Loading...
HomeMy WebLinkAboutN- 7 Orthophoto Base Mapping proposal Page 1 of 4 City of Azusa Base Mapping Proposal General Walker Associates is pleased to provide the following proposal for aerial photography and photogrammetric mapping services to the City of Azusa. The following paragraphs of this document summarize the project design and deliverable items. Project Boundary The attached graphic outlines the project limits. Three areas are identified on the graphic, namely are blue, yellow and orange. This project shall include the generation of the defined mapping datasets over all three of these areas. The list below summarizes the required data items: 1. 1”=600’ scale color aerial photography shall be collected over the entire project area. 2. 2-foot contour data shall be generated over the entire project area. 3. 1”=100’ scale planimetric data shall be generated over the entire project area. 4. 1”=100’ scale color digital orthophotography with 0.5 foot ground resolution shall be generated over the entire project area. Aerial Photography Walker Associates will acquire 1”=600’ color aerial photography over the project area. The attached flight map indicates the project boundary and the planned photo acquisition plan. To assure the highest quality aerial photography is acquired, Walker Associates will utilize the services of Global Remote Sensing of Riverside, California. Global Remote Sensing operates a LH Systems RC-30 aerial camera with a 101 AWAR resolution. This aerial camera system is one of the most advanced systems available today. The calibration report on the camera from the USGS is included as an attachment to this document. In addition to the basic color aerial photography, airborne GPS exposure station control will be acquired with each photograph. This airborne GPS control enables the project to be completed more efficiently and with a higher degree of accuracy. To assure that the desired project area is acquired with the aerial photography, the final flight map will be sent to the City for review prior to the actual flight. Ground Control Ground control for this mapping project will consist of 12 points evenly distributed over the project area. The attached control graphic presents their general locations. The points will consist of pre-flight targets and post-flight photo identifiable locations. The Page 2 of 4 ground control survey for this project will be performed by Mr. William Meager, Licensed Surveyor # 5948, of WM Holdings Incorporated located in Ventura, California. Contact Prints Walker Associates will provide the City of Azusa with one set of 9” x 9” color contact prints of all the acquired aerial photography. These prints will be delivered within three weeks after the acquisition of the aerial photography. Image Scanning The aerial film will be scanned on our LH-Systems DSW-500 precision photogrammetric scanner. The original negative film will be scanned. To provide for digital imagery at the desired resolution the film will be scanned at 14 microns. This will produce digital imagery with a ground resolution of 0.3 feet. This is the resolution of the internal digital imagery that will be used for triangulation, mapping and digital orthophoto production. It will be resampled in the final processing of the digital orthophotos to generate the output 0.5 foot resolution product. Aerial Triangulation The digital imagery will be triangulated utilizing the LH-Systems Socet Set digital photogrammetric workstations within Walker Associates. Within the process precise measurements will be made on all the digital aerial images. These precision measurements will be processed through a fully analytical aerial triangulation adjustment program to generate the final results. The final adjustment of the aerial photography to the control will be accurate enough to support the mapping of 1”=100’ scale planimetric features and 2-foot contours to National Map Accuracy Standards. Stereo Mapping The compilation of the planimetric features and elevation data for 2-foot contours will be performed in the digital mapping environment within Walker Associates. KLT Atlas digital mapping systems will be used. All mapping data for this project will be compiled from stereoscopic imagery. The list of planimetric features that will be compiled is included as an attachment to this document. The compilation process for 2-foot contours consists of the collection of individual elevation points named mass points and connected elevation values named breaklines. Mass points are discrete elevations values collected on an even grid pattern of every 100 feet on the ground. Breaklines are collected along points of inflection or changes in elevation on the ground. They are collected at the edge of roads, top and bottom of ditches and along ridgelines for example. Data Edit Page 3 of 4 The planimetric and digital terrain elevation data will be exported from the extraction equipment to the digital editors for final review. The editors will merge the data into a continuous dataset covering the entire project area. From this format, individual sheets will be cut on the approved tiling scheme. For 1”=100’ scale mapping a nominal sheet size of 2500 feet on a side is usually selected. The digital elevation data will be utilized to generate a TIN surface in the terrain modeling software. Form the TIN the 2-foot contours will be generated. The editors will then visually inspect and edit the contours for completeness and cartographic appearance. As a final QC step a paper plot will be generated for each sheet and reviewed. The planimetric data will be review in a similar manner by the editors. Here the review process focuses more on the completeness of the compilation process and the correct attribution of all features. Once a sheet of contour and planimetric data passes the final QC process, it will be translated from AutoCAD to ArcView shape file format. The final digital files will be delivered to the City on CD-ROM. Orthophoto Generation The digital elevation data that was compiled for the generation of the contour data and the digital imagery will be utilized to generate the digital orthophotos. The LH-Systems Orthophoto generation software will be used for this process. The digital processing of the imagery will remove distortions caused by relief displacements in the data and generate a continuous digital image over the entire project area. For consistency, the digital orthophotos will be tiled in the same manner as the planimetric and 2-foot contour data. The final deliverable items will be TIFF files with a TIFF world file delivered on CD-ROM to the City. Product Accuracy All the mapping data and products that will be generated for the City of Azusa under this project will meet the National Map Accuracy Standards for the defined scale of data. Specifically, the 1”=100’ planimetric data and the digital orthophoto data will have a horizontal accuracy of ≤ 1.5 feet at the one standard error level in X and Y. The 2-foot contour data will have a vertical accuracy of ≤ 0.61 feet at the one standard error level. Spot elevations will be accurate to ≤ 0.3 feet at the one standard error level. Deliverable Items 1. Flight maps 2. One set of color 9”x9” contact prints 3. A control survey report 4. An aerial triangulation report 5. 2-foot contour sheets in digital format as AutoCAD and ArcView shape files (preliminary plan indicates 100 2500’ x 2500’ tiles). 6. Planimetric data as sheets in digital format as AutoCAD and ArcView shape files (preliminary plan indicates 100 2500’ x 2500’ tiles). Page 4 of 4 7. 0.5 foot resolution color digital orthophotos in digital format as TIFF files with TIFF world files (preliminary plan indicates 100 2500’ x 2500’ tiles). Project Costs The total cost to perform all the services for this project are $ 149,600. Project Schedule The preliminary project schedule is attached. As you will notice it is contingent on the date of acquisition of the aerial photography.