Chimney Bluffs digital elevation model (DEM) from low-altitude aerial imagery from unmanned aerial systems (UAS) flights over of the Lake Ontario shoreline in the vicinity of Chimney Bluffs, New York in July 2017 (32-bit floating point GeoTIFF image)

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Frequently anticipated questions:

What does this data set describe?

Title:
Chimney Bluffs digital elevation model (DEM) from low-altitude aerial imagery from unmanned aerial systems (UAS) flights over of the Lake Ontario shoreline in the vicinity of Chimney Bluffs, New York in July 2017 (32-bit floating point GeoTIFF image)
Abstract:
Low-altitude (80-100 meters above ground level) digital images were obtained from a camera mounted on a 3DR Solo quadcopter, a small unmanned aerial system (UAS), in three locations along the Lake Ontario shoreline in New York during July 2017. These data were collected to document and monitor effects of high lake levels, including shoreline erosion, inundation, and property damage in the vicinity of Chimney Bluffs State Park, New York. This data release includes images tagged with locations determined from the UAS GPS; tables with updated estimates of camera positions and attitudes based on the photogrammetric reconstruction; tables listing locations of the base stations, ground control points, and transect points; geolocated, RGB-colored point clouds; orthomosaic images; and digital elevation models for each of the survey regions. Collection of these data was supported by the Federal Emergency Management Agency, the State of New York Departments of State and Environmental Conservation, and the USGS Coastal and Marine Geology Program and was conducted under USGS field activity number 2017-042-FA.
Supplemental_Information:
For more information about this field activity, see https://cmgds.marine.usgs.gov/fan_info.php?fan=2017-042-FA.
  1. How might this data set be cited?
    U.S. Geological Survey, 2018, Chimney Bluffs digital elevation model (DEM) from low-altitude aerial imagery from unmanned aerial systems (UAS) flights over of the Lake Ontario shoreline in the vicinity of Chimney Bluffs, New York in July 2017 (32-bit floating point GeoTIFF image): data release DOI:10.5066/P9W81QEZ, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Sherwood, Christopher R., Brosnahan, Sandra M., Ackerman, Seth D., Borden, Jonathan, Montgomery, Ellyn T., Pendleton, Elizabeth A., and Sturdivant, Emily J., 2018, Aerial imagery and photogrammetric products from unmanned aerial systems (UAS) flights over the Lake Ontario shoreline at Chimney Bluffs, New York, July 14, 2017: data release DOI:10.5066/P9W81QEZ, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Sherwood, C.R., Brosnahan, S.M., Ackerman, S.D., Borden, Jonathan, Montgomery, E.T., Pendleton, E.A., and Sturdivant, E.J., 2018, Aerial imagery and photogrammetric products from unmanned aerial systems (UAS) flights over the Lake Ontario shoreline at Chimney Bluffs, New York, July 14, 2017: U.S. Geological Survey data release, https://doi.org/10.5066/P9W81QEZ.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -76.9161747186
    East_Bounding_Coordinate: -76.904511315
    North_Bounding_Coordinate: 43.2919533659
    South_Bounding_Coordinate: 43.285587981
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5b28587de4b0592076260e47/?name=2017042FA_ChimneyBluffs_DEM_browse.jpg (JPEG)
    Browse graphic of a portion of the DEM generated from photogrammetry and low-altitude aerial images obtained with unmanned aerial systems (UAS).
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 14-Jul-2017
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 13720 x 18620, type Pixel
    2. What coordinate system is used to represent geographic features?
      The map projection used is Universal Transverse Mercator.
      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -75.00000
      Latitude_of_Projection_Origin: 0.000
      False_Easting: 500000.0000
      False_Northing: 0.0000
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.05
      Ordinates (y-coordinates) are specified to the nearest 0.05
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222101.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988 (NAVD88)
      Altitude_Resolution: 0.00001
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    There are no attributes associated with this GeoTIFF however the pixel values of the 32-bit image are elevation values as exported from Agisoft Photoscan. The "no data" value is set to -32767. Data values represent elevation in meters referenced to NAVD88. Note the full precision of the elevation as exported from the Agisoft Photoscan software is 0.00001 m although that is several orders of magnitude finer than the accuracy of the data.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Sandra Brosnahan
    Physical Scientist
    384 Woods Hole Road
    Woods Hole, Massachusetts

    508-548-8700 x2265 (voice)
    508-457-2310 (FAX)
    sbrosnahan@usgs.gov

Why was the data set created?

