Specifications
Specification | Metro HD Program – Acquisition |
Nominal Image GSD (Planned) | 5.0 centimeter (cm) |
LiDAR Density (Planned) | Target: 20 points per m2, all swaths Minimum allowed: 8 points per m2, all swaths |
Aerial Accuracy | RMSE x/y = 15 cm RMSE z = 25 cm |
Ortho Accuracy | RMSE x/y 25 cm RMSEr = 35.4 cm CL95 = 61.2 cm
Data sets are produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 25 (cm) RMSEx / RMSEy Horizontal Accuracy Class, which equates to Positional Horizontal Accuracy +/- 61.2 cm at a 95% confidence level. |
LiDAR Accuracy | RMSEz = 10 cm CL95 = 19.6 cm In open, non-vegetated terrain Data sets are produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10 (cm) RMSEz Vertical Accuracy Class equating to an NVA = +/- 19.6 cm at 95% confidence level and VVA = +/- 29.4 cm at the 95th percentile. |
Minimum Sun Angle | 30° minimum; however, every effort should be made to acquire the downtown core and any tall building filler lines at the highest solar elevation possible in the day. |
Cloud/Cloud Shadow | Must be less than 5% per 40 square kilometer block. Obscured details must not include urban areas or housing and roads in rural areas. Every effort will be made to remove clouds using adjoining imagery. In these limited circumstances, visible seam lines along cloud edges are acceptable. |
Smoke/Fire | See cloud cover. |
Persistent Smoke (volcano, factory, crop burn, etc.) |
See cloud cover. |
Snow/Ice Cover | Permanent snow/ice is acceptable. Seasonal snow/ice is acceptable if obscured details are not of high significance or represent key man-made, natural, or cultural features on the ground (e.g., paved roads, agricultural field boundaries, housing, communication routes). |
Specular Reflection | Must not be detrimental to the image appearance or impede the ability to extract information from the imagery. |
Flooding/Standing Water | Acceptable if obscured details are not of high significance or represent key man- made or cultural features on the ground (e.g., paved roads, agricultural field boundaries, housing, communication routes). |
Maximum Allowable Orthomosaic Seamline Offset | 25 cm (x/y) |
Relative Stereo Accuracy | 10 cm (x/y), 15 cm (z) |
LiDAR Interswath Accuracy | RMSDz: ≤ 6.0 cm |
LiDAR Intraswath Accuracy | RMSDz: ≤ 8.0 cm |
Side Overlap | Urban areas planned 60% or greater with CityMapper (Nadir Image) |
Forward Overlap | Urban areas planned 80% or greater with CityMapper (Nadir Image) |
Non-pixel Data | DN values of 0 and 255 reserved for non-data |
Sensor and Lens Artifacts | Imagery should be free of artifacts caused by defects in the image sensor or lens pollution. |
Band-to-band Pixel Misregistration | ≤ 0.5 pixels and no perceivable color fringing |
Image Blur Due to Turbulence | Image blur caused by turbulence is not acceptable. |
Radiometry and Color | Dynamic range adjustment to develop 8-bit imagery from digital camera raw images shall preserve feature detail across the full image histogram: in highlights, mid-tones, and shadows. The image’s appearance must be a realistic representation of the color on the ground. Color and radiometry adjustments shall be made to minimize the impact of atmospheric and solar variance within orthomosaic and aerial images. The color and radiometry of images should be consistent across different flights within a block. Neutral color balance shall be preserved on manmade features (asphalt, concrete, rooftops). Neutral color shift due to histogram-based image adjustment methods is not permitted. Neutral objects shall have a DN difference of no more than 5 for any RGB triplet. Sample images may be requested to confirm that radiometry and color meet expectations. |
Feature Warp/Smear | Bridge/freeway/causeway warp/smear is not acceptable. Where geometric fidelity of a feature is compromised, or pixel stretch occurs, special care will be taken to ensure the orthoimage is a realistic representation of real-world details and oversimplification or unrealistic fabrication has been minimized. |
Building Seamline Sheer | Visible joins between ortho-images and flight lines within each block should be avoided but will be accepted under the following conditions: they do not hide detail or adversely affect the ability to extract information from the image; they do not stretch the entire length of the seamline, e.g., clearly outlining entire images; they do not impact geometric fidelity (no change in shape or alignment between images); there is not positional shift between images along visible lines; and the other color difference is slight and/or well graduated and consistent both within the block and with edge matched blocks in the imagery layer they are along cloud edges remaining from the cloud cover conformity. |
Building Lean | Supplemental flight lines will be added as required to minimize building lean. Buildings over 120 ft tall that are not at nadir will be assessed for lean. Seamlines will be moved to use the most nadir data to alleviate road occlusions only. The objective is to have the center line of roads visible. |