Photogrammetry for Agriculture & Forestry
The photogrammetry is accessible from the home page: click on the analytic button, then on “Photogrammetry” and “Launch”:
Processing options
The default photogrammetry settings are displayed:
Type “Change Settings” if you need to modify the options:
-
Self-Service (by default)
- Selection of engine to be used resulting in quicker processing time and more control on the process
- Users will have the responsibility for identifying and clicking the GCPs if applicable.
- There will be no manual check of the photogrammetry outputs by Alteia
- Alteia recommend using this option by default
-
Advanced
- Takes more time than the self service since the photogrammetry outputs are checked by Alteia.
- Should be used in specific situations following Alteia recommendations
- Processing engine: for Agriculture and Forestry Alteia accounts, the photogrammetry engine selected by default is Pix4D.
- Depending on the sensor model, custom settings can be suggested by Alteia.
Please refer to the table about supported sensors and settings for agriculture in this article
Processing area: select none by default
The outputs that will be provided by default by the photogrammetry process are also displayed.
For multispectral camera, you can select additional vegetation indices.
- The outputs provided by default depend on the sensor model.
- You can add a suffix to the outputs if needed (optional).
Photogrammetry CRS
By default a CRS is proposed for the photogrammetry (applied to the outputs). You can change it if needed.
Reflectance Calibration
If the calibration needs to be processed manually, click on “Manual radiometry of the calibration target”
Cases where it is necessary to manually calibrate the reflectance:
- The automated calibration failed during the first try (see the article How to verify the calibration of the reflectance)
- The calibration target is an old model (ref <RP04 for Micasence)
- Following Alteia Support recommendation
In the next window you will have to select the calibration target within the data set, draw a polygon in the reflectance area and fill the albedo value for each band.
The albedo value is provided with the reflectance target by the manufacturer.
You have placed GCPs?
If you have placed and measured GCPs before the flight, click on the “GCP” button and drag and drop your GCP file.
The file should be in .CSV or .TXT format, no header row and only delimited with a comma. The file must contains the following columns in this order:
- name/reference of the GCP
- X coordinate
- Y coordinate
- Z value
- X accuracy (optional)
- Y accuracy (optional)
Once the GCP file has been uploaded, verify that the x/y/z columns appear in the correct order.
Select the GCPs coordinate reference system and then click on “Confirm”.
The GCPs should appear on the map as orange dots within the survey boundary.
- If nothing appears, then it may be possible that the CRS is incorrect or the X and Y coordinates are reversed.
- To retry, click on “details” to modify the file or CRS.
Once the GCPs appear correctly on the map you can go to the next step.
GCP Tagging
1. Click on “Start Tagging”
2. To tag the first GCP click on “Tag”
3. Select the images that you want to tag around that GCP. Please note that for multispectral sensor an “image” here is a set of different bands
- The GCP has to be visible on the image
- We recommend to tag at least 5 images around the GCP
- Select the most distante images from the GCP
4. Click on “Tag GCP”
5. On the first image click on the middle of the GCP with the pointer. Repeat the same operation for each band (multispectral sensor).
Repeat the same operation for each instance (image/set of bands) of that GCP.
Then click on “Done” and “Back”. On the dashboard you can see that all the images have been tagged around the GCP 1:
6. Repeat the same operation for all GCPs.
Once the GCP tagging is complete for all GCPs, click again on “back” and then “Launch mapping”.
Check of the reflectance calibration process (multispectral):
See the article How to verify the calibration of the reflectance
