Attribute_Accuracy_Report:
Camera EXIF position data are generally accurate to within a few hundred meters, and time data are accurate to within a few minutes. Camera clock was UTC through 7 March 2018, and switched to PST starting 29 March 2018 (to simplify processing across UTC date changes).
RGB values are 8-bit, generally not saturated or underexposed. In a few cases of high or low light conditions, some imagery may be under- or over-exposed.
Data are considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details, and to examine EXIF data for individual flights to determine camera settings such as exposure mode and shutter speed.
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
A formal accuracy assessment of the horizontal positional information in the image data set has not been conducted. Most images have EXIF stamps from a consumer-grade GPS, updated every few seconds. Position accuracy for these images is generally within about 200m. Some images may lack GPS position in EXIF data, but in most cases, we apply interpolated positions or positions derived through onboard survey-grade GNSS or 4D structure-from-motion. High-precision positions, when available, are published as a flight derivative product with separate metadata describing their derivation and accuracy.
Process_Step:
Process_Description:
Acquisition -- Aerial imagery was collected using a DOI-contracted aircraft operated by EcoScan Resource Data LLC and piloted by Bob Van Wagenen. Integrated GNSS and Camera hardware designed and built by the U.S. Geological Survey, Pacific Coastal and Marine Science Center and mounted inside the aircraft was oriented to capture [orientation] imagery through a port in a cargo door. Images were acquired in camera raw format. The camera is triggered by an intervalometer integrated with a survey-grade GNSS and triggered using a PPS signal from the GNSS, routed through a microcontroller to the camera remote shutter, and recording an event mark to the GNSS when the shutter is actuated, through the flash-sync port on the camera. A consumer-grade GPS attached to the camera keeps camera time synced with UTC time and provides approximate coordinates for EXIF data.
Process_Date: 20190311
Source_Produced_Citation_Abbreviation: raw imagery
Source_Produced_Citation_Abbreviation: raw GNSS data
Process_Step:
Process_Description:
Image renaming -- Raw Images are renamed using Phil Harvey's EXIFTOOL with the following command:
exiftool -r -d %Y%m%d%H%M%S "-testname<CAM${SerialNumber;s/\d{4}//}_${SubSecDateTimeOriginal}_${SubSecTimeOriginal}%-c.%e" -ext nef .\*
files follow the following naming convention: {CAM###}_{YYYYMMDDHHMMSS_ss}.jpg, where {CAM###} is the last 3 digits of the camera serial number, preceded by the letters "cam", and where {YYYYMMDDHHMMSS_ss} is the image acquisition time in {YearMonthDayHourMinuteSecond_hundredths} expressed in 24-hour time, as recorded by the camera's internal clock and written to the SubSecondDateTime field in the image EXIF data (for example CAM001_202009182311_50 would be the timestamp for an image with a SubSecondDateTime EXIF time/date stamp of September 18th, 2020 at 11:11.50 pm (See accuracy report for details on time accuracy)
Process_Date: 2019
Process_Step:
Process_Description:
Image conversion -- renamed images are batch- converted from .camera raw format to a format compatible with photogrammetry processing software. Software versions, conversion date, and other parameters are recorded in individual image EXIF data.
Process_Date: 2019
Process_Step:
Process_Description:
Image QA/QC -- original and converted images are counted, and the beginning and end of the survey are reviewed to cull extraneous images such as camera testing or inadvertently triggered images and place both raw and converted images in an "outtakes" folder for a given flight (outtakes might not be released and are not processed). A multipage tiff contact sheet of images is created to allow quick review ensuring that (a) conversion was successful with no corrupted imagery, and (b) "extra" imagery not capturing the intended view is culled and placed in the "outtakes" folder. If corrupted converted images are found, imagery is re-converted. If extra images are found, raw and converted images are moved to the "outtakes" folder. This step is iterated until a collection of valid images remains. Note that in some cases, images of water may be retained if there are visible or potentially visible bathymetric features, aquatic vegetation, or objects in the scene that may be useful for future data applications.
The multipage contact sheet is generated with the open-source image processing system GraphicsMagick using the command:
gm.exe montage -compress JPEG -quality 85 -sampling-factor 4:4:4 -font Arial-Narrow -pointsize 10 -tile 9x7 -label %t -geometry "135x90+1+0>" <ImageFolderPath>*.<ext> -define tiff:bits-per-sample=8 <SurveyFolderName>_thumbnail_contact_sheet.tif
where <ImageFolderPath> is the path to the directory of images, <ext> is the image extension, and <SurveyFolderName> is the unique name of the survey folder.
The GraphicsMagick version is recorded to the multipage contact sheet in the tiff metadata under the TIFFTAG_SOFTWARE tag.
A csv file of a subset of image EXIF tags is then generated with the following exiftool command:
exiftool -Model -LensID -ExposureProgram -FocalLength -ExposureTime -FNumber -ISO -SubSecDateTimeOriginal -DateTimeOriginal -GPSDateTime -GPSLatitude# -GPSLongitude# -GPSAltitude# -GPSPosition# -GPSAltitudeRef -GPSSatellites -CreatorTool -CameraProfile -SerialNumber -ImageNumber -f -csv -ext <ext> <SurveyFolderName>_EXIF.csv
where <ext> is the file extension of the converted images used for photogrammetry and <SurveyFolderName> is the name of the folder for a specific survey.
