With all these methods, navigation is recorded at the same time as the video—either by a separate GPS device or using software within the camera. Navigation can be synchronized with the video during postprocessing back in the office or in real time in the field using special video-encoding hardware, which produces full motion video that's immediately compatible with the ArcGIS Full Motion Video add-in. Users can then view the video track line and digitize geographic features as the video plays.
When marine scientists return with a survey video, if the navigation data still needs to be synchronized, they use an FMV converter package that CSA developed to automatically integrate video and navigation data for use with ArcGIS for Desktop and ArcGIS Full Motion Video. The package lets users do batch calculations on the navigation data, inject the spatial information into the videos, and export a product that's ready for ArcGIS Full Motion Video.
Underwater video is often recorded continuously, so it can be cumbersome to pinpoint relevant sections of the video for analysis. To help scientists quickly find important locations, such as the start or end points for a survey, CSA's FMV converter package also creates bookmarks using point locations that are either provided ahead of time by GIS staff or collected in the field and matched to the navigation data. Linking the video to these navigational bookmarks helps scientists select a specific point of interest and view video track lines in relation to those points using ArcGIS for Desktop.
To do this, scientists open the map document and play the video in ArcGIS Full Motion Video. As the video plays, a locational pointer traces the camera's path in ArcGIS for Desktop. A track line showing the camera's trajectory is automatically drawn in the map document, allowing users to clearly see the camera's path. Background features, such as imagery, bathymetry (water depth), and survey points, can be loaded into the map document to aid in orientation, analysis, and visualization. At this point, users can begin an editing session. They then use feature templates to digitize features—such as submarine cables, fish and coral species, ocean bottom types, shoreline shape, and coastal habitat types—by clicking in the video window or on the map document to record feature locations.
A significant challenge of traditional full motion video analysis is that it is difficult to estimate the scale of the video. Without accurate measurements of the camera's field of view, the extent of quantitative analysis that can be conducted (such as feature density and video coverage area) is limited.
To address this issue, CSA utilizes an upgrade it created for the FMV converter package for ground-projected instantaneous field of view, which provides users with a continuous guide to the scale and orientation of the video image. This is an advanced component of the FMV converter package that can be used with video encoders in the field or during postprocessing in the office. Its custom algorithm calculates the size of the camera's field of view and inserts the result into the navigation file before it is embedded in the video. When the encoded video is played with ArcGIS Full Motion Video, a box is displayed on the image representing the camera's field of view. The box dynamically changes as the camera's angle and location change, so the field of view can be calculated for each video frame. The field of view bounding box can be overlaid onto any ArcMap feature, such as multibeam bathymetry, satellite imagery, survey points, or infrastructure features. Additionally, users can estimate the accuracy of the bounding box by comparing bounding box coordinates to measurements of known physical features in the survey area or an intentionally inserted object whose dimensions are known.
With this understanding of field of view, users can make advanced calculations of survey areas and observed features using ArcGIS for Desktop, Portal for ArcGIS, ArcGIS Online, and other mapping applications. To CSA's scientists, this approach has been useful for evaluating fish density in both shallow and deep-water coral reef habitats, assessing the integrity of underwater pipelines, and classifying different kinds of reefs and types of ocean floor.
For more information, visit CSA's website or contact Sarah Franklin, geospatial coordinator at CSA Ocean Sciences Inc., at 772-403-6098.