The base had a few options for the setup which is: set "over a known point," or "over any point." I chose over any point. Made sure to get an accurate reading down to centimeter-accuracy. Turned on base station (Leica GS16) and rover (Leica GS18T). This is the workflow I followed during my test:Ģ) Arrived to field. In short, everything went smoothly until I imported the GPS points I captured with the Leica unit into Pix4D software and it was just miles off from the testing site. The gear I'm using is the Phantom 4 Pro V2 with the Leica GS18T rover with a base station and have some landing pad GCPs. Once a GSD is calculated, it’s used to guide the drone in flight.I recently got into drone mapping and invested a great deal in all the equipment needed. The lower the GSD, the better your accuracy when measuring surfaces of different elevations, keeping the difference between the real volume and the measured volume of a stockpile to a minimum. With lower GSD, anyone using the survey map can measure distances of objects on the ground to a highly accurate degree. For example, flying a drone over a large pit or tall stockpile affects the GSD and potentially the accuracy of the survey because of the different terrain heights. Elevation plays a key role in the accuracy of GSD. GSD helps in drone flight planning by directing surveyors on how high the drone should fly to capture photos and what camera settings to use, including sensor width, focal length, and image resolution. How ground sample distance improves drone surveying accuracy We would need much smaller squares to determine the bucket’s width accurately enough to correctly identify the loader. The bucket is more than one square wide, but less than two-a huge range as far as loader buckets go, so we can’t measure the bucket accurately enough with our squares. What are our accuracy requirements in the revised scenario? This time, we need accurate enough data to measure the bucket and identify the loader. Since the loader is much bigger than the squares we’re using to locate it, we can tell the operator to head to square F3, where they will easily find the loader to move it.īut what if they need to know how wide the bucket on the loader is, so they can send the correct operator to move it? Again, we can only use the squares on the board for measurement. What are our accuracy requirements? Well, we need accurate enough data to find the loader. We need to tell the supervisor where it is, so they can send someone to move the loader-but we can only use the squares on the board for measurement. Let’s say we have a (very) big chessboard, and someone has parked a front-end loader on it. Why is it important to calculate ground sample distance?ĭigital images are grids of colored squares (pixels), much like chess boards. However, since spatial resolution describes the dimensions of a pixel relative to any object in focus, the spatial resolution of objects across an image with variable surface relief can deviate from the calculated GSD in such a way that objects closer to the sensor have a higher resolution, and those farther away have less. When working with flat ground, the distance between sensor and ground is similar across the entire photo, meaning spatial resolution and GSD are relatively equal. Spatial resolution refers to the pixel size within an image with respect to some real world object or terrain feature in focus. This is normally represented by the altitude of the drone. GSD calculation considers the drone’s sensor properties and focal length (distance between sensor array and the camera lens), as well as the distance between the sensor and the ground when the photo is taken. What is the difference between ground sample distance and spatial resolution?Īs we discussed, GSD refers to the dimensions of a single pixel in an image, as measured on the ground.
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