The gridded DEM surface estimates the elevation of the land surface at mid-day low-tide on 14 July, 2017 in the Chimney Bluffs study area. It was created to demonstrate the use of structure-from-motion (SfM) for shoreline research and to provide a means to measure the accuracy of the elevation measured through SfM photogrammetry. It is released to provide an elevation dataset that is more accessible than the LAZ elevation point cloud for the general user.

How was the data set created?

  1. From what previous works were the data drawn?
    geotagged aerial digital images (source 1 of 2)
    U.S. Geological Survey, unpublished material, Field geotagged aerial imagery from unmanned aerial systems (UAS) flights over of the Lake Ontario shoreline in the vicinity of Chimney Bluffs, New York in July 2017.

    Type_of_Source_Media: raster digital images
    Source_Contribution:
    These are the images geotagged in the field and used to produce the subsequent photogrammetric products. The images available from the larger work citation of this data release have updated geotag information.
    GCPs (source 2 of 2)
    U.S. Geological Survey, 2018, Ground control point and transect locations associated with images collected during unmanned aerial systems (UAS) flights over The Lake Ontario shoreline in the vicinity of Chimney Bluffs, New York in July 2017: data release DOI:10.5066/P9W81QEZ, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: text data files
    Source_Contribution:
    The ground control points (GCPs; not transect points - see metadata for that dataset available from the larger work citation for more information) were used to geolocate the photogrammetric products.
  2. How were the data generated, processed, and modified?
    Date: Sep-2017 (process 1 of 3)
    Digital elevation models (DEM) for the Lake Ontario projects were constructed using photogrammetry software (Agisoft Photoscan Professional v. 1.3.2) and digital images taken approximately 80 and 100 m above the ground on July 10 - 14, 2017, with a Ricoh GRII digital camera mounted in a 3DR Solo quadcopter operated the U.S. Geological Survey. This DEM is the product from one of several photogrammetry projects from field activity 2017-042-FA. Two projects incorporated flights over Braddock Bay on July 10 and 11, 2017 (Braddock West, Braddock East); four were used for flights in the vicinity of Sodus Bay on July 12, 13, and 14, 2017 (Lake Bluff / Crescent Bar, Crescent Bar / Charles Point, Sodus North, and Greig Street); and one project incorporated flights over Chimney Bluffs on July 14, 2017. The projects combined images with 5 to 27 ground control points to produce geolocated, colored (red-green-blue schema) point clouds. This DEM, for the Chimney Bluffs project, was created using a standard processing flow as described in the processing step below. Person who carried out this activity:
    U.S. Geological Survey, Woods Hole Coastal and Marine Science Center
    Attn: Christopher R. Sherwood
    Research Oceanographer
    384 Woods Hole Road
    Woods Hole, Massachusetts
    U.S.A.

