I everyone I'm Vikshut. This is my colleague Arjun. Hello!
And today, we're at site.
We're going to demonstrate how to mark Ground Control Points, how to take measurements and then how to go about post-processing.
That's what we'll cover in the next lecture.
So today we are at a site in Mysore, a city in Karnataka, in India. And this site is approximately about
an acre. Now, the owner had a problem with measuring the site through satellite imagery because the satellite
imagery was quite inaccurate and wjat he required was a drone survey which was georeferenced
accurately and also on which he could do measurements.
He can get the contours and various other details.
So, we're going to show you all the steps involved in marking Ground Control Points.
So we're going to use a Trimble R8 GPS receiver. This is going to act as the rover in the site. And we have the base station
which has been being set up in a known location.
So what we need to do is mark ground control points strategically at different points in the site.
Now if you look at the site it's pretty much a square shaped site.
And what we need to do is in the four corners of the site, near the 4 corners we're going to mark ground control points
and one at the center.
So that's a total of 5 points that need to be marked. It's in the shape of the 5 on a die face.
If you see the 5 you have the 4 corners with the dots and one in the middle.
So, that's how we're going to mark the points. Let's show you how we do it. Here is a Trimple R8 receiver placed on a range pole
supported by a bipod. As mentioned earlier, we are capturing 5 GCPs for the site.
Here is the first GCP close to the center of the site.
The range pole is positioned at a point.
While this data capture is going on.
We use lime whitewash to mark an "X" at the point as demonstrated here.
Here you can see that the TSC2 survey controller capturing the coordinates of this point.
The point is name as "C" as in center.
And the data is captured on the controller.
If you observe the four corners from where we are standing you can see that this point has been marked
approximately at the center of the site.
So we complete the capture process for this point and move on to the next point.
Repeat the same for each of the 4 corner points.
For convenience we've named the points as "R1"
"L1"
"L2"
and "R2" where L represents left and R represents right.
You can clearly see that the flight plan is such that the corner GCPs are about 20 metres inside the
edges of the flight plan so that we can capture sufficient number of images for each of the corner
GCPs. We have explained in complete detail how to plan and execute a drone mission in part 1 of our course series.
The drone mission is then executed.
The drone covers the site in a preset grid capturing images all along the way with an overlap of 80
percent.
The captured points are downloaded and processed in our office on the Trimble Business Center and we
get the coordinates of each ground control point. The point coordinates are made available in the coordinate
system of your choice in an excel file.
As you can see here we have got the 3D coordinates of each of the points - C, R1, Ll, L2 and R2 in WGS84
/UTM Zone 43N coordinate system. In the next section,
we will get into the details of processing the drone image data and the GCP data in Pix4D.