Check out our 6-minute overview video for a summary of this article
Ground Control Points are an effective way to increase the accuracy of a map (more about mapping accuracy here). To ensure that your GCPs process accurately and efficiently, it's imperative that DroneDeploy receives specific pieces of information for your project. Please review this guide prior to adding GCPs to a map.
GCPs that follow this guide should take 10-30 minutes to preprocess (Step 5) and 10-20 minutes to complete in-browser tagging (Step 6). Your GCP map will then immediately begin processing as normal.
However, GCPs with the following criteria will be easier and quicker to process
- Requests contain 10 GCPs or less
- Requests contain 1000 images or less
- GCP targets are unobstructed and clearly marked with an X or checkerboard larger than 4 sqft.
Need a Refresher on Projections, Reference Systems or Sea Level?
Check out this guide on the many intricacies related to global accuracy to help better understand and improve upon your map's accuracy.
Once you have selected your images (but before you start processing your map) select the GCP drop-down.
Download the GCP file template and add your coordinates to the template. The template will contain example coordinates for you as a guide. You can also upload your GCP data in a .csv file directly but it must follow our required formatting. For more information, please read our GCP .csv Checker Tool documentation.
Make sure you ask your GCP surveyor what EPSG they are using and request WGS84 (EPSG 4326) before GCPs are measured
If you are a drone service provider it's also important that you ask your client if they require mapping data in a specific EPSG code. You must have a valid EPSG code to use GCPs with DroneDeploy.
We cannot process maps that do not have an EPSG code
Unfortunately, if your GCPs are measured in a local or arbitrary coordinate system that is not listed in the EPSG Geodetic Parameter Registry, we cannot process them.
Enter your recorded GCP coordinates into the template or check that your GCP .csv follows the formatting shown in the template. Make sure your columns are Northing/Easting or Latitude/Longitude and please check that the values are not flipped the other way around when entering them into the template or we will not be able to process them. Also, make sure that your elevation units reflect the same units as your selected EPSG code. If you are using WGS84 your elevation should be in meters. If you are using a State Plane coordinate system your elevation will likely be in US survey feet.
This template document contains example coordinates. You can include your coordinates in State Plane or WGS84 Latitude / Longitude. Please make sure that the units of your coordinates match the units of the EPSG code.
Once you've added your GCP information to the template, save your .cvs it and then upload it into DroneDeploy.
Upload your completed GCP Excel File into DD as a .CSV file
Next, add your EPSG code. A full list of Codes can be found at Spatial Reference. Again, most GCP maps are in WGS84 or one of the NAD83 (typically not HARN, CSRS, or NAD27) State Plane Coordinate Systems.
Add your EPSG Code
Once you have finished the above steps, click "Add GCPs". You are now ready to start processing your images by clicking the "Upload Images" in bottom left corner of your screen.
DroneDeploy will begin pre-processing your GCP map. Once the pre-processing is complete you will receive an email that will take you to our in-browser GCP tagging tool.
Example of the email notifying you that your pre-processing is complete.
If your GCP .CSV was successfully read by out auto-tagging tool then this step will be skipped and you will proceed directly to step 4.
If we encountered a problem with your .CSV or EPSG code, you will need to fix this data using our GCP .CSV Checker Tool. Please see our GCP .csv Checker Tool documentation for a full walkthrough of this process.
Here is what the GCP .CSV Checker Tool will look like in your browser.
Once your GCP .csv has been accepted, you can start selecting each GCP point. To do this select the GCP you would like to start with and use the in-browser user interface to locate the GCP target.
Once you have located and tagged the correct GCP target. You will be prompted to carry out a secondary refinement to make sure the exact pixel is selected. This is important to ensure the highest accuracy is achieved within the map. There will be up to 8 images validate in the secondary refinement stage. It is important to complete all of them to achieve the highest accuracy within the map. If for some reason one of the markers is undetectable during the refinement you can exclude the marker by unchecking the blue square in the top right corner of the image.
Because the new workflow allows the user to tie in their own GCPs, you can now use non-conventional targets within your map. This makes it much easier to show up to a site and utilize well-known features as targets rather than conventional targets.
Because sites change frequently, sometimes a target will no longer be visible on an active project. If you need to skip a GCP you can do so by clicking on the "Skip GCP" in the upper right-hand corner during the initial workflow of finding the target within the map. This can greatly improve the accuracy of the overall map once it has been processed with GCPs.
Once you have tied in all of the markers on the map you can click Preview in the top right corner. This will preview how many tie points each marker selected has within the map. It is not recommended to use markers that have less than 3 tie points. If you do have a map that has multiple markers with 4 tie points or less it is recommended to increase overlap and altitude within the area of interest being flown.
Once you have validated the tie points, press submit. That's it! You're done! You will receive an email once your map has completed the final steps to increase the accuracy of the map on our servers. Give yourself a high five. Beter yet high five one of your co-workers. This stuff gets complicated quickly and you just nailed it :)
Once your map has been completed, we will send you an email with a link to your map. You can generate an accuracy report of the finished map using the Accuracy Report App that is available in our App Marketplace. The map will be available on your account dashboard on DroneDeploy.com.