- Email: [email protected]
Development of a workstation environment for the assessment of a stormwater drainage fee
~1
Review of~~to~‘c
Printed in Great
Pro~r~.~g
vol. 16, pp. 21-27,1992
Britain. All rights reserved
~4138~~15.~ 0 1992 PergamonPress Ltd
DEVELOPMENT OF A WORKSTATION ENV~ONMENT FOR THE ASSESSMENT OF A STO~WA~R DRAINAGE FEE E. H. Kienegger 2i TECH G&H, Schwanthakmtr. 143, D&W0 Munich 2, Germany
ABSTRACT The design and development of a workstation for the assessment of a stormwater drainage fee based on built-up surfaces is described. The work was performed under contract to the City and County of Denver, Colorado, USA. The requirement for such a system was prompted by the City’s decision to institute a fee for the expansion and m~nten~ce of the City’s sto~water drainage system. This fee should be based on the total mount of impervious surfaces (i.e. buildings, driveways, sidewalks) on the different properties. To determine the impervious areas on a parcel by parcel basis a method was selected that employs aerial photography in combination with existing property boundaries available on hand drawn assessor maps. Project requirements, setup and organization, and the implementation of the user requirements are briefly described. Subsequently, the strengths and weaknesses of the chosen approach are reviewed followed by a discussion of the experiences gained after more than three years of operation at the user’s site.
PROJECT HISTORY AND OVERVIEW Due to heavy development and expansion, the City and County of Denver was faced with mushrooming costs for the development and maintenance of a large sewer and wastewater system. To cover the expense of that development, the City introduced in 1980 a service charge to be paid by owners of properties that benefit from the wastewater system. The basis for determining the amount of the charge is the amount of built-up (impervious) area on a particular property. The higher the percentage of impervious area compared to the total area of the property the higher the service charge: A large con~butor to the water runoff problem would therefore make a higher contribution to the development and maintenance of the storm sewer system. A computerized billing system was implemented and a database generated based on existing assessor information about ownership and size of lots, and buildings on those lots. At the same time an effort was initiated to capture the impervious information per parcel more accurately since information about add-ons to existing buildings, driveways, or sidewalks was unavailable from existing records. The necessary measurements were performed manually by city inspectors. Soon the City became aware that the manual measuring method was not efficient enough to cover all parcels within the City in a reasonable amount of time. One inspector would perform four to five inspections per day, and four inspectors would capture the information of about 16 to 20 parcels per day. Considering the approximately 165,000 properties within the City of Denver, a rather formidable task was to be accomplished. Assuming 235 workdays per year, the information for about 4700 parcels could be obtained annually (assuming an average collection rate of 18 parcels per day), leading to a task that would consume approximately 40 years. Consequently, alternative methods were evaluated that would provide the necessary accuracy and accelerate the data gathering process by a factor of 10, thus reducing the time for completion to about three years. It was concluded that aerial photography would be the most versatile source of information for the task at hand. To support the capture of impervious areas baaed on aerial photographs, and to develop a strategy for ongoing database updating a project was started in March 1987 to develop a workstation that would provide the necessary functionality.
User Scenario The workstation to be developed had to support the following work scenario. An operator selects an aerial photogmph from a roll of p~~g~p~ mounted on the film scanning system. After registering the photog~ph to the film plane of the device
E. H. Kienegger
22
via its fiducial marks, s/he moves the CCD camera of the scanner under mouse control over the photograph to select a segment of the photograph at the desired resolution. The chosen segment is digitized and loaded into the memory of an image processing subsystem. In a next step the corresponding vector information is extracted from the geographic database and overlaid onto the image. Discrepancies between image and vector data can be removed by identifying additional tie points located on corresponding features in image and vector overlay. Supported by the overlaid vector information, in this case property boundaries, the user outlines and labels impervious areas such as buildings, driveways, and sidewalks. Once the data collection for the segment is completed the user either selects a new segment, moves on to another photograph, or quits the session. Using this approach the impervious surface information for the City can be captured photograph by photograph.
