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
RMSE x/y = 15 cm
RMSE z = 25 cm
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.
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.
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.
See cloud cover.
(volcano, factory, crop burn, etc.)
See cloud 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).
Must not be detrimental to the image appearance or impede the ability to extract information from the imagery.
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
Urban areas planned 60% or greater with CityMapper (Nadir Image)
Urban areas planned 80% or greater with CityMapper (Nadir Image)
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.
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.
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.