When uploading preprocessed data, the number of credits consumed is based on the number of GigaPixels (GP) in your upload. Both the pixel size for the digital elevation model (DEM) and orthomosaic is calculated. The bigger of the two is used to determine the total Pixels.
The number of pixels in an image is hard to visualize or answer the question, “How big of an area is 4 GP?” To answer this question depends on the ground sampling distance (GSD) of either the orthomosaic or DEM you intend to capture. The ground sampling distance represents the physical size of each pixel in an image. For example, if you have a ground sampling distance of 0.1 meters, each pixel in your image is 0.1 meters by 0.1 meters in dimensions (assuming they are square pixels). The standard upload limit per credit is 4 GP which is equal to 4 x109 Px (4 billion pixels).
So how large is 4 GP in terms of a physical size?
- Let's take the example above where we have a GSD of 0.1 meters, i.e. each pixel is 0.1 x 0.1 meters in size. The area of each pixel is 0.01 square meters.
- Assume that the physical area you are interested in is perfectly rectangular and both sides of the rectangle align with the X and Y axes of the final map (the Easting and Northing). This means that there is no blank space in the image.
- Calculate the area by multiplying the total number of pixels covered in the standard limit—4 GP, which equals 4 X 109 Px (4 billion pixels) multiplied by the pixel area.
4 x109 (4 gigapixels) * 0.01 m2 = 40,000,000 m2 = 4000 Hectares
Dead space (commonly called nodata) is used in the calculation
When calculating the total pixels in a BYOD upload, the size of the entire image is used and not just the area containing useful data. This is due to how images are generated and stored. This can be illustrated by Figure (A) below. Here, you can see that much of the image contains no data or “dead space.” When the total number of pixels is calculated, the bounding box around the image is used.
For long and skinny areas not aligned closely with the X or Y axes, this can cause uploads to become very large even though they may not contain large amounts of useful information. If this is the case, consider splitting the image into smaller pieces to reduce the number of credits you consume. For example, you can see Figure (A) contains twice as much data as Figure (B) even though they contain the same useful information. Please note that only one DEM and orthomosaic can be used in each BYOD upload.
If you need to upload a pre-processed dataset in multiple segments, you can merge your data using the Composite Survey feature within the portal, just as you would with a standard survey dataset. For more information on composite surveys, please see our article on Getting Started with Composite Surveys.
I still can't do it!
We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.
If you're stuck, you can connect with our support team by clicking the support button on the top right corner of your user portal.