Ground Control Points (GCPs) are visual markers on the ground with known coordinates that increase the orthomosaic accuracy and help maintain alignment of multiple surveys. Ground Control Points (GCPs) in other words, are reference points provided by you to improve the positional accuracy of the orthomosaic.


There are two ways to add GCPs,

  • By adding them Manually
  • By importing a separate file from your machine


To add GCPs follow these steps.
1. Open PrecisionViewer.

2. On the survey thumbnail, click Eye icon to display the Infield View of your survey 
     (Figure 1 and Figure 2
). 

Figure 1: Eye icon on the survey thumbnail



Figure 2: The Infield View


3. Select GCP (Figure 3).

Figure 3: Selecting Ground Control Points (GCP) option


4. Click Add Ground Control Points.


Note: You can either add GCPs by uploading a file from your drive or 
                 you can mark them manually.

                   You must provide at least three GCP points and for each GCP point, you need to 

                 tag minimum three images. The addition of more than three images will lead to 

                 improvement in survey accuracy.




Adding GCP Manually


To manually mark GCPs follow these steps


1. Select Manual Entry after clicking Add Ground Control Points (Figure 4). A New GCP window pops up.

Figure 4: Selecting Manual Entry


2. Select either 2D GCP or 3D GCP in the drop-down box.

3. Place the pointer on the appropriate point on Google Map and click Save (Figure 5).

Figure 5: Pointer placed on Google Map



4. Select an image from the Candidate Images list and mark your selected GCP position.
     Repeat the procedure to tag next two candidate images (Figure 6).

Note: Candidate Images are the images containing your selected GCP's geo-referenced 

                (GPS) parameters (Latitude, longitude, altitude).

Figure 6: First GCP tagging on a candidate image



5. After tagging the third candidate image, you have completed adding your first GCP (Figure 7).

Figure 7: Tagged images for the first GCP



6. Click Cancel and repeat the above procedure to add two more GCPs (Figure 8).

Figure 8: Marked GCP




Adding GCP Using a Separate File


To upload GCPs through a separate file follow these steps.


1. Select Import GCPs in New GCP drop-down list.

2. Choose the appropriate file from your computer.