Develonment
Tasks
For the realization of these requirements
the development
of the workstation was divided into the following tasks:
Software modules . photogrammetric module for registering photographs to the database; . graphic editor to support the acquisition of vector data from raster images; . algorithms for the computer assisted detection of object boundaries in digital imagery; . user interface and message handling; . device drivers (e.g. digitizing board, voice recognition device, film scanner); . interface to third party Geographic Information System (GIS) and Relational Database Management System (RDBMS). Hardware . development of a computer controlled optical zoom system consisting and zoom lens for the digitization of segments of aerial photography; . integration of the workstation components.
of a CCD area array camera
Data . . . . . .
conversion of the existing assessor maps into digital form (vector data); creation of a seamless data set in a standard map coordinate system; transfer of the information into a third party GIS database; production of a set of B/W aerial photographs; organization of photographs into continuous flight lines covering the entire area of the City; control point selection for registering the photographs to the basemap.
Coverage for entire
Geographic Database (spatial and attribute data)
Film Scanning
system
Local Database
Joystick control
USU
Coverage for image segment (
Mouse
Modified coverage for image segment
coverage for image segment Fig. 1.
Overview of data flow and software modules
Develcpmeotof a ~~~~on
E~v~onment
23
The interaction of the different software modules is illustrated in Figure 1. Once a particular photograph has been selected
and registered to the film plaue of the scanner, the vector data corresponding to the photograph are downloaded to the local database for improved data access. Now the user selects a segment of the photograph using a joystick to control the position and resolution of the CCD camera. After digitizing the selected image segment, the corresponding vector data is retrieved from the local database and overlaid onto the image. During the overlay operation the vector data are distorted to match the geometry of the image data. Thls transformation is based on a previously performed exterior orlentation that registers the photograph to the basemap. The registration process is performed during a preprocessing phase where all ~o~gmp~ are registered to the basemap based on control point information. Remaining mismatches between image and vector data can be removed through additional tie points establishing a local transformation. In the next step the user identifies a parcel to be worked on and outliies and labels impervious surfaces using mouse and digitizing pad. After the ifiormation of all parcels within the chosen segment have been captured, the user moves on to a new segment of the photograph. Using this approach the data of the entlre photograph can be extracted. Whenever the user selects a new photograph or quits the current session, the newly collected data are transferred from the local database back to the geographic database of the third party GIS. For the ~plern~~~on of the required functionality, the hardware envi~~ent depicted in Figure 2 was chosen. The various hatdware perlpherals are grouped around a Dee MictoVax II. Interactive film scanning is provided by a me~~tion light table and a computer controlled optical zoom system with integrated CCD area array camera. The anaIog video signal output by the CCD camera is transferred to a Gould FD5000 image processing system capable of digitizing the incoming signal in real-time and storing it in its internal image memory. The digital image is displayed on a separate image monitor. The user interacts with the system via Video Display Tetminal (VDT), digitizing board, joystick, and an optional voice input device. A video printer is connected to the image monitor for instant color hatdcopies. The hardware interface to the billing system hosted on an IBM mainframe is realized through a data conversion device. With the exception of the optical zoom system off-the-shelf components could be used.
I
Storage subsystem (Tape, Optical disk)
I s
1
Interface to IBM mainframe
I
1
CCD array camera with computer controlled zoom lens
Pig. 2.
Hardware environment of Photostation
In addition to the software and hardware environment, the initial set of data required for system operation has to be provided. Thus the 420 assessor maps coveting the Clty of Denver had to be converted into a digital basemap. For this purpose they were manually digitized by a subcontractor. Subsequently, the individual data files (one per map sheet) had to be transformed into a standard map coordinate system and edge-matched to obtain a seamless data set. Approximately 1200 aerial p~~gm~ at a scale of 1:3,600 were produced by a second su~on~ctor. In a preprocessing step the p~~gmp~ were organ&d into flight lines running North-South and registered to the basemap by identifying ground conttol points on common features in photographs and basemap.
Qrganlzation of Develonment Tasks The project tasks required to implement the described functionality wefe divided into a number of work packages @VP)and dlstrlbuted between the member of the development team. The work packages and the cozening man power to perform
E. H. Kienegger
24 the work are listed in Table 1.
The work packages were distributed between six software and two hardware (i.e. one electrical and one mechanical) engineers. Total development time was about five person-years excluding WP9 and WP11. The creation of the basemap and the registration of the photographs to the database required more than three person-years.
