If you know the coordinates, you can enter them in the boxes. Here I’ve already clicked on the corresponding point on the Toporama map, and the coordinates have been filled in. If you want to go through the exercise of manually adding reference points, delete the points file.) (If you’ve downloaded the MelancthonAerial archive from here, the georeferencing points should load automatically from the “Melancthon Aerial July 22 09.png.points” file. So I choose a pixel on the map in the georeferencer, and a dialogue comes up: These intersections are fairly well spaced apart, and are clear on both maps. Here are the ones I’m going to use: Point E-W Road N-S Road NoteĤ 15th Side Rd County Rd 124 just S of where 124 straightensĦ 4th Line 5th Line 4th Line really runs SE-NW I’ve chosen road intersections as my control points. You want to have the highest zoom that the map’s still clear, as the accuracy of your final map depends on how well you placed control points. ![]() If we open the raster, you can zoom into the area into which you want to put control points. Opening up the georeferencer plugin (which is now in the Raster menu, as of QGIS 1.8) gives you a whole lot of blank: Toporama uses EPSG 26917 in the area (easily checked with gdalinfo it’ll come up with something like AUTHORITY]), so you should set the project to use that CRS:Īnd here’s the raster map loaded into QGIS You want to set up your project so it uses the coordinate reference system (CRS) that the control point map uses. I’ve downloaded it as UTM, as it’s easier to measure distances that way. I’m going to use Toporama‘s digital image maps, as they’re clear and fairly accurate. GeoGratis has a bunch of good data sources, and they are free to use. You could always use Google Maps, but then you’re well down the derived work sinkhole. There are lots of sources of coordinates for your control points. ![]() One thing about georeferencing is that both the source image and the map from which you take you control points affect the licensing of the final map. It’s clearly derived from something like Google Maps, so it’s not exactly a free image I can throw about. NDACT has a helpful map (2.4 MB PNG image) had a helpful map (which I’ve kept here so you can work through this: MelancthonAerial), but it has no scale. I’ve heard from North Dufferin Agricultural & Community Taskforce (NDACT) that a large quarry is planned in my area. Scanned maps can sometimes be a little distorted, but QGIS’s georeferencer can handle that, within limits.įor an example, say I live in Redickville, ON (I don’t, but some folks do). The pixels could be from a scanned map or from a screen image. What that allows you to do is convert screen pixels to a map of an area. Quantum GIS (QGIS) has a very powerful image georeferencing module.
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