How to Georeference a Map (PDF/JPEG) in QGIS

hello guys welcome to another tutorial in this tutorial i'm going to show you how to georeference a jpeg or even a pdf quickly just in a matter of few minutes using qgis now just to highlight the importance of this i'm going to demonstrate the steps of this tutorial through a practical application over here i have logged into this citywalks dot info website and over here you can actually get a pdf map of the top 10 attractions of london now let's say that if you're interested in creating a shape file just in a matter of few minutes of these different spots that you can see over here which are marked in different stars let's say you would like to create a shape file of these 10 spots which are regarded as the top 10 attractions in london it would be quite handy if you had this map let's say on qgis or in a gis software like like qgis so that you can simply create a shape file and usually just put the dots on top of these tasks which you can later on convert into into a separate shapefile of points now that's exactly what i'm going to do so first of all i'm going to first download this pdf as you can see it's actually a pdf of quite a high resolution now i can use this save button in order to save this pdf and now as you can see over here i have already saved that pdf into one of my folders all right now if you're trying to jio reference you don't actually have to necessarily convert this into a jpeg you can actually georeference this while the file is in while the file is still in pdf format so that's what i'm going to demonstrate to you guys today so let's go ahead and open up qgis and for this i'm going to use one of the base layers now now if you have been following our tutorials for quite some time you might know that we use open street maps quite frequently since i have already installed this quick map services plugin i can directly go to web and go to osm and import this osm standard which is the standard openstreetmap now in case if you haven't installed this plugin you can simply go to plugins manage and install plugins and simply search for quick map services and the installation process is quite straightforward so i'm not going to run through that at this particular moment so now we have a properly referenced base layer which is the straight map all right now what i'm going to do is i'm going to this raster option and over here there's one module called georeferencer now in the previous versions of qgis actually this used to be an external plug-in but somehow they have incorporated this into this latest later versions of qj especially the recent versions of qjs3 so that's quite handy we can directly go ahead and open this up and from here we can actually load our pdf directly into this reference window you can do that simply by clicking over here open raster and if you navigate to the place where you have saved your pdf you will see that it's actually recognized as a as a valid file format so i'm going to open this and now you can see that by using your scroll wheel you can actually zoom in and out and even just pan it pan it around using your mouse wheel and now over here in the lower lower left side you can see that there is one option called gcp table which is basically an empty table as per now this gcp stands for ground control points so what we are going to do is we are going to provide the coordinates of points which we can accurately identify on this open straight map as reference points to enable the process of geo referencing now since i know that this is somewhere over over this waterloo bridge i can simply zoom into the city of london until i can sufficiently identify where exactly this area is and over here you can see that the waterloo bridge is over here so what we have to do is first we have to specify a point on this map and after that we have to provide the corresponding coordinates of the same exact point from this open straight map now just by panning the map around what i'm trying to do is i'm trying i'm just trying to identify a common common location or a common landmark let's say now just to start the process i'm going to go with this point so what i'm going to do is i'm going to actually zoom into this point sufficiently so that i can accurately pinpoint to the to this corner and now it says that you have to provide the x and y coordinates now you don't really have to provide it manually you can provide it from the map canvas directly so you can so just go ahead and click on this button and then you can see that it disappeared and all you have to do is just click on the same exact point on your openstreetmap and the corresponding coordinates will be extracted just like this and when you click ok you can see that one set of points got included into this gcp table now generally it's recommended to use about five to six points with sufficient special distribution in order for the geo referencing process to happen with a sufficient accuracy so that's what we are going to do now let's say we for the for the second point let's go to somewhere over here close to this tower bridge yeah maybe as the second point what i'm going to do is i'm going to go with one of these corners of this bridge pierce of the tower bridge now as you can see over here from the jpeg it's not that clear because when i zoom in i start seeing the pixels but but for the demonstration purposes i think this is this should be sufficient enough and i'm going to pick that point from the map canvas which which is actually actually going to be this point yeah now you can see that we added two points now let's go ahead and try to have try to pick a point from somewhere else a bit further from the from the from the from the location where we actually did our initial geo referencing now let's try to pick a point from somewhere over here just to make sure that we're actually allowing a sufficient spatial distribution i see a road like an arch over here so i'm going to maybe go ahead and pick this point and from the map canvas i'm also going to pick that point all right we took three points already let's see if we can find something from this buckingham palace garden area yeah maybe i think i might be able to hit this point which is actually this point right here and let's go with one just one more point maybe i can go to the eastern side again and let's say that we go with this crossing point right here and i'm going to pick that point from here as well all right now we have about five points i think this should be sufficient enough but you