Table 1. Workpackages
and required man power
Resources
Tasks
WP
Development of the user interface, message handling, and device driver software Development of local database Development of the photogrammetric software, geometric transformations and data acquisition tools Design and implementation of algorithms for the computer assisted object boundary detection Development of the computer controlled optical zoom system Development of driver software for zoom system Implementation of link to IBM hosted billing database Manual digitization of existing assessor maps Creation of the digital basemap based on digitized map data Production of aerial photography Registration of photography to basemap
1 2 3 4 5 6 7 8 9 10 11
MM . man months;
Table 2.
12 MM by 1 Eng. 6 MM by 2 Eng. 16 MM by 1 Eng. 12 MM by 2 Eng. 8 MM by 2 Eng. 2 MM by 1 Eng. 2 MM by 1 Eng. subcontracted 36 MM by several Tech. subcontracted 2 MM by 1 Tech.
Eng. . . . Engineer;
Tech. . . . Technician
Summary of project related data
March 1987 May 1988 Aug. 1988
Project start System delivery Acceptance Test Resources SW&HW development Database creation
5 person years 3 pctson years
Development environment Platform Operating system Programming language
Dee uVAX II VAXIVMS Pascal
Project management Tool Cost, task, problem tracking Reporting
MicroPlanner (Apple MacII) weekly project meetings monthly progress reports
Third Patty components RDBMS GIS
Oracle (Oracle Corp.) KGIS (Kork Systems)
Subcontracts: Manual digitizing of Assessor maps Aerial Photography
Development
Environment
and Project Management
The development environment was provided by the VAX/VMS operating system. No software development tools other than debugger and text editor were used. The software system was implemented using the PASCAL programming language. A
Development
of a Workstation
Environment
25
summary of the project data is provided in Table 2. Project planning, task estimation, task tracking, and progress reporting was supported by a project management tool (MicroPlanner on an Apple MacII). Weekly project meetings were held to discuss problems, check progress, and adjust the project plan if necessary. Monthly progress reports were sent to the customer to report on project status.
PROJECT RESULTS
AND EXPERIENCES
The development effort resulted in the system PhotoStation shown in Figure 3. Figure 4 illustrates the field of view of the zoom system in overview mode with superimposed parcel boundaries. An example of a completed parcel retrieved from the database using the revisit function of the system is shown in Figure 5.
Fig. 3.
Fig. 4.
Original implementation
of PhotoStation
Segment of aerial photograph in overview mode with overlaid property boundaries
Fig. 5.
Segment of photograph showing measured parcel and impervious areas
E. H. Kienegger
26
The data collection rate achieved by the users operating the system averaged about 100 parcels per day. After adding a second workstation in March 1989 the collection rate doubled to about 220 parcels per day. This lead to the completion of the first time data collection in January of 1992. When compared with the originally used manual field measurements, the data collection rate could be enhanced by a factor of 11.5. Due to the developed functionality and the integrated GIS, periodic updating of the database in regular intervals (e.g. every three years) is greatly facilitated and will require much less effort than the first time data collection (the effort is expected to be in the order of several months). A special revisit function allows for quick and easy retrieval of parcel information for either quality control or to satisfy inquiries of property ownem about their billing statements (see Figure 5).
Positive Pmiect Exneriences At project start a first draft of the user’s manual built the basis for the definition of the user requirements. This lead to a clear understanding of the requirements from the customer’s point of view so that little changes to the requirements were necessary during later phases of the project. During the second half of the project the customer was involved in the database creation effort and during system testing. This not only improved the understanding of the system concept but also facilitated the technology transfer and shortened the training period after system installation at the customer site. In addition, it made the customer an active part of the project team, thus making it “his project”. The project resulted environment. For the approach bridges the development and the
in the implementation of a novel concept for combining GIS and film imagery in an operational first time the interactive use of fllm imagery in a digital image analysis environment was realized. This gap between data conversion (analog to digital) and actual data analysis by the operator. Finally, the delivery of the workstation could be completed on-time.
