Introduction
Our goal is to process your data as quickly and efficiently as possible to ensure customer delight. We invest a significant amount of effort to process the data successfully the first time.
However, capturing these thousands of images might be challenging. Therefore, we created this article, taking into account the best practices that will save you a lot of time and frustration during the data acquisition. First we will share the min requirements for the flight plan.
Flight plan
For the Topography data product we require only visual (RGB) photos. A drone pilot will use an unmanned aerial system (a drone with a camera) to capture the data on site.
Visual (RGB) Data Requirements
GSD: up to 1.0 cm per pixel at ground level.
Front Overlap (direction of the flight lines): 75%.
If the terrain or the assets to be mapped are too complex, please increase the front overlap.Side Overlap (perpendicular to the direction of the flight lines): 70%.
If the terrain or the assets to be mapped are too complex, please increase the front overlap.Flight Path: At least 2 flight lines should be outside the boundaries of the operation in all directions.
Gimbal Orientation: standard Nadir (-90 deg).
If the terrain or the assets to be mapped are too complex, capture additional oblique photos to improve the quality of the end result.Image Format: JPEG.
Each image should contain the following metadata: GPS location, relative altitude and local timestamp.Image Quality: in focus, free from motion blur and with minimal glare.
At least 20 photos need to be uploaded to the Sitemark platform.
Accuracy
Flights requiring a high Absolute Accuracy in the region of 2-3cm in horizontal and 5cm in vertical need to be carried out utilising either a Real Time Kinematic (RTK) or Network RTK (NTRIP) solution. If neither of these are available, then Ground Control Points should be used.
Further information can be found in these articles:
Flights can also be carried out using a Post Processing Kinematic (PPK) solution. However, Sitemark does not post process drone data, therefore the post processing must be carried out by the Pilot before uploading the imagery to the platform.
The images should have the metadata amended to take into account the PPK corrections. If the images are not post processed, then the final dataset created from the imagery will not have high Absolute Accuracy.
Ground Control Points
Ground Control Points (GCPs) are optional if high Absolute accuracy is not required, but are still highly recommended. Even when using photos that have been geotagged using a Real Time Kinematic (RTK) or a Post Processing Kinematic (PPK) solution, we highly recommend placing at least one GCP for optimal position accuracy of the end result.
For more information on how to use Ground Control, please refer to the following article: How to Use Ground Control
Blocks
While we recommend flying sites in one continuous block there can be circumstances where it might be useful to use blocks either when flying or uploading.
For example, if there are large elevation differences that make it necessary to have multiple flights to keep your GSD consistent. Or if there are objects such as powerlines crossing the site that make it not safe to fly one altitude across the whole site. In these instances you will beed to fly separate flights so it would be a good idea to split the operations into blocks