Final Report for the Niagara Peninsula Conservation Authority 2010 Update to 1m Contour Supporting Digital Terrain Model for Niagara Watershed

Transcription

1 Final Report for the Niagara Peninsula Conservation Authority 2010 Update to 1m Contour Supporting Digital Terrain Model for Niagara Watershed Date: April 9, 2013

2 TABLE OF CONTENTS 1. PROJECT BACKGROUND METHODOLOGY SOURCE MATERIALS DTM UPDATES SITE SPECIFIC NOTES QUALITY CONTROL QUALITY MANAGEMENT APPROACH PROJECT SPECIFIC QUALITY CONTROL DELIVERY ACCURACY ASSESSMENT... 8

3 1. PROJECT BACKGROUND In 2002 First Base Solutions was the successful vendor on a project to acquire aerial photography and supply digital orthophotography and digital terrain data across the GTA plus expanded coverage of Niagara, Hamilton and several counties/municipalities surrounding the GTA. The goal was to have a consistent and accurate digital orthophoto base and accurate, structured, elevation data. We acquired 1:10,000 scale colour aerial photography which we then scanned to yield a 20cm ground pixel resolution. The photography was controlled with the acquisition of onboard AGPS/IMU data for every image plus ground photo control and an aerial triangulation adjustment was completed. The digital terrain data was built to support the orthorectification process plus pre-engineering survey and design and floodplain-mapping programs with the production of detailed topographic mapping at a minimum scale of 1:2,000 with a contour interval of no less than 1.0 metre. The compiled elevation data was composed of points and breaklines. Breaklines were compiled and coded for the following ground surface features: Hydrology Themes: Transportation Themes: Miscellaneous Features: Major Ditch centrelines Marsh/Swamp outlines Stream centrelines Shorelines and major rivers Water Bodies Large Dams (tops and bottoms) Bridge Decks Significant Driveways / Accessways Railroad centreline Road Edge: paved, gravel and curbed Large Headwalls Large Retaining Walls In addition, miscellaneous breaklines were compiled along all: Gullies Ridge breaks Top and base of significant piles Top and bottom of bridges, overpasses and ramps Top and bottom of quarry / cliff edges Tops and bottoms of slopes Point data was collected on a 40-metre grid density, further densified by the generation of a 10m grid, with specific elevations collected for summits of hills and bottom points of depressions. Based on the nature of the terrain, thee various 3D features were sufficient to control the orthogonal rectification of the aerial photography and generate a DTM to support municipal mapping purposes with 1.0m contour generation. Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 1

4 In 2006 we acquired 10cm digital colour aerial photography of the Region of Niagara. The photography was controlled with the acquisition of onboard AGPS/IMU data for every image plus ground photo control and an aerial triangulation adjustment was completed. We then completed an update of the existing 2002 DTM to ensure that in areas of significant change the DTM was updated to reflect these changes. The newly compiled DTM was compiled to the same accuracy standard and coding structure as the 2002 DTM. In 2007 and 2010 the existing 2002 DTM in the City of Hamilton was updated to reflect the current conditions for each Update Year. This current 2010 Hamilton DTM has been updated to the same accuracy standards as the 2002 DTM, accurate to +/- 0.50m. 1.0m Contours were never provided as a deliverable in any of the projects listed above. 2. METHODOLOGY The purpose of this project was to utilize the existing Year cm SWOOP stereo models to complete a full check and update of the existing DTM to ensure that it was suitable to produce a 1.0m Contour at the 90% confidence level. We focussed on surface water features and their associated morphology. The entire project area, including all buffered tiles, resulted in a total project area of 2884km2. The existing data currency, which was checked and updated, is shown below: 2.1 SOURCE MATERIALS The data used for this project consisted of the imagery flown for the Ministry of Natural Resources under their SWOOP010 project. First Base Solutions was not contracted to MNR to complete the SWOOP 2010 project. In order to complete the DTM check and updates from the 2010 imagery, to satisfy the Niagara Conservation Authority Contour project, we were supplied with the following datasets: Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 2