can always tweak in case if finally when you do the geo-referencing and if you find that the map has not been geo-referenced properly you can always actually come back and maybe increase the number of points or if you do have any points which you are not really sure about you can actually get rid of those points so once you have done that you can simply go ahead and click on the start geo referencing triangle button in order for the geo referencing process to begin so let's go ahead and click on this and as soon as you click on this button you will get a dialog box like this in which you will be actually able to select the transformation type and the resampling method and also set the corresponding coordinate reference system now there are different transformation types and one can actually differ from the other depending on the algorithms that they use now for this i'm going to go with this linear transformation type and the resampling method also i'm going to go with the default one which is the nearest neighbor and the target coordinate reference system i'm going to use the same coordinate reference system uh which this open street map player was in which was uh epsg 3857 wgs 1984 pseudo-mercator projection and over here you can specify a name for the output raster i'm going to name this one as london attractions map georeferenced and the compression type i'm going to leave it as none and of course after you are done with this you would like to load the layer into qgis so you can go ahead and put a tick over here and after that you can click ok and finally for the process to begin you can simply click on this button again now you can just go ahead and close this and i'm going to save the gcp points just in case and over here now you can see that that pdf has been exported into a geotiff which is now a raster which is actually fully geo-referenced as you can see from here you can see that the river actually fits quite nicely over here to this base map and even this pond the serpentine pond actually also fits quite well and if i navigate back to the place where i have saved where i exported this file into this is actually the geo-referenced file the t-file now in case if you would like to just drag this one and drop it over here and see whether it actually properly got geo-referenced or not now let's go ahead and remove this one and i'm going to maybe create a new folder and what i'm going to do is i'm going to cut this and put it over here and now you can see that this file by itself is actually just a standalone file so if it was properly geo-referenced then when i drag it and drop it over here it should perfectly fit into the existing base layer just like this and you can see that it's actually a near perfect match now i do have another base map which is google which is a google satellite map what i can do is i can simply maybe turn off this open street maps layer and i can import this google satellites layer and see whether it actually fits correctly or not just to just as a further check let me go ahead and push this layer on top of this and from here you can see that it's still fitting quite well from over here as well and one another way that you can do a quick check is simply by going to this raster layer and you can adjust the transparency just like this maybe if i reduce the transparency to be about 66 percent or maybe just a bit more yeah now you can see that it's almost a near perfect fit as we can see over here and now coming back to our initial objective let me go ahead and revert this back to 100 yeah coming back to our initial objective if someone wanted to get a shapefile which consists of let's say these points which are considered as the top most 10 attractions in london all you have to do is just go to your corresponding folder and you can go to right click and go to new shape file and from here maybe i can give a name to the shapefile attractions london and i'm going to select the geometry type to be point and the coordinate reference system i'm going to use the same coordinate reference system which is the existing one and after that i can go back here and simply drag this one into my working space and over here you can go ahead and right click and toggle the editing mode and from here now all you have to do is just go over here and maybe select the corresponding point and give the corresponding id number accordingly the reason why we can do this like this is because now our base layer is actually a correctly geo-referenced base layer so that's the the advantage of having a properly geo-referenced base layer like this and finally i can conclude the process by entering 6 for this point i guess i covered all all the 10 points and after that and you can simply turn this editing mode off and you can save the edits like this and now even if i deselect this and maybe if i go ahead and change the settings change the appearance of this of these points let me go ahead and increase the size and also i can add the labels now quite easily just like this i'm going to specify the labels in yellow color just like that yeah now you can see that we already created the shape file and even if you go back to your working folder you can see that the set of shape files the set of files which corresponds to the particular shapefile attractions london it's just right over here so that you can simply pass it on to someone else if you if you wish to well this was actually an additional part just to just to demonstrate to you guys what could be a potential uh usage of actually doing this kind of a geo-referencing exercise so i guess this was a useful tutorial for you guys and if you did like the tutorial you know exactly what to do show your support by hitting that thumbs up button and you can even consider subscribing to our channel if you do like to see these kinds of tutorials in the days to come as well so i'll see you guys in the next one

Channel: GeoDelta Labs

Views: 35,268

Rating: 4.9499998 out of 5

Keywords: how to georeference an image in qgis, georeference qgis, georeferensi qgis, georeferencing a map, qgis tutorial, georeferenced map, create a map, scanned map, scane a amap, Georeference, Georeferencing, geo reference, geo referencing, geo-reference, GIS, QGIS, Georeference in QGIS, toposheet, referecing using QGIS, reference, how to georeference, create georeference in QGIS, mapping, geospatial, cartography, georeference, crs, raster, QGIS3, gereffing, plugin, GCP, ground control point

Id: jKLBFddpTGI

Length: 13min 39sec (819 seconds)

Published: Sat Sep 19 2020