Negative Proiect Exuerlences
Sevcml development aspects were ‘ovcrqx~lfled’. These include the estimated time requkd to metlsupeWE pmwl, the expected gain due to computer assisted object boundary detection, and the integration of a voice input option. Originally, the time required to measure one parcel was estimated to be about two minutes. The time achieved during system acceptance was three minutes per parcel. This was mainly due to the fact that the performance of the selected platform (uVAX II) proved to be inadequate for the real-time execution of sophisticated image analysis algorithms, and the underestimated complexity of the task. The voice input device did not deliver the expected enhancements for user-system interaction. Due to time consuming training of voice patterns and frequent misinterpretations of voice commands no improvement in system throughput could be achieved. Consequently, the device remained unused during system operation. Incomplete documentation of the developed hardware component during the ma. -ttenance phase and follow-on contracts.
(i.e. computer controlled
zoom system) led to difficulties
The selection of the third party GIS proved to be unfortunate because the development of the system was discontinued in summer of 1989 due to unforeseen problems. Consequently, the GIS component had to be substituted. Arc/Info (ESRI) was chosen to replace KGB. This not only caused a limited redesign of the local database module, but also required a complete format conversion of the basemap. Finally, the effort to create the basemap was vastly underestimated. Especially the effort necessary for data clean-up and post editing to produce a consistent data set was much higher than expected.
CONCLUSION We have presented a project that was prompted by the need to establish an equitable basis for the calculation of a user’s fee to support the expansion and maintenance of the storm drain system of the City and County of Denver, Colorado. The developed system, PhotoStation, supports the extraction of impervious surface information on a parcel by parcel basis from aerial photography. Through the implementation of a novel system concept the integration of data acquisition from photography with data storage, administration, and analysis in a geographic information system is accomplished. Major experiences
. . .
derived from the chosen project approach include:
An attempt should be made to involve the user in all stages of the project (participatory design). Ideally, hands-on participation will make him the Yownern of the resulting product. An early agreement on stable user requirements is the best guarantor for an uninterrupted development phase. The creation of detailed documentation material is crucial for future system enhancements, and the maintenance and customer support phase.
Development of a Workstation Environment .
.
27
Careful selection of third party components (i.e. not only quality of the considered product but also market share and stability of producer) should minimize. the likelihood of future negative surprises. For applications involving the creation of a database the detailed definition of the requirements, analysis of available source documents, definition of the required data conversion effort, and specification of the best suited data model are critical.
ACKNOWLEDGEMENT This paper iS based on work performed at VWCEL Corporation (Boulder, Colorado, USA).
Review of~~to~‘c
Printed in Great
Pro~r~.~g
vol. 16, pp. 21-27,1992
Britain. All rights reserved
~4138~~15.~ 0 1992 PergamonPress Ltd
DEVELOPMENT OF A WORKSTATION ENV~ONMENT FOR THE ASSESSMENT OF A STO~WA~R DRAINAGE FEE E. H. Kienegger 2i TECH G&H, Schwanthakmtr. 143, D&W0 Munich 2, Germany
ABSTRACT The design and development of a workstation for the assessment of a stormwater drainage fee based on built-up surfaces is described. The work was performed under contract to the City and County of Denver, Colorado, USA. The requirement for such a system was prompted by the City’s decision to institute a fee for the expansion and m~nten~ce of the City’s sto~water drainage system. This fee should be based on the total mount of impervious surfaces (i.e. buildings, driveways, sidewalks) on the different properties. To determine the impervious areas on a parcel by parcel basis a method was selected that employs aerial photography in combination with existing property boundaries available on hand drawn assessor maps. Project requirements, setup and organization, and the implementation of the user requirements are briefly described. Subsequently, the strengths and weaknesses of the chosen approach are reviewed followed by a discussion of the experiences gained after more than three years of operation at the user’s site.
