tool used to initiate a one-year animation of the model results. Only a single transect of interest is displayed, and both the thematic colors and the labels indicating the numerical value of the parameter change with each time-step. The user can select a parameter and a depth level, and then animate the stored model results using any preferred time-step, e.g., one-day, ten-day, one-month, etc. Needless to say, the ability to employ these tools in conjunction with the standard GIS ability to display and select from a wide variety of data, e.g., imagery, census data, water quality measurement points, etc., makes for an extraordinarily rich data environment in which to calibrate and fine-tune our models.