Accuracy can refer to different characteristics in a data set.
Vertical Accuracy
Ground control is highly beneficial, but not required.
When client-supplied ground control is available, it is possible to measure the vertical accuracy of a survey. With a single ground control point (GCP), we can align the survey vertically (z). When more GCPs are available, we can perform additional refinements.
The Survey Project Report will include an accuracy statement. If enough suitable ground control points were supplied, your Survey Project Report will also include the vertical accuracy, including the root mean square error (RMSE) and the linear error 90% (LE90).
Some factors that influence survey accuracy include:
Availability of client-supplied ground control
Quality and distribution of client-supplied ground control
Ground control makes it possible to measure and improve the horizontal accuracy of a survey. With a single GCP, we can align the survey horizontally (x,y). When more GCPs are available, we can confirm the geolocation of the survey and perform additional refinements.
Relative Vertical Accuracy
Surveys produced from WorldView satellite imagery have a relative accuracy of ~20 cm over 5 km, independent of ground control.
High relative accuracy is particularly important for calculating volume changes in leach pads, stockpiles, waste dumps, and tailings facilities.
Accuracy Studies
The satellite used to acquire satellite imagery is one of the factors that influences the accuracy of an elevation survey or map (DEM).
Since 2004, PhotoSat has conducted dozens of accuracy studies to demonstrate the capabilities of commercial satellites for producing high-quality topography.
Ground control makes it possible to measure vertical accuracy and perform additional refinements to a survey (DEM).
Existing Data as Ground Control
Many types of data can be used as ground control.
These include:
High-quality ground surveys
Airborne or drone LiDAR data
Seismic source and receiver locations
Ground Control Scenarios
There are four possible scenarios:
I. Use Photo-Identifiable Features
If satellite imagery already exists (i.e. archive satellite photos), we can examine the imagery and suggest photo-identifiable features to be surveyed as ground control.
II. Lay Targets before Satellite Tasking
If we plan to acquire new satellite imagery, we can delay tasking the satellite so that clients can lay new ground targets. We can provide guidelines for constructing ground targets and advice on suitable locations for targets.
III. Proceed without Ground Control
We can obtain satellite imagery and produce the survey without any ground control. Although it will not be possible to measure vertical accuracy, the relative accuracy of each survey will not be affected.
IV. Reissue Survey
If new ground control becomes available after we have produced and delivered a survey, we can reissue the survey at a later date using the new ground control. Reissue fees may apply.