PROJECT HISTORY AND OVERVIEW Due to heavy development and expansion, the City and County of Denver was faced with mushrooming costs for the development and maintenance of a large sewer and wastewater system. To cover the expense of that development, the City introduced in 1980 a service charge to be paid by owners of properties that benefit from the wastewater system. The basis for determining the amount of the charge is the amount of built-up (impervious) area on a particular property. The higher the percentage of impervious area compared to the total area of the property the higher the service charge: A large con~butor to the water runoff problem would therefore make a higher contribution to the development and maintenance of the storm sewer system. A computerized billing system was implemented and a database generated based on existing assessor information about ownership and size of lots, and buildings on those lots. At the same time an effort was initiated to capture the impervious information per parcel more accurately since information about add-ons to existing buildings, driveways, or sidewalks was unavailable from existing records. The necessary measurements were performed manually by city inspectors. Soon the City became aware that the manual measuring method was not efficient enough to cover all parcels within the City in a reasonable amount of time. One inspector would perform four to five inspections per day, and four inspectors would capture the information of about 16 to 20 parcels per day. Considering the approximately 165,000 properties within the City of Denver, a rather formidable task was to be accomplished. Assuming 235 workdays per year, the information for about 4700 parcels could be obtained annually (assuming an average collection rate of 18 parcels per day), leading to a task that would consume approximately 40 years. Consequently, alternative methods were evaluated that would provide the necessary accuracy and accelerate the data gathering process by a factor of 10, thus reducing the time for completion to about three years. It was concluded that aerial photography would be the most versatile source of information for the task at hand. To support the capture of impervious areas baaed on aerial photographs, and to develop a strategy for ongoing database updating a project was started in March 1987 to develop a workstation that would provide the necessary functionality.
User Scenario The workstation to be developed had to support the following work scenario. An operator selects an aerial photogmph from a roll of p~~g~p~ mounted on the film scanning system. After registering the photog~ph to the film plane of the device
E. H. Kienegger
22
via its fiducial marks, s/he moves the CCD camera of the scanner under mouse control over the photograph to select a segment of the photograph at the desired resolution. The chosen segment is digitized and loaded into the memory of an image processing subsystem. In a next step the corresponding vector information is extracted from the geographic database and overlaid onto the image. Discrepancies between image and vector data can be removed by identifying additional tie points located on corresponding features in image and vector overlay. Supported by the overlaid vector information, in this case property boundaries, the user outlines and labels impervious areas such as buildings, driveways, and sidewalks. Once the data collection for the segment is completed the user either selects a new segment, moves on to another photograph, or quits the session. Using this approach the impervious surface information for the City can be captured photograph by photograph.
Develonment
Tasks
For the realization of these requirements
the development
of the workstation was divided into the following tasks:
Software modules . photogrammetric module for registering photographs to the database; . graphic editor to support the acquisition of vector data from raster images; . algorithms for the computer assisted detection of object boundaries in digital imagery; . user interface and message handling; . device drivers (e.g. digitizing board, voice recognition device, film scanner); . interface to third party Geographic Information System (GIS) and Relational Database Management System (RDBMS). Hardware . development of a computer controlled optical zoom system consisting and zoom lens for the digitization of segments of aerial photography; . integration of the workstation components.
of a CCD area array camera
Data . . . . . .
conversion of the existing assessor maps into digital form (vector data); creation of a seamless data set in a standard map coordinate system; transfer of the information into a third party GIS database; production of a set of B/W aerial photographs; organization of photographs into continuous flight lines covering the entire area of the City; control point selection for registering the photographs to the basemap.
Coverage for entire
Geographic Database (spatial and attribute data)
Film Scanning
system
Local Database
Joystick control
USU
Coverage for image segment (
Mouse
Modified coverage for image segment
coverage for image segment Fig. 1.
Overview of data flow and software modules
Develcpmeotof a ~~~~on
E~v~onment
23
The interaction of the different software modules is illustrated in Figure 1. Once a particular photograph has been selected
and registered to the film plaue of the scanner, the vector data corresponding to the photograph are downloaded to the local database for improved data access. Now the user selects a segment of the photograph using a joystick to control the position and resolution of the CCD camera. After digitizing the selected image segment, the corresponding vector data is retrieved from the local database and overlaid onto the image. During the overlay operation the vector data are distorted to match the geometry of the image data. Thls transformation is based on a previously performed exterior orlentation that registers the photograph to the basemap. The registration process is performed during a preprocessing phase where all ~o~gmp~ are registered to the basemap based on control point information. Remaining mismatches between image and vector data can be removed through additional tie points establishing a local transformation. In the next step the user identifies a parcel to be worked on and outliies and labels impervious surfaces using mouse and digitizing pad. After the ifiormation of all parcels within the chosen segment have been captured, the user moves on to a new segment of the photograph. Using this approach the data of the entlre photograph can be extracted. Whenever the user selects a new photograph or quits the current session, the newly collected data are transferred from the local database back to the geographic database of the third party GIS. For the ~plern~~~on of the required functionality, the hardware envi~~ent depicted in Figure 2 was chosen. The various hatdware perlpherals are grouped around a Dee MictoVax II. Interactive film scanning is provided by a me~~tion light table and a computer controlled optical zoom system with integrated CCD area array camera. The anaIog video signal output by the CCD camera is transferred to a Gould FD5000 image processing system capable of digitizing the incoming signal in real-time and storing it in its internal image memory. The digital image is displayed on a separate image monitor. The user interacts with the system via Video Display Tetminal (VDT), digitizing board, joystick, and an optional voice input device. A video printer is connected to the image monitor for instant color hatdcopies. The hardware interface to the billing system hosted on an IBM mainframe is realized through a data conversion device. With the exception of the optical zoom system off-the-shelf components could be used.