    508-548-8700 x2269 (voice)
    508 457 2310 (FAX)
    csherwood@usgs.gov
    Date: 13-Sep-2017 (process 2 of 3)
    The following steps are the processing flow for creating digital elevation models from UAS flights:
    1. Geotagged images created in the field (see source citation) containing useful imagery from the survey area were imported into Agisoft Photoscan Professional v. 1.3.2 software using the “Add photos…” tool. Photos taken before and immediately after takeoff, photos taken immediately prior to and after landing, and photos with 100% water were not loaded into the project or not used if they were. Project coordinate system is set to EPSG::7660 WGS84 (G1150) geocentric coordinate system.
    2. Using ”Convert”, the coordinate system of the images (called “cameras” in Photoscan) was converted from native latitude/longitude WGS84 (G1150) coordinate system to meters in NAD83/UTM zone 18N (EPSG::26918).
    3. The photos were processed through an initial alignment and optimization procedure using the following settings:
    Alignment - Accuracy: “High”; Pair selection: “Reference”; Key point limit: 80,000; Tie point limit; 0 (unlimited). Adaptive camera model fitting option was selected.
    Optimization - Lens-calibration parameters f, cx, cy, k1, k2, k3, p1, and p2 were included; b1, b2, and higher-order parameters k4, p3, and p4 were not.
    4. The sparse point cloud (also known as tie points; created as a result of photo alignment and optimization) was edited using an iterative error-reduction procedure to filter the data. This was done in several iterations of a process called "Gradual Selection" to first to reduce reconstruction uncertainty (to a unitless value of 10) and then projection accuracy (to a weighted value of 3).
    5. Ground control points were created by first letting the software automatically detect markers where it finds all of the 4-ft square black/white targets deployed (false targets that are sometimes detected were manually deleted). The automatically-generated marker labels were manually changed to match the names in the survey notes and GCP location files.
    6. "Import markers” was used to load the GCP location files, which assigned coordinates (northing, easting, and elevation in UTM Zone 18 North meters in NAD83 and NAVD88 coordinate systems) from the location file to the detected markers. The locations of auto-detected markers were retained.
    7. Another round of "Gradual Selection" was done to reduce the reprojection error (to a value of 0.3 pixels, unless more than 10% of the points would be removed).
    8. A dense point cloud was then created with the parameters "High" quality and “Aggressive” depth filtering.
    9. A DEM was created with the parameters Source data="Dense Cloud" Interpolation="Enabled" Resolution="0.05"
    10. The DEM was exported in GeoTIFF format (2017-07-10_ChimneyBuffs_DEM_5cm.tif) along with a world file (tfw), then both were renamed to the AIM data release filenaming standard (e.g. 2017042FA_ChimneyBluffs_DEM.tif). Person who carried out this activity:
    U.S. Geological Survey, Woods Hole Coastal and Marine Science Center
    Attn: Christopher R. Sherwood
    Research Oceanographer
    384 Woods Hole Road
    Woods Hole, Massachusetts
    U.S.A.

