Iowa Department of Transportation Office of Design. Photogrammetric Mapping Specifications

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1 Iowa Department of Transportation Office of Design Photogrammetric Mapping Specifications March Purpose of Manual These Specifications for Photogrammetric Mapping define the standards and general procedures to be followed in the preparation for and compilation of large scale engineering mapping used in the development of highway improvement projects at the Iowa Department of Transportation (IDOT). These specifications include details for Photo Control Layout, Aerial Triangulation, Plan and Digital Terrain Model Mapping and Ortho rectified imagery. These specifications are intended to comply with Chapter 20A 3, Plan Development CADD Standards, of the IDOT Design Manual. 2 Project Overview The project description and a mapping boundary in MicroStation or Google KMZ format will be provided by IDOT. A four digit Survey and Photogrammetry (SAP) number will be provided for each project. This unique number is used in naming the working files during the survey and photogrammetry processes (see Design Manual Chapter 40, Section D 1). Digital mapping camera (DMC) images will be provided by the IDOT for subsequent photogrammetric operations. For photo control layout, the consultant is responsible for determining and specifying the locations, spacing and configuration of photo control points to meet the mapping accuracy standards set out in these specifications for the entire mapping boundary. The photo control layout shall be provided to the IDOT for field collection and the coordinates will be provided to the consultant after field activities are complete. Aerial triangulation will include the use of airborne global positioning system and inertial navigation system (ABGPS/INS). This data will be acquired during the flight mission and processed by the aerial photography vendor and willl be provided by IDOT. A fully analytical aerial triangulation solution shall be performed to georeference the spatial models to the ground. Digital stereo compilation of plan features and terrain data is required within the entire mapping boundary. A MicroStation file with the preliminary field survey data will be provided by IDOT and the stereo compilation shall supplement data collected in the field. A GEOPAK triangulated irregular network (TIN) of the terrain is required. An orthorectified image of all strips of images provided is required. 3 Datum, Coordinate Systems and Units Coordinate system definitions for each project will be provided by the IDOT Office of Design using these general guidelines: 1

2 Vertical positions shall be referenced to the North American Vertical Datum of 1988 (NAVD88) using the Geoid Model GEOID12a, unless noted otherwise. Horizontal positions shall be referenced to NAD83(2011) Iowa State Plane North (zone 1401) or Iowa State Plane South (Zone 1402) using a combined scale factor and point to scale about for providing a grid to ground transformation OR Iowa Regional Coordinate System (IaRCS) Zones 1 through 14 (IaRCS information: Units of measurement shall be U.S. Survey feet. The U.S. Survey foot is defined as 1 meter=39.37 inches. 4 Project and Photo Control Preliminary survey required to execute project and photo control will be provided by the IDOT in accordance with the procedures and accuracies specified by the IDOT. Photo control coordinates will be provided in ASCII format and include point number, easting, northing, elevation and point description. Photo control coordinates are established relative to the project control. 5 Aerial Photo Control Layout Field surveyed photo control points are necessary to orient and position the imagery relative to the ground. The photo control configuration should surround the project mapping boundary and have adequate spacing such that when supplemented with pass and tie points, the aerial triangulation accuracies identified in Section 6 are achieved. Photo control can be classified as preflight targets or photo identifiable control points selected after the aerial flight is completed. Accessibility for surveying should be considered when selecting locations for control points. 5.1 Preflight targets When a project includes preflight targets, target coordinates and the target layout will be provided by the IDOT. Targets are established to comply with IDOT Specifications for Targeting Ground Control Points for Photogrammetry. If it is determined that the target layout does not provide sufficient ground control to meet the accuracy requirements, additional photo identifiable points shall be selected, marked and provided to the IDOT for field data collection. 5.2 Photo identifiable Control Points When preflight targets are not provided by IDOT, photo identifiable points will be selected and annotated on the strip or block of digital frame imagery and provided in PDF format for use by field crews in locating and collecting data to establish coordinates for the points. Photo identifiable points can be identified as horizontal only control, vertical only control, or as 3 D control. Horizontal control points should be sharply defined and positively identified in the images. Vertical control should be located on fairly flat, unobstructed terrain. Photo identifiable control points shall be established on permanently fixed objects and shall have sufficient description to locate in the field and clarity to make precise measurements from the imagery. Ensure the selected points are not obscured by shadows or objects. When using pavement markings for photo control, the date of photography shall be a determining factor on their suitability. 2

3 5.3 Deliverables A PDF file shall be delivered that includes all images to be included in the aerial triangulation adjustment. All image titles shall be clearly visible in the PDF. In cases where there are multiple strips on a project, a PDF shall be created for each individual strip. Photo control points that fall in areas of overlapping strips shall be shown on all appropriate strips in the PDFs. The PDF file name shall include the SAP number, the strip number and the abbreviation PC, separated by underscores. Example: 0331_STRIP_1_PC.pdf Vertical control is shown as a green circle with point numbers beginning at Horizontal Control is shown as a red triangle with point numbers beginning at D Control is shown as a yellow circle inside a triangle with point numbers beginning at There shall be a title, with the information shown, and north arrow placed in a non obtrusive location in the pdf. 3