5 2010 raw images in TIF format Exterior orientation data resulting from SWOOP 2010 aerial triangulation adjustment DTM data from 2002, 2006 or 2010 The SWOOP 2010 Niagara image set consisted of 5755 adjusted digital colour images acquired to support a horizontal and vertical vector data accuracy of 0.5m and a final pixel resolution of 0.2m for all data collected at a confidence interval of 90%. Digital colour images were flown at a mean scale of 18,234 and mean GSD of 16 cm using Vexcel UCD and UCXp digital cameras outfitted with airborne GPS and inertial measuring units. The ground control data, used in the aerial triangulations adjustment that was completed, consisted of 31 new Horizontal and Vertical (H&V) control points and 10 new H&V points used as checks. All of the control data was collected in UTM Zone 17 NAD83CSRS and the CGVD28 vertical datum. No data was transferred or measured from existing imagery or previous mapping data in order to generate a control point. 2.2 DTM UPDATES The first task in completing the project was to reproject the existing DTM datasets from the current datum/projection of UTM NAD 83 original to UTM NAD 83 CSRS. To accomplish this, the existing DTM was converted to Microstation V8i format. Once this was done the files were then converted using Bently Powerdraft which utilizes a conversion table to re-project the files in a batch process to UTM NAD 83 CSRS. Once the DTM files were re-projected to UTM NAD 83 CSRS the task of checking and updating the existing DTM began. To complete this First Base Solutions set the existing Year cm SWOOP stereo models using the Exterior Orientation parameters, Camera Calibration information and Raw Imagery as supplied by NPCA. First Base Solutions assumed that the existing stereo models were properly adjusted and that no further enhancements or control was required. All DTM updates were completed in one our DAT-EM 3d Softcopy workstations. Each workstation is equipped with dual monitors along with hand and foot pedals for movement of the map cursor. The first monitor displays the 3d Stereo Imagery while the second monitor contains editing toolbars as well as a project specific sidebar menu that contains all of the various vector mapping features specific to this project. Each feature is linked to a database that contains the unique Level, Weight, Colour and Linestyle of each feature. All Mapping was completed in the Microstation v8 platform. The actual task of updating the existing DTM to 2010 conditions required a model by model pan and check of the existing DTM superimposed within the 2010 Stereo Models. Each model was visually inspected by an experienced Mapping Technician. The Mapping Technician focussed on obvious changes in the magnitude of +/- 0.50m or greater that had occurred between when the DTM was last compiled/updated and the current conditions as reflected in the 2010 photography. These changes include new subdivisions, road widenings, Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 3

6 changes caused by erosion, changes to drainage patterns and locations, pits/piles, just to name a few. As we advised in our response to the RFP, the existing DTM, when viewed within the new 2010 Stereo Models, could show differences of +/- 1m. The different adjustments from the different datasets/years of photo that have been utilized in the past will exhibit possible allowable differences of +/- 50cm. From past experience, we are aware that this can and does occur in instances where the two different datasets are residing at the outside threshold, or polar opposite, of their allowable accuracies. For example, the top of a culvert in the existing DTM may measure an elevation of 278m while this very same unchanged culvert, when viewed in the new 2010 stereo models, may actually measure an elevation of 279m, when in actual fact the real elevation is in or around 278.5m. Based on the allowable accuracy tolerance of +/- 50cm of both datasets, neither dataset can be deemed incorrect. As a result, since no obvious or actual change has occurred, an update or edit to the existing DTM was not completed in these types of situations. Please be aware that all new compilation, where applicable, will be within +/- 0.50m of its true location as per the adjusted 2010 Stereo Models supplied. As changes to the DTM were identified, the Mapping Technician either removed or edited the existing linework. New linework was compiled to reflect the current conditions. The layer coding used for this project was consistent with the 2002 layering. This generally included Water Bodies, Linear Hydrologic Features, Road Features, Overpasses and Bridges and significant Ditches and other constructed features, Obscured Areas, General Breaklines and Mass Points and 1.0m Contours. In addition to ensuring the features described above were properly accounted for, the Mapping Technician also generated a TIN and 1.0m Contours on the fly. This enabled the compiler to ensure the resulting DTM produced a 1.0m Contour that properly formed the ground at the 90% confidence level. As the DTM was edited and modified the Mapping Technician, with just the click of a button, instantly generated a TIN and 1.0m Contours to ensure the changes to the DTM properly describe the 2010 conditions. It was our understanding that 1.0m Contours existed that had been generated on the original 2002 DTM. Due to the fact that past updates to the DTM, which occurred in 2006, 2007 and 2010, did not include updates to the 2002 Contours, we generated a brand new m Contour. By generating new contours rather than updating very old contours, the result is a much more accurate contour product. 2.3 SITE SPECIFIC NOTES We did not encounter any unique or unusual scenarios during our update process. Updates were typical of what is normally found and included such things as new residential subdivisions, road widenings, changes in drainage patterns etc. Many wooded areas that were difficult to see through in 2002 were more visible in the 2010 imagery resulting in new compilation within these areas. Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 4