I
Storage subsystem (Tape, Optical disk)
I s
1
Interface to IBM mainframe
I
1
CCD array camera with computer controlled zoom lens
Pig. 2.
Hardware environment of Photostation
In addition to the software and hardware environment, the initial set of data required for system operation has to be provided. Thus the 420 assessor maps coveting the Clty of Denver had to be converted into a digital basemap. For this purpose they were manually digitized by a subcontractor. Subsequently, the individual data files (one per map sheet) had to be transformed into a standard map coordinate system and edge-matched to obtain a seamless data set. Approximately 1200 aerial p~~gm~ at a scale of 1:3,600 were produced by a second su~on~ctor. In a preprocessing step the p~~gmp~ were organ&d into flight lines running North-South and registered to the basemap by identifying ground conttol points on common features in photographs and basemap.
Qrganlzation of Develonment Tasks The project tasks required to implement the described functionality wefe divided into a number of work packages @VP)and dlstrlbuted between the member of the development team. The work packages and the cozening man power to perform
E. H. Kienegger
24 the work are listed in Table 1.
The work packages were distributed between six software and two hardware (i.e. one electrical and one mechanical) engineers. Total development time was about five person-years excluding WP9 and WP11. The creation of the basemap and the registration of the photographs to the database required more than three person-years.
Table 1. Workpackages
and required man power
Resources
Tasks
WP
Development of the user interface, message handling, and device driver software Development of local database Development of the photogrammetric software, geometric transformations and data acquisition tools Design and implementation of algorithms for the computer assisted object boundary detection Development of the computer controlled optical zoom system Development of driver software for zoom system Implementation of link to IBM hosted billing database Manual digitization of existing assessor maps Creation of the digital basemap based on digitized map data Production of aerial photography Registration of photography to basemap
1 2 3 4 5 6 7 8 9 10 11
MM . man months;
Table 2.
12 MM by 1 Eng. 6 MM by 2 Eng. 16 MM by 1 Eng. 12 MM by 2 Eng. 8 MM by 2 Eng. 2 MM by 1 Eng. 2 MM by 1 Eng. subcontracted 36 MM by several Tech. subcontracted 2 MM by 1 Tech.
Eng. . . . Engineer;
Tech. . . . Technician
Summary of project related data
March 1987 May 1988 Aug. 1988
Project start System delivery Acceptance Test Resources SW&HW development Database creation
5 person years 3 pctson years
Development environment Platform Operating system Programming language
Dee uVAX II VAXIVMS Pascal
Project management Tool Cost, task, problem tracking Reporting
MicroPlanner (Apple MacII) weekly project meetings monthly progress reports
Third Patty components RDBMS GIS
Oracle (Oracle Corp.) KGIS (Kork Systems)
Subcontracts: Manual digitizing of Assessor maps Aerial Photography
Development
Environment
and Project Management
The development environment was provided by the VAX/VMS operating system. No software development tools other than debugger and text editor were used. The software system was implemented using the PASCAL programming language. A
Development
of a Workstation
Environment
25
summary of the project data is provided in Table 2. Project planning, task estimation, task tracking, and progress reporting was supported by a project management tool (MicroPlanner on an Apple MacII). Weekly project meetings were held to discuss problems, check progress, and adjust the project plan if necessary. Monthly progress reports were sent to the customer to report on project status.
PROJECT RESULTS
AND EXPERIENCES
The development effort resulted in the system PhotoStation shown in Figure 3. Figure 4 illustrates the field of view of the zoom system in overview mode with superimposed parcel boundaries. An example of a completed parcel retrieved from the database using the revisit function of the system is shown in Figure 5.
