Control / QC Checkpoint Creation: A total of 68 ground based photo control points were established throughout the project area using a combination of conventional and GPS survey methods in order to support softcopy aerotriangulation and photogrammetric mapping meeting the accuracies specified in this Scope of Work. This control supplemented the exposure station control obtained from the onboard Airborne Global Positioning System (ABGPS) and Inertial Measurement Unit (IMU). Photo control points established for this project have a combined local and network accuracy at 95% confidence of less than or equal to five (5) centimeters horizontally and vertically as determined by the residuals of the network adjustment. Ground control collection followed requirements set forth in USGS Contract No. G10PC00026; USGS Task Order: G15PD00279; Requisition Reference Number: 0040202231, and were modified as appropriate to accommodate the specifications related to ABGPS collection specific to these end photogrammetric mapping requirements. All horizontal and vertical control was prepared under the supervision of Professional Land Surveyors licensed in the states of New Jersey and Pennsylvania. Date is approximate.
Imagery Acquisition: Digital aerial imagery was obtained using a large format Microsoft UltraCam Falcon and Eagle equipped with Airborne GPS/IMU covering the entire State of New Jersey. A total of 51 flight lines with 4171 frames were collected in the spring of 2015 in multi-spectral (RGB and NIR) 16 bits format. This includes the acquisition of supplemental imagery over the cities of Atlantic City (2 Flight Lines; 18 Frames), Camden (2 Flight Lines; 12 Frames), Jersey City (1 Flight Line; 6 Frames), Newark (2 Flight Lines; 14 Frames), and Trenton (2 Flight Lines; 16 Frames) that was used to minimize building lean in the orthophotography production process. The imagery was acquired at an altitude above mean terrain of 16,480' to yield a raw pixel resolution of 0.96' suitable for photogrammetric mapping and orthophoto production. The imagery was collected during leaf off conditions in the spring of 2015 under conditions free from clouds and cloud shadows, smoke, fog, haze, light streaks, snow, ice on water bodies, flooding, and excessive soil moisture. The imagery is also mostly free from foliage, but leaves were beginning to come out towards the end of acquisition in May. In order to minimize shadow conditions, imagery was obtained during the period of the day when the sun angle was greater than 35 degrees. For New Jersey, the sun angle was greater than 35 degrees south of US Highway 1 and greater than 40 degrees north of US Highway 1. The imagery consisted of blue, green, red and near-infrared bands. Imagery for the photogrammetric mapping and digital orthophotos was captured according to the USGS Contract No. G10PC00026; USGS Task Order: G15PD00279; Requisition Reference Number: 0040202231 regarding, snow, haze and cloud cover, and modified as appropriate to accommodate the requirements specific to UltraCam technologies and as specified in this scope of work.
Aerotriangulation Process: Softcopy aerotriangulation was performed on 2 blocks of imagery. The airborne GPS/IMU data, GPS ground control, and image coordinate measurements were utilized to allow the direct computation of the exterior orientation parameters for each image frame to support the photogrammetric process and orthophoto production. The adjusted Root Mean Square Error (RMSE) of all horizontal and vertical control points used for any single block adjustment was 1.0 foot or better. At the same time, residuals on each refined image coordinate remain less than 10 microns and residuals on any horizontal or vertical control point did not exceed plus or minus 0.075 meters. Within each block, the QA ground survey coordinates were within two times the RMSE (1 meter) of the corresponding AT derived coordinates. Date is approximate.
Digital Terrain Model Creation: This process involved the development of seamless topographic landform elevation dataset utilizing existing public domain elevation data sets to support the production of digital orthophotography that meet or exceed required orthophoto horizontal accuracy. Existing terrain surfaces utilized for this project included the maximum utilization of government supplied airborne topographic LiDAR bare earth data sets of various vintages, accuracies and post spacing as well as DEM data from the 2015 New Jersey Orthophoto Project as needed to complete a 2015 Statewide orthophoto DEM source. The topographic features included a grid of elevation points and may include break lines that define ridges, valleys, edge of water, transportation features and abrupt changes in elevation. The final DTM is suitable for orthophoto production only (not suitable for contour generation). The DTM is used to then generate a Triangulated Irregular Network (TIN) to support orthophoto production. Date is approximate.
Orthophotography Creation: Utilizing all four bands [blue (B), green (G), red(R) and near-infrared (IR)] digital orthorectification was performed using bilinear interpolation algorithms resulting in a spatial and radiometric transformation of the digital image from line/sample space into NAD83 (2011) State Plane New Jersey, US Survey Feet. The interior and exterior orientation parameters from the aerotriangulation process were used to project each pixel into the ground coordinate system, while the ortho grade DEM/DTM was used to correct for relief displacement. Radiometric correction software and techniques were used to create orthophoto files that minimize the appearance of image seams and without loss of feature signature. Orthophotos are checked for geometric accuracy, image quality, and are tonally balanced to produce a uniform contrast and tone across the entire project. The individual overlapping orthophoto frames were mosaicked together. The ortho photos meet a horizontal accuracy of 4 feet or less at 95% confidence level when compared to higher accuracy check points based on NSSDA testing standards. Date is approximate.
GeoTIFF imagery tiles in NAD_1983_2011_StatePlane_New_Jersey_FIPS_2900_Ft_US (EPSG::6527) were reprocessed using LizardTech GEOEXPRESS 9.5 to create lossless MrSID MG4 format. These images were indexed to create a WMS using LizardTech Express Server.
Natural color orthoimagery is organized in three color bands or channels which represent the red, green, and blue (RGB) portions of the spectrum. Each image pixel is assigned a triplet of numeric values, one for each color band. Numeric values range from 0 to 255.