- Open a nadir photo (the camera pointing straight down). You can also drop it on the page.
- Control points: click a feature you can also find on a map, such as a building corner, jetty end or road marking, and paste its coordinates. Two points are enough. A third or later point shows how accurate the fit is (residuals). Spread the points out as far as you can.
- Query: after calibration, click any spot to get its latitude/longitude. You can copy it or open it in Google Maps. The status bar shows live coordinates under the cursor. To go the other way, type a coordinate into Find to mark where it is in the image.
- Labels: click a location, then enter a name and pick a colour. Drag the label body to move it. The pointer stays attached to the location, and you can drag the dot at its tip to move the location itself.
- Measure: after calibration, click points along a route. The hint shows the running total and the current segment. To finish, double-click or press Enter. Each measurement is kept with a length label, and clicking it shows each segment and its compass bearing. In Measure mode you can drag the points to adjust a measurement.
- Locate me: on a phone or laptop with location, shows your live position as a blue dot. The circle around it shows how accurate the position is. If you are outside the photo, the chip at the top right says how far away you are and in which direction.
- Map: after calibration, shows OpenStreetMap roads, paths, buildings and water over the photo. It's also a quick way to check the calibration. Use the arrow next to the button to choose layers, adjust opacity, or include the map in the exported JPEG. The first load for a new place can take up to a minute; after that it is cached.
- Areas: click to place corners. To finish, click the first corner, double-click, or press Enter. Backspace removes the last corner and Esc cancels. Then name the area and pick a colour. Once the image is calibrated, click the area or its label to see its size in m² and ha, and its perimeter. In Area mode you can drag corners to reshape an area, drag the small midpoint handles to add a corner, and Alt-click a corner to delete it.
Drone data
Photos straight from a DJI drone record where the drone was, how high it flew and which way the camera pointed. If a photo has all of this and looks unedited, Nadir uses it for an approximate calibration (roughly ±10 m) as soon as the photo opens. Your first control point then fixes the position exactly, and with two or more, control points take over completely. Editing software may drop these details, and cropping or stitching makes them unusable. In that case the drone's GPS position is still shown, with a map link, to help you find control points.
Transform models
- Similarity (≥2 points): scale, rotation and shift. This is the right model for a true nadir shot over roughly flat ground.
- Affine (≥3): also allows unequal scale and shear.
- Projective (≥4): corrects a slightly tilted camera. Needs well-spread points.
Accuracy depends mostly on your control points. A nadir image is only truly to scale on flat ground, and rooftops and treetops shift slightly outwards from the image centre.
Shortcuts
P/Esc pan · C control point · Q query · L label · A area · M measure · +/− zoom · 0 fit · scroll wheel zooms · drag to pan in any mode.
Sharing
Share saves the image with its control points, labels, areas and measurements to My projects in your account, and gives you two links. You need a free account for this; logging in is only needed to save and share.
- View link: recipients can explore, query and add their own labels. Their changes stay in their own browser, and they can revert to the shared version at any time.
- Edit link: changes are saved back automatically for everyone. Keep this link to yourself and trusted collaborators.
Your work is autosaved in this browser for each image, and Project → Save exports it as a file.