7 2.4 QUALITY CONTROL QUALITY MANAGEMENT APPROACH This section illustrates our processes for quality planning, assurance and control and the tools and techniques we employ to support these processes. Our team was charged with organizing and managing this project to provide quality solutions. A Programme and Project Management (PPM) methodology constitutes our approach for managing the project. PPM contains a route map of the successful tasks to effectively manage our projects and includes QMP checkpoints throughout the projects to ensure the quality of products and that the client accepts and is satisfied with the work. The QMP focuses on successfully meeting 7 quality indicators: Scope Management agreement on and maintenance of the boundaries of the project and a realistic approach for managing scope, scope change and managing expectations. Team & Infrastructure the resourcing and mix of skills/experience is appropriate, the roles and responsibilities are well defined and team integration is effective. In addition, the technical environment (both systems and workplace) and basic tools required to succeed are in place. Delivery and Acceptance the project plans, schedule and budgets are reasonable; progress reporting and communication of issues and decisions are acceptable. Program and project leadership is effective. In addition, there is agreement on both the criteria and process of accepting work products as complete. Stakeholders the Internal and External stakeholders are supportive, committed and involved. Key groups become engaged through improved awareness and understanding of the work required to achieve the program s objectives. Benefits the business rationale and various benefits anticipated from the program are known, realistic and achievable. The program is focused on achieving the goals and results. Risk Management the risks are tracked, understood and managed. Mitigation actions are addressed and project leadership is informed of progress in the risk management activities. Delivery Organization Benefits establishing, agreeing, and monitoring the provision of benefits accruing from the project, (for example - knowledge transfer and skills development) and maintaining and protecting interests in relation to the project PROJECT SPECIFIC QUALITY CONTROL Our Softcopy technology provides an initial quality control in the Stereo Model setup process. The absolute orientation parameter matrix (Kappa, Phi & Omega) along with the perspective center co-ordinates provided to us were stored as a bundle file attached to each image. Compilers select the two adjacent images that form the model to be mapped and the model set is already complete. The advantages of the Softcopy environment are quite obvious when the task of revision and updating of an existing vector base are required. Not only are the changes to the DTM and Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 5

8 Vectors instantly apparent in a softcopy environment but also changes in surface elevation affecting the subsequent contour depiction. The softcopy environment is in itself the ultimate Quality Control tool for recognition of incorrect Z attribute information. Existing vector data with incorrect elevation attributes would not occupy the correct position in a 3D space relative to the digital stereo image display. Revision of an existing vector/elevation data set using a softcopy approach provides the facility to not only update features that have changed in X,Y location (i.e. roads widened, sidewalks added etc.) but also update elevations to features that have not changed in X,Y location but have changed in Z value. (i.e. second story building additions) or features that may have incorrect elevations attached (zero Z values caused by spikes or process manipulation). The Softcopy environment is the perfect QC tool. Simply put, the compiled vector or point data and stereo image occupy the same physical model space. This superimposition ability takes all the guesswork out of the compilation and editing process. A full topology check was run on the DTM using our MAPS-3D topology tools. This routine checks for duplicate lines and points, overshoots, undershoots etc. We check that all mapping is compiled on layers with a _2012 tag to indicate new compilation. First Base Solutions completed a final model by model sweep of all DTM tiles, checking that all areas of change were identified and fixed. We confirmed that the data produces accurate 1m contours, with emphasis on accurate drainage patterns (i.e. changes in elevation and erosion / course change). Once the DTM was checked and confirmed we generated 1.0m contours. Our contour checks included the following: 1m Contours 1m and INDEX 5m Level structure. Contours should be delivered in the same 3km tile structure as the DEM. All Contours tiles must be tied to adjacent tiles to create a seamless contour product. All contours must cross transportation correctly and there should be no isolations and the contours should cross roads evenly unless rounding curves, All contours must show the direction of flow unless the ground is flat. There should be no isolation contours on the drainage features unless the drainage feature is a ditch is no obvious flow direction (standing water). Contours should not touch closed shoreline features (ponds / lakes). Removal of all isolation contours smaller than 6 square meters. Contour should never cross. Our final process is to perform a visual sweep of the contours to ensure the contours look visually appealing. We look for oddly shape contours indicating erroneous xy spikes. 3. DELIVERY All final delivered data is metric and in UTM Zone 17, NAD83 CSRS. Feature coding remained consistent with the original 2002 deliverables as follows: Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 6

