DroneDeploy

GCP Request Checklist

Need a Refresher on Projections, Reference Systems, or EPSG codes?

Check out this guide on the many intricacies related to global accuracy to help better understand and improve upon your map's accuracy.

Please review this list before submitting a GCP request.

1. Do you have the correct EPSG code?

2. Do you have at least 4 GCPs measured with high precision GPS?

3. Are all your GCPs clearly marked, unobstructed, and visible in at least 4 images?

4. Are your GCPs at least 50ft from the edges of your map?

5. Do your CSV column headings and units match your EPSG code?

6. Does your CSV follow the prescribed template?

If you have met these requirements you are ready to add GCPs to your map. Check out our step by step guide for details on the in-browser GCP workflow.

Please Note, GCPs maps that meet these additional conditions will process in the fastest time possible!

  • GCP locations are measured in WGS84 (EPSG Code: 4326)
  • Requests containing 10 GCPs or less
  • Requests containing 1000 images or less
  • GCPs are unobstructed and clearly marked with an X or checkerboard larger than 4 sqft.

If you are unsure if you meet a specific requirement, we have gone into more detail about each point below

You can also find more information about these requirements in our 6-minute GCP overview video

1. Do you have the correct EPSG code?

To successfully process a GCP map you must have the exact EPSG code that was used to measure your GCPs. If the EPSG code you submit is different than the one used to record your GCPs we will be unable to process your map. Here's an overview of EPSG code to get a better idea of what's going on.

An EPSG code is a standardized definition of the spatial reference system used by your map. The code tells us 3 things:
1) The Coordinate System (ie. where to place the origin, or geodetic datum)
2) The Measurement Units (ie. Feet or Meters, Northing/Easting or Lat/Long)
3) The Map Projection (The earth is a sphere but maps are flat! We use map projects to convert between the two)

WGS84
DroneDeploy strongly recommends using WGS84 for GCP projects as processing time will be greatly reduced. WGS84 (EPSG: 4326) is the standard that our GPS and GNSS networks operate on. WGS84 uses Lat/Long, measures elevation in meters, and uses an ellipsoid coordinate system with no projection. More information on WGS84 and mean sea level here.

State Plane Coordinate System
Other common EPSG codes are from the State Plane Coordinate System. SPCS is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county lines. These are all based on the North American Datum of 1983 (called NAD83). NAD83 uses Northing/Easting and measures elevation in US survey feet but depending on the specific state plane it can use many difference coordinate systems and map projections.ent for standard surveying techniques can be found here.

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.

Make sure you ask your GCP surveyor what EPSG they are using to measure your GCPs and request WGS84 (EPSG 4326) before measurements are recorded

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.

2. Do you have at least 4 GCPs measured with high precision GPS?

DroneDeploy requires a minimum of 4 GCPs for processing. In our experience, 5 GCP work great and very rarely are more than 10 needed, even for particularly larger maps. Please note that if you decide to use more than 10 GCPs, processing time for your map will increase. Again, make sure your GCPs are at least 50 ft from the boundary of your map.

As shown below, your GCP much be measured with precision GPS. These generally come in 2 different types: RTK and PPK.

RTK, or Real Time Kinematic, GPS is a technique used to enhance the precision of position data derived from satellite-based positioning systems. It requires a static base station linked by radio to a mobile unit used to measure each GCP location. An example is the Trimble R8, pictured below but recently low-cost alternatives like the Emlid Reach have entered the market.

Measuring GPS from the center of the point helps increase accuracy.

Measuring GPS from the center of the point helps increase accuracy.

PPK, or Post Processing Kinematic, GPS uses similar technology but the static base station information is coming from a know correction network. Most products use the Continuously Operating Reference Station (CORS) Network provided for free by the National Geodetic Survey.

3. Are your GCPs clearly marked and unobstructed?

A quality GCP can be as simple as two intersecting lines. The goal is to create a visible feature on the area that is being flown. Because flying altitudes are generally from 250-400 ft (about 75 to 120 meters), the GCP needs to be clearly visible in as many images as possible. Each GCP must be visible in at least 4 images or we cannot include it.

Adding a center mark to the GCP, as seen in the images below, eliminates confusion as to where the GPS measurement was taken.

Example of a well constructed GCP. The marker is large enough that it is visible from far away, but the location will be measured from the center to increase accuracy.

Example of a well constructed GCP. The marker is large enough that it is visible from far away, but the location will be measured from the center to increase accuracy.

If you cannot mark your GCPs with paint there are a variety of low-cost ways to make excellent markers with items from the internet or home depot. These sheets of roofing rubber($4.66 each) with these vinyl stickers($1 per 6" x 12" sheet) can be used to make a simple checker pattern but they need to be staked into the ground if its windy.

These rubber and vinyl markers end up costing $5 each and are extremely weather resistant.

These rubber and vinyl markers end up costing $5 each and are extremely weather resistant.

A fantastic DIY approach we have seen is a 12" bucket lid stuck on a white plastic 14x14 access panel from Home Depot

A fantastic DIY approach we have seen is a 12" bucket lid stuck on a white plastic 14x14 access panel from Home Depot

It's important to note that event with quality GCP markers, you markers must be clearly visible from your flight altitude to be successfully processed. Visual obstructions like overhangs, snow, shade or glare can make your GCPs difficult to identify in your map photos.

In this example, one of the GCPs is in a heavily shaded area and nearly invisible in the map photos.

In this example, one of the GCPs is in a heavily shaded area and nearly invisible in the map photos.

4. Are your GCPs at least 50ft from the edges of your map?

We highly recommend leaving a 50ft buffet between your GCP and the boundaries of your map. This is because if your GCP falls outside the map boundaries, even by 1 foot, we cannot process it. What a waste! Our recommended GCP placement strategy is to use 4 GCPs located in the 4 corners of your map on relatively flat surfaces with one more the center as shown below. Again, DroneDeploy requires a minimum of 4 GCPs for processing. In our experience, 5 GCP work great and very rarely are more than 10 needed, even for particularly larger maps.

In this example, the subjects of interest are the 2 star shaped buildings so we place our GCP as best we can in the corners and center.

In this example, the subjects of interest are the 2 star shaped buildings so we place our GCP as best we can in the corners and center.

In the example the subject of interest is not a square so we distribute the points as best we can in the corners and center. You can also see some other measurement annotations.

In the example the subject of interest is not a square so we distribute the points as best we can in the corners and center. You can also see some other measurement annotations.

5. Do your CSV headings and units match your EPSG code?

If your GCPs were measured using WGS84 (EPSG: 4326) then your column headers must read: GCP, Latitude, Longitude, Elevation (m). This is because measurements in WGS84 use lat/long and meters for elevation. Please make sure your data is not listed as Longitude, Latitude or everything will be flipped!

If your GCPs were measured using NAD83 / California zone 3 (EPSG: 2227) then your column headers must read: GCP, Northing, Easting, Elevation (ft). This is because measurements in NAD83 use Northing/
Easting and US survey feet for elevation. Again, please make sure your data is not listed as Easting, Northing or everything will be flipped!

6. Does your CSV follow the prescribed template?

Please make sure you do not alter the template in any way and make sure your file is saved using a .csv file extension. If you follow the instruction listed in the previous section you should be good to go.

GCP Request Checklist