The csv file is processed with a custom python script to add camera positions from GNSS- or SfM-derived position files, or to interpolate or extrapolate positions, depending on available data.
Process_Date: 2019
Process_Step:
Process_Description:
GNSS data processing -- when collected, GNSS data are post-processed to derive the precise position of ground control points, check points, and/or the GNSS antenna at the time of image acquisition. If necessary for rapid processing, approximate (provisional) positions are produced from rapid ephemeris data. After precise ephemerides are available, GNSS data are post-processed to calculate GNSS trajectory, and precise positions are derived from station occupations or event marks recorded with precision timing, placed along the GNSS trajectory. Processing workflows, accuracy estimates, software and version are detailed in GNSS metadata. Camera and ground control positions are post-processed together with images, camera lever arm data and photogrammetric software to derive accurate camera position and pose.
Process_Date: 2019
Process_Step:
Process_Description:
Photogrammetric Processing -- 3D or 4D structure-from-motion (SfM) processing, as described in Over and others (2021) and Warrick and others (2017), is used to derive camera positions for surveys missing position data if necessary. This processing is done with reduced accuracy to provide approximate location only.
Process_Date: 2019
Process_Step:
Process_Description:
Imagery EXIF coordinates reconciliation -- EXIF camera positions are not intended to be suitable accuracy for precise photogrammetric surveys but are used to populate the EXIF metadata field and locate the image in space relative to other images for reference purposes. GNSS/SfM position data published separately from images should be used for SfM reconstruction if available. Camera positions are not always recorded for individual images due to GNSS collection conditions, malfunctioning equipment, or other reasons.
Depending on availability of position data, coordinates for image EXIF position data are recorded to imagery with one of the following methods, with the appropriate indicator written to the EXIF:GPSAreaInformation tag:
1) Image positions recorded to the EXIF field with the attached consumer-grade GPS device are labeled with the EXIF tag EXIF:GPSAreaInformation="camera-integrated GPS".
2) Image positions recorded to the EXIF field from timing-based GNSS event marks are labeled with the EXIF tag EXIF:GPSAreaInformation="GNSS event mark".
3) Image positions derived from 3D or 4D SfM processing with or without ground control points are labeled with the EXIF tag EXIF:GPSAreaInformation="structure-from-motion".
4) Image positions interpolated or extrapolated from between GPS, GNSS, or SfM-derived positions using adjacent image positions and a time-averaged velocity and direction algorithm are labeled with the EXIF tag EXIF:GPSAreaInformation="interpolated" or (EXIF:GPSAreaInformation="extrapolated".
5) If imagery needs to be published without more precise positioning to support emergency response or timely best science, or if no other way exists to locate images more accurately, then an approximate location is assigned to some or all images based on best estimate of location. This may include assigning a single location to all images to approximately locate them based on the geographic area of a survey. Any images located with this method are labeled with the EXIF tag EXIF:GPSAreaInformation="estimated approximate location"
Process_Date: 2019
Process_Step:
Process_Description:
Image EXIF annotation -- Additional information was added to individual image EXIF tags using the command-line 'exiftool' software with the following command, as appropriate:
#tags for provisional data
exiftool ^
-P ^
-IPTC:Credit="U.S. Geological Survey" ^
-IPTC:Contact="pcmsc_data@usgs.gov" ^
-EXIF:Copyright="Public Domain" ^
-XMP:UsageTerms="These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data." ^
-overwrite_original *.JPG
#tags for approved data
exiftool ^
-P ^
-IPTC:Credit="U.S. Geological Survey" ^
-IPTC:Contact="pcmsc_data@usgs.gov" ^
-EXIF:Copyright="Public Domain" ^
-XMP:UsageTerms="Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty." ^
-EXIF:ImageDescription="[single_image_EXIF_desc]" ^
-XMP:AttributionURL="
https://doi.org/10.5066/P9M3NYWI ^
-EXIF:GPSAreaInformation="[position_method]" ^
-EXIF:GPSMapDatum="EPSG:4326 (WGS 84)" ^
-overwrite_original *.JPG
tags were then duplicated to XMP headers to increase tag compatibility for image viewing software with the following exiftool command
#tag duplication per phil harvey
exiftool ^
-P ^
"-XMP-photoshop:Credit<IPTC:Credit" ^ "-XMP-iptcCore:CreatorWorkEmail<IPTC:Contact" ^
"-XMPdc:Rights<EXIF:Copyright" ^
"-XMP-dc:Description<EXIF:ImageDescription" ^
"-XMP-exif:all<GPS:all" ^
"-XMPexif:GPSLatitude<Composite:GPSLatitude" ^ "-XMP-exif:GPSLongitude<Composite:GPSLongitude" ^
"-XMPexif:GPSDateTime<Composite:GPSDateTime" ^ "-XMP-photoshop:DateCreated<EXIF:DateTimeOriginal" ^
"-XMPxmp:ModifyDate<EXIF:ModifyDate" ^
"-XMP-dc:Creator<EXIF:Artist" ^
"-XMP-tiff:Make<EXIF:Make" ^
"-XMPtiff:Model<EXIF:Model" ^
-overwrite_original *.JPG