9 ACCESS WAY - UNSPECIFIED BREAK LINE - PT2PT BRIDGE CULVERT TO SCALE DAM - TO SCALE DEM POINTS DITCH - CENTRELINE PILE RACETRACK - EDGE RAIL LINE - ABANDONED RAIL LINE - CENTRELINE RETAINING WALL RIVER-STREAM RIVER-STREAM INDEF ROAD CURBED ROAD EDGE - UNDER CONSTRUCTION ROAD GRAVEL ROAD PAVED SHORELINE SHORELINE INDEF SWAMP WATER BODY Digital files are in AutoCAD format and contain points, breaklines and 1.0m contours. A 10m grid of points is included and we ve layered the points to indicate those points actually compiled separate from those that were auto-generated. Final layering in the AutoCAD files maintained the same naming convention as the original 2002 files outlined above. Layers that contained modified or newly compiled features were assigned a _2012 suffix. The layers must be viewed simultaneously to reflect the complete feature. When we noticed an area of change, the features were removed from the existing layer and compiled from the new photography in the _2012 layer. For example, to view all ROAD-CURBED features the layers ROAD-CURBED and ROAD-CURBED_2012 need to be visible. In addition, the following layers were completely new in 2012: CONTOUR INTER 1M CONTOUR INDEX 5M CONTOUR INDEX TEXT DEM POINTS - GENERATED OBSCURED AREA - POLY Data delivery was in 3km x 3km tiles with a file naming convention based on the lower left coordinate value as follows: Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 7

10 648_47820_3K_DTM_FBS_2012.dgn 4. ACCURACY ASSESSMENT Imagery collected at a 16cm pixel resolution that is then adjusted using both AGPS/IMU collected data plus field photo control can support mapping accuracies of ± 50cm at the 90% confidence level. Although we did not acquire the imagery or acquire the field photo control or complete the aerial triangulation adjustment, the reports submitted with project returns indicate the SWOOP 2010 imagery will support this accuracy level. The influence of a set of variables on the measuring precision in XY and in Z has been found to include the following: the distribution/location of points in the model the photogrammetric operators and their experience the type of points These factors are in addition to the accuracy of the photogrammetric mapping software, the geometric accuracy of the image, the camera and calibration, density and accuracy of the ground control and the results of the aerial triangulation adjustment. When compiling DTM data the operator works within the stereo model and carefully defines all changes in elevation with breaklines. Following this a grid of points fills in the remaining terrain. It is generally accepted that the minimum mapping experience to achieve significant results has been considered to be one year. Our mapping technologists have been doing this type of mapping on average for 38 years and have been with First Base Solutions for over 10 years. This experience is essential to building an accurate elevation dataset, particularly since much of the focus of this project was along drainage and water features where it can be difficult to define the ground. The type of points being compiled will have varying accuracies associated with them. Obviously, points on hard surfaces are much easier to resolve in stereo and measure most accurately. Within densely wooded areas the mapping operator will look for openings where the ground is visible in order to compile elevation points. Since the imagery was flown in the spring there is little vegetation that interferes with the compilation process. Generally we confidently quote achievable horizontal accuracies of 1.5 times the pixel size and vertical accuracies of 2 times the pixel size. Measurements of clearly defined features on hard surfaces will be better than that but this represents the overall accuracy of most sites. For this particular project since the image was acquired at a 16cm pixel size it is possible to compile measurements horizontally accurate to ±24cm and vertically accurate to ±32cm. This is more than adequate to generate DEM data to support 1.0m contours. Within each site we completed control checks using ground photo control acquired for the Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 8

11 SWOOP project. The Technical Reports reported on the ground photo control points checked and included a description, the coordinates supplied to us and the residuals following our measurements of these points. Our overall LMAS is The SWOOP2010 project requirements were for an LMAS of 0.500, confirming our measurements more than meet the Niagara Watershed project requirements. First Base Solutions confirms that the DTM and contour data delivered comply with the project specifications and accuracy requirements. First Base Solutions confirms that the DTM and 1.0m contour data delivered have been produced according to procedures that have been demonstrated to produce data with particular horizontal and vertical accuracy values as: Compiled to meet ±0.5m (meter) horizontal accuracy at 90% confidence level ±0.5m (meter) vertical accuracy at 90% confidence level Ann-Marie Mailhot-Aron, B.Sc., O.L.S., O.L.I.P. First Base Solutions Date Final Report Update to 1 Metre Contour Supporting DTM for Niagara Watershed Page 9