This article covers all the process of marking GCP's on images. This is needed for all flight instances that were marked as needing manual GCP's at upload time. After the upload and the the link process are done, the site will appear as “Pending GCP Marking” in the site map screen left banner as shown in the figure below.
The next step here
would be to open the flight by clicking on the "Pending GCP Marking" right on the site tab shown above or by opening the site and then opening the flight instance.
In all cases, it is
possible to start marking GCP in images.
The recommendation is to mark only 3 points on two images each (or 3 images each when using local coordinate system), and then
check accuracy. This will drastically improve
the location of the hints. When hints
are found the list on the left shows the number of images in which the hints
were found as shown below.
In this condition you may use the GCP manual moving option available to align the GCP’s with the images. This will improve the close-by image prediction for each GCP, hence it will speed up the GCP marking process. Below is a detailed explanation of all the alignment possibilities.
- Align the most northern GCP with the most northern image- Align the most southern GCP with the most southern image- Align the most western GCP with the most western image- Align the most eastern GCP with the most eastern image- Align the center point of all GCP's with the center point of all images
Using the Settings tool on the top right, set the major step and minor step of the manual movement.Use the single arrow ( ) to move the GCP's by the minor stepUse the double arrow ( ) to move the GCP's by the major step
Rotate the GCP's clockwise ( ) by X degreesRotate the GCP's counter-clockwise ( ) by X degrees
To mark a GCP on
images, you can click on it on the map or in the list. Clicking on a GCP will show the screen
Even if there were
no hints, the system shows close by images on the right side, and shows the
closest images in X, Y coordinates on the main view. To mark the selected GCP in the first image,
simply zoom in to find the mark and mark it very precisely in the center of the
mark with a left mouse click.
Repeat the process
on another image, by selecting it from the images on the right side. It is recommended to select an image that is
far from the first one. Once you mark
the point in two images click on the “Update Marking” button on the bottom
right. This will take you back to the
map screen showing you a list of GCP’s that were marked, and a list of GCP’s
that are still without marking as shown below.
Repeat the marking
process for two additional GCP's. Which
will bring you to the screen below. It
is always possible to show or hide information by selects or unselecting it from
the legend on the top right.
Additionally, it is possible to hide or show the whole legend as needed.
You may also here mark any of the GCP's as check points by checking the available CheckPoint check box next to it. Please refer to the Using Check Points article for full details.
Once done, the screen
below appears showing the accuracy of the GCP marks in meters (or the flight
unit if different), and in pixels for each image. It also changes the color of
GCP's that were marked to yellow on the map giving a clear indication of what is
marked and what is not.
To continue marking
the rest of the GCP’s, click on “Mark additional GCP” to show the list of GCP's
that were not marked yet. In the GCP's
Marking accuracy list it will show the GCP Name, the number (#Images) of images
in which the GCP can be marked in; hence images with hints, the number of
images (#Marks) the GCP was marked in, the marking residual in distance (Diff),
and the marking Residual in X, Y, and Z (Res. E, N, H)).
While the list of GCP's without marking shows
the Name of the GCP and the number of images with hints.
It is possible at
this point to start marking GCPs in more images by selecting the GCP from
either list or from the map. To mark a GCP
click on it in the list or on the map and mark it in at least four images that
are well distributed. Once done marking,
press the “Update Marking” on the bottom right to save marking and go back to
the prior screen.
At this point, you
need to mark as many GCP's as you want.
Once done marking as shown below, press the “Revalidate Accuracy” button
and wait for new accuracy residuals. If
residuals are high, check your markings to make sure you marked the correct
places. Adjust and revalidate until you
get good residuals. Then move to the
final step of generating the model.
At any time you may
turn on or off GCP display layers as shown below to help you better visualize