    508-548-8700 x2269 (voice)
    508 457 2310 (FAX)
    csherwood@usgs.gov
    Date: 06-Aug-2020 (process 3 of 3)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    Horizontal positions of individual points in the poind that that was used to create the DEM were calculated by photogrammetric software and ground control points. There are several sources of potential error that affect the horizontal accuracy:
    1. The horizontal error estimate provided by Agisoft Photoscan as a result of alignment, optimization, and ground control processing procedures is 0.78 cm. This value is an RMS estimate of positional error at discrete locations within the orthomosaic.
    2. Ground control points were collected using a Spectra model SP80 GNSS receiver set to record XY locations with the national adjustment of 2011 (NAD83(2011) UTM zone 18N EPSG::6347), which differs from the Photoscan project coordinate system (NAD83/UTM zone 18N (EPSG::26918)). This difference may introduce an average additional 0.9 cm horizontally at the 95% confidence level according to the National Geodetic Survey (https://www.ngs.noaa.gov/web/surveys/NA2011/).
    3. Additionally, an assessment of repeated survey sites (from transect points) using the same equipment by the USGS Aerial Imagery and Mapping (AIM) group estimates an accuracy of the ground control point locations of 1.76 cm (horizontal) and 0.54 cm (vertical).
    The combination of the potential horizontal error is on the order of 3.44 cm. Although some portions of the map may contain much larger errors, up to 2 m horizontally. The horizontal coordinate system for the Point Cloud, DEM and Orthomosaic is NAD83/UTM zone 18N (EPSG::26918).
    It is also important to note: The UAS image locations are derived from a mRo GPS (u-Blox Neo-M8N / 3DR SOLO Upgrade), located on the UAS, which receives signals from GPS and GLONASS satellites in WGS84 (G1150) EPSG::7660. This location information is used by the Photoscan software to help with the initial alignment, however after photo alignment, these location data have no bearing on the project or the derivative product. Therefore the positional accuracy and potential errors of the GPS data attached to the input photographs is not propagated to the Photoscan project and therefore does not contribute to the overall horizontal accuracy of the products (Point Cloud, DEM and Orthomosaic).
  3. How accurate are the heights or depths?
    Vertical positions of individual points for the point cloud were calculated by photogrammetric software and ground control points. There are several sources of potential error that affect the vertical accuracy:
    1. The vertical error estimate provided by Agisoft Photoscan as a result of alignment, optimization, and ground control processing procedures is 1.98 cm. This value is an RMS estimate of positional error at discrete locations within the orthomosaic.
    2. Ground control points were collected using a Spectra model SP80 GNSS receiver that was receiving real-time differential corrections from a GNSS base station established in Chimney Bluffs, NY. The Z heights were reference to the NAVD88 vertical datum. An assessment of repeated survey sites using the same equipment by the USGS Aerial Imagery and Mapping group estimates a potential accuracy error of the ground control point locations of 1.76 cm (horizontally) and 0.54 cm (vertically).
    The vertical datum for the Point Cloud, DEM and Orthomosaic is NAVD88 (meters).
    It is also important to note: The UAS image locations are derived from a mRo GPS (u-Blox Neo-M8N / 3DR SOLO Upgrade), located on the UAS, which receives signals from GPS and GLONASS satellites in WGS84 (G1150) EPSG::7660. This location information is used by the Photoscan software to help with the initial alignment, however after photo alignment, these location data have no bearing on the project or the derivative product. Therefore the positional accuracy and potential errors of the GPS data attached to the input photographs is not propagated to the Photoscan project and therefore does not contribute to the overall vertical accuracy of the products (Point Cloud and DEM).
  4. Where are the gaps in the data? What is missing?
    This DEM was created from the filtered tie-points of the dense point cloud using the Agisoft Photoscan Professional (v. 1.3.2) photogrammetry software. Through a standardized filtering process, spurious points from the dense point cloud were eliminated and the all of the remaining tiepoints in the dense point cloud were used to generate a digital elevation model. That includes points that likely do not represent ground features such as trees, vegetation, cars, homes and other man-made structures as well as artifacts generated by moving water surfaces and or remaining erroneous tie points. These points are commonly eliminated through either automatic or manual classification, but have been retained in the desnse point cloud to allow experimentation with point classification methods. The completed Photoscan project for Chimney Bluffs, from which this DEM was created, used 1527 of the original 1665 imported images and contained more than 188 million points. The unedited point cloud and the orthomosaic are available in this data release at https://doi.org/10.5066/P9W81QEZ.
  5. How consistent are the relationships among the observations, including topology?
    All data were handled in a consistent manner. Photoscan software determines the photos used in the construction of the products (Point Cloud, DEM and Orthomosaic) based on the ability to align the photo and the usability of valid tie points within an image, and some photos of the take-off and landing were omitted by the processor during the import data phase. A tie point represents a point that the software determine to be common from one photo to the next. The camera locations CSV file in this data release (https://doi.org/10.5066/P9W81QEZ) indicates which photos were used to create the final products. The final point cloud used to construct this dataset was checked for accuracy by rotating the point cloud to view from multiple angles to ensure that obvious spurious points do not cause artifacts in the derivative products (DEM and Orthomosaic).

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints none
Use_Constraints Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? This data release contains a DEM in 32-bit floating point GeoTIFF format (2017042FA_ChimneyBluffs_DEM.tif), the world file (2017042FA_ChimneyBluffs_DEM.tfw) and the browse graphic (2017042FA_ChimneyBluffs_DEM_browse.jpg). FGDC CSDGM metadata (2017042FA_ChimneyBluffs_DEM.xml) accompanies the data.
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    To utilize these data an image processing or GIS software package capable of viewing a 32-bit Floating Point GeoTIFF image, or GIS software capable of utilizing web mapping or coverage services. Standard image viewing software cannot translate the elevation data from 32-bit floating point GeoTIFF image.

Who wrote the metadata?

Dates:
Last modified: 19-Mar-2024
Metadata author:
U.S. Geological Survey
Attn: Sandra Brosnahan
Physical Scientist
384 Woods Hole Road
Woods Hole, Massachusetts

508-548-8700 x2265 (voice)
508-457-2310 (FAX)
whsc_data_contact@usgs.gov
Contact_Instructions:
The metadata contact email address is a generic address in the event the person is no longer with USGS. (updated on 20240319)
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
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