Photogrammetry Specifications

  • Accuracy

    • Aerotas performs numerous tests and monitors every project to ensure the highest accuracy possible. However, accuracy ultimately depends on the quality of ground data. Because of this, Aerotas cannot provide an independent guarantee of accuracy. If, however, accuracy validation and guarantees are required, Aerotas can assist in certifying accuracy to ASPRS Positional Accuracy Standards.

  • Coordinate System

    • Aerotas supports all coordinate systems and datums for all projects. This includes any form of NAD83, WGS84, arbitrary, local, or assumed datum, as well as any vertical datum that you use. We ensure that all our final deliverables match exactly with your existing ground survey data.

  • Notification Criteria

    • Aerotas uses numerous different methods to assess if there is any error in a project. We use a threshold of approximately 0.1’ (3cm) acceptable error on a project, beyond which we will always notify the client. When data quality does not meet our standards for whatever reason, we will notify the client. This includes, but is not limited to, circumstances in which we determine that there is:

      • Insufficient quantity of GCPs

        • fewer than 1 GCP per 100 photos (non RTK projects)

        • fewer than 5 total GCPs

      • Bad distribution of GCPs

        • more than 20 flight lines between GCPs (75/75 overlap)

        • GCP visible in fewer than 4 images

      • Inaccurate or moved ground control

        • more than 0.1’ (3cm) error on any GCP

      • Improper flight overlap

      • Improper flight altitude

      • Suboptimal camera settings

      • Possible damage to a camera / sensor / lens

  • File Sizes

    • The full resolution photogrammetry files are very large, and cannot be handled by every software. CAD programs are especially limited in managing large files. It is for this reason that Aerotas offers a CAD-Friendly orthophoto, and linework drafting services. The client is free to create any custom size, resolution format, or tiling from the full resolution files that we deliver, however, this is not a process that we actively support.

  • CAD-friendly Specifications

    • Our CAD-Friendly files are typically between 100MB and 200MB in size, and are delivered in a compressed, geotiff (.tif) format with geolocation data embedded in the file. However, a world file (.tfw) is included as well with geolocation data as this can assist in the importing of the file into certain CAD programs. Because there are inherent limits on the acceptable size of images in CAD programs, larger projects will have to be compressed more aggressively, resulting in a lower resolution orthophoto.

  • Edge Accuracy

    • Aerotas includes the full, uncut orthophoto and DSM as part of our deliverables. However, accuracy on the edges of these deliverables will be degraded from the accuracy in the center of the project. We include this edge data in addition to the central data in case the visual information is useful for context in surveying projects, even if it is not required. The far edges of the photogrammetry deliverables will often include artifacts

  • Accuracy In-Between Ground Control Points

    • The further a point on a project is from any ground control points, the higher the possibility of error on that point. The exact amount of error is nearly impossible to determine without the use of checkpoints on a project. If Aerotas believes that a low quantity or poor distribution of ground control points will significantly impact the accuracy of a project, we will notify the client.