Fig. 3.
Fig. 4.
Original implementation
of PhotoStation
Segment of aerial photograph in overview mode with overlaid property boundaries
Fig. 5.
Segment of photograph showing measured parcel and impervious areas
E. H. Kienegger
26
The data collection rate achieved by the users operating the system averaged about 100 parcels per day. After adding a second workstation in March 1989 the collection rate doubled to about 220 parcels per day. This lead to the completion of the first time data collection in January of 1992. When compared with the originally used manual field measurements, the data collection rate could be enhanced by a factor of 11.5. Due to the developed functionality and the integrated GIS, periodic updating of the database in regular intervals (e.g. every three years) is greatly facilitated and will require much less effort than the first time data collection (the effort is expected to be in the order of several months). A special revisit function allows for quick and easy retrieval of parcel information for either quality control or to satisfy inquiries of property ownem about their billing statements (see Figure 5).
Positive Pmiect Exneriences At project start a first draft of the user’s manual built the basis for the definition of the user requirements. This lead to a clear understanding of the requirements from the customer’s point of view so that little changes to the requirements were necessary during later phases of the project. During the second half of the project the customer was involved in the database creation effort and during system testing. This not only improved the understanding of the system concept but also facilitated the technology transfer and shortened the training period after system installation at the customer site. In addition, it made the customer an active part of the project team, thus making it “his project”. The project resulted environment. For the approach bridges the development and the
in the implementation of a novel concept for combining GIS and film imagery in an operational first time the interactive use of fllm imagery in a digital image analysis environment was realized. This gap between data conversion (analog to digital) and actual data analysis by the operator. Finally, the delivery of the workstation could be completed on-time.
Negative Proiect Exuerlences
Sevcml development aspects were ‘ovcrqx~lfled’. These include the estimated time requkd to metlsupeWE pmwl, the expected gain due to computer assisted object boundary detection, and the integration of a voice input option. Originally, the time required to measure one parcel was estimated to be about two minutes. The time achieved during system acceptance was three minutes per parcel. This was mainly due to the fact that the performance of the selected platform (uVAX II) proved to be inadequate for the real-time execution of sophisticated image analysis algorithms, and the underestimated complexity of the task. The voice input device did not deliver the expected enhancements for user-system interaction. Due to time consuming training of voice patterns and frequent misinterpretations of voice commands no improvement in system throughput could be achieved. Consequently, the device remained unused during system operation. Incomplete documentation of the developed hardware component during the ma. -ttenance phase and follow-on contracts.
(i.e. computer controlled
zoom system) led to difficulties
The selection of the third party GIS proved to be unfortunate because the development of the system was discontinued in summer of 1989 due to unforeseen problems. Consequently, the GIS component had to be substituted. Arc/Info (ESRI) was chosen to replace KGB. This not only caused a limited redesign of the local database module, but also required a complete format conversion of the basemap. Finally, the effort to create the basemap was vastly underestimated. Especially the effort necessary for data clean-up and post editing to produce a consistent data set was much higher than expected.
CONCLUSION We have presented a project that was prompted by the need to establish an equitable basis for the calculation of a user’s fee to support the expansion and maintenance of the storm drain system of the City and County of Denver, Colorado. The developed system, PhotoStation, supports the extraction of impervious surface information on a parcel by parcel basis from aerial photography. Through the implementation of a novel system concept the integration of data acquisition from photography with data storage, administration, and analysis in a geographic information system is accomplished. Major experiences
. . .
derived from the chosen project approach include:
An attempt should be made to involve the user in all stages of the project (participatory design). Ideally, hands-on participation will make him the Yownern of the resulting product. An early agreement on stable user requirements is the best guarantor for an uninterrupted development phase. The creation of detailed documentation material is crucial for future system enhancements, and the maintenance and customer support phase.
Development of a Workstation Environment .
.
27
Careful selection of third party components (i.e. not only quality of the considered product but also market share and stability of producer) should minimize. the likelihood of future negative surprises. For applications involving the creation of a database the detailed definition of the requirements, analysis of available source documents, definition of the required data conversion effort, and specification of the best suited data model are critical.
ACKNOWLEDGEMENT This paper iS based on work performed at VWCEL Corporation (Boulder, Colorado, USA).