4 6 Aerial Triangulation Analytical aerial triangulation methods and procedures shall be used to establish ground coordinates on pass and tie points, minimizing field surveyed points and providing the necessary control for each stereo model to perform subsequent photogrammetric operations. The use of ABGPS/INS data is required in combination with the ground control. The contractor shall perform a fully analytical bundle adjustment using weighted least squares adjustment. A minimum of nine precisely marked supplemental control points shall be established for each image, with five points measured near the corners and nadir point of the image. The first and last images in each strip shall have a minimum of six supplemental control points. Tie points shared between flight lines should be created as geometrically warranted between overlapping flight lines. The analytical computations must result in a root mean square (RMS) error at the control points of one part in ten thousand (1:10,000) Above Mean Ground Level(AMGL). 6.1 Imagery Digital imagery provided by IDOT will meet IDOT Digital Vertical Aerial Imagery Specifications dated February 5, Camera Calibration Report A Calibration Certificate for a certified digital camera system will be provided. This certificate is generated by the camera vendor and serves as verification of the camera system. 6.3 Airborne Global Positioning System and Inertial Navigation System Differential ABGPS/INS data collected onboard the aircraft during the photography mission provide additional observations that can reduce the number of field surveyed ground control points. This data has been collected and processed by the IDOT aerial photography vendor per IDOT Digital Vertical Aerial Imagery Specifications dated February 5, ABGPS/INS data will be supplied by IDOT for each project in ASCII format. 6.4 Deliverables Aerial Triangulation Report which includes: Equipment, processes and computer programs used for aerial triangulation Problems encountered and how they were resolved Identify any photo control points withheld Adjusted coordinates of ground control points, pass points and tie points Exterior orientation parameters for each image Electronic aerial triangulation solution files compatible with Imagestation software 4

5 7 Digital Stereo Compilation Mapping shall be compiled using photogrammetric mapping systems to produce 3D mapping products. The appropriate MicroStation seedfile, which identifies the geographic coordinate system, shall include models for plan (TOPO_0100 model) and terrain (ALL_DTM model) details to be compiled within the project boundary provided. The MicroStation photogrammetric mapping file (PHO extension) is intended to compliment the data in the MicroStation field survey file (SUR extension) provided by IDOT and created in accordance with Chapter 40 of the Design Manual. There shall be no duplication or gaps between the survey and the photogrammetrically compiled data. The boundary of each individual stereo model shall be defined by a polygon in a MicroStation stereo model boundary model. During compilation, if obscured areas without adequate field survey are discovered, a request shall be made to IDOT for additional field survey to cover the obscured area. Horizontal and vertical accuracies of products created shall meet or exceed the American Society for Photogrammetry and Remote Sensing Class 1 Accuracy Standards for Large Scale Maps Part 1&2 March All mapping information shall be generated in accordance with the seed files, symbols, levels, styles and line weights defined in Chapter 20A B of the IDOT Design Manual. MicroStation and GEOPAK TIN files shall be named to associate them with the project number. The first two digits of the file name are the county numbers, the next three digits are the route (the first digit being a zero for routes with two numbers) and the last three digits is the number in the parentheses. Example: Project Number BRF 034 1(96) MicroStation file name: pho 7.1 TOPO_0100 Model for Plan Details 3D vector and point representations of features at a mapping scale of 1:1,200 shall be provided in the TOPO_0100 model of the MicroStation seed file. This model shall contain all features which are visible or identifiable on the aerial photography. 7.2 Digital Terrain Model (DTM) Model 3D breaklines and mass points shall be compiled in the MicroStation DTM model. Breaklines shall be added where there are changes in the slope of the ground surface. The distance between points along breaklines shall not exceed 100 ft. Breaklines shall not cross or overlap. Mass point grid spacing shall not exceed 25 ft. A GEOPAK TIN shall be generated to include all breaklines and mass points with accurate ground elevations from the DTM models in the PHO and SUR files. In the contour model in the pho file, 1 foot contours with 5 foot index contours shall be generated from the GEOPAK TIN. 7.3 Deliverables V8 MicroStation file with the following models: 5

6 (3D) Topo_0100 includes all features within the project limits with specific attributes (3Dd) ALL_DTM model includes breaklines and mass points used to generate the TIN a combination of the data in the Plotter DTM model and the Survey DTM model (3D) Contours includes 1 foot contours generated from the GEOPAK TIN (3D) Plotter DTM includes the stereoscopically compiled terrain data (3D) Survey DTM includes a copy of the field survey Field DTM model. The attributes can be changed to a unique symbology for TIN creation. Stereo Model Boundary model includes labeled polygons surrounding the area of each neat model and identifying the photo numbers at the principal point. A GEOPAK TIN which includes breaklines and mass points from the DTM models in the PHO and SUR files. 8 Georeferenced Digital Orthorectified Imagery The georeferenced digital orthorecitified images (ortho) produced shall encompass the area of stereo coverage in the imagery provided, unless stated otherwise. The DTM used in the ortho production shall include the aerial and ground surveyed terrain within the project mapping boundary. Beyond the mapping boundary, the DTM shall include mass points with a grid spacing of up to 100 ft and breaklines, where necessary, to achieve the accuracy desired. The digital orthos shall be rectified to the ground and bridge deck surfaces. A tagged image file (TIF) with a ground sample distance of 0.25 shall be mosaiked for each strip of imagery. This tiled TIF shall have a JPG compression factor of 15 with 8 averaged overviews. The orthoimagery shall be free of image smears, noticeable seamlines, artifacts, voids, and misalignment errors. The orthoimagery shall have a uniform tone and brightness. A world file for TIF (TFW) shall be provided for each orthorectified strip that geo references the image to the project coordinate system provided by IDOT. Each TIF shall be named to define the images included in the ortho. For example, images titled 1444HPSD01_1_12 through 1444HPSD01_1_20 are included in a TIF for strip 1 and the ortho shall be named 1444HPSD01_1_12 20.tif. Images 1444HPSD01_2_225 through 232 are included in a TIF for strip 2 and the ortho shall be named 1444HPSD_2_ tif 8.1 Deliverables TIF and TFW file for each strip of photography. 6