Georeferencing an Image in ArcGIS Pro

all right so one of your homeworks deals with geo referencing images and so these are maps or images that maybe you've scanned in or maybe it's an aerial photo that needs to be geo-referenced it needs to have that spatial reference information and so this is one way to do that using ArcGIS pro and so I just wanted to show you a couple of tips and tricks that have helped me in the past so here we're looking at an old black-and-white aerial photo this is a shy rushlight in west central Illinois and so we're going to go ahead and add the scanned in map that we want to georeference and so here we've got this scanned in JPEG and I'm gonna add it okay and you see that that JPEG got added but we don't see it anywhere and I can right click and zoom to later and there's the map there's the map that we want to scan in but obviously it's not where it needs to be it doesn't have spatial reference information and so it's just being plotted at 0 0 and so if we zoom out since this is in UTM 0 0 is down here by Central America and obviously that's not where it belongs so we need to georeference it so I'm going to right-click on the aerial photo and go zoom to layer now this aerial photo is properly geo-referenced and you can see based upon the base map that this aerial photo is right where it needs to be so here's the base map and our GIS and if you follow this road you see that Road just shows up perfectly just like you would expect so we can use this aerial photo to geo locate the scanned in mouth so the first thing we want to do is we want to kind of zoom in and get pretty close to the area that's shown on the scanned in map and so that's the the lake down here now here's a shortcut that I suggest you you get comfortable using when we need to pan a map so I'm trying to zoom around but I need to shift to this map a little bit you know we have the tool that allows us to do that and so we can just click and grab in our GIS pro but sometimes we're using a different tool that won't allow us to just click and drag the map you see we've got the Explorer tool we're using right now but we don't always have that Explorer tool and so instead of having to switch to the explore tool and drag the map and then switch back to our existing tool what you want to do is just hold down C on your keyboard and you see that the little cursor change to a little hand and now I can click and drag and so I'll use this again later and show you why it's useful and so this is approximately where that map's gonna be so I want to click on the scanned in jpg and then here on imagery I've got this geo reference button and so I'm going to click that out I'm going to open up this geo reference tab and it's got all the stuff that I need to georeference the first thing I need to do is to bring that scanned in map into this area so that I can line these two up remember right now the scanned in map is just being plotted out in the ocean and so with this selected I'm going to come up here to fit to display and when I click this you see it brings that map and now it's in roughly the correct area and so now it's going to be much easier for me to line up this scanned in map so another thing that we can do to help us is we can make this map a little bit more transparent because we need to be able to see the points on the aerial photo that we want to match up to the map so with this map selected I want to come to appearance and here's the transparency slider and I'm just going to make that a little bit more transparent and you know 30 percent 50 percent whatever works for you there's 36 I'm gonna make it maybe 40 so now I can sort of see them both and so it's easier to find the places that I need to match up all right so now I need to go back to the geo reference tab and I'm going to need to add control points and control points are points that should match up on both maps and so when I select that here's the one trick you always click on the unreferenced map first so the map you're trying to fix you click on first then you click on the corresponding position in the aerial photo or the map that you're using to line things up and so I need to find some points that I can easily see on both maps what you need is something that's well-defined and easy to see and so crossroads are a really good starting point and you see we've got you know several roads on the scanned in map and we can see those roads on the aerial photo so let's find some crossroads that we can match up ok so I'm looking for some good crossroads to use as a starting point and so just kind of glancing around I'm looking for for characteristic things things that I can easily find in both and if you look here on the map you've got this kind of funny triangle-shaped road that connects to a bigger road and if you can look through the map to the aerial photo I can see that triangle shape there right so what I'm gonna do is I'm gonna look here you know where this straight part comes out and hits the main road I can see that right there so I need those two points to line up so what I'm going to do I've got the add control points tool selected I want to click on the map and then on the aerial photo but I need to be careful these need to be as precise and accurate as I can get them so I'm going to zoom in a little bit and here's where my keyboard trick comes in because I'd like to shift the map a little bit and I don't want to have to go all the way and find the other tool and then grab the map and pan it so I'm just going to hold down C on the keyboard and now I can kind of shift the map and now I can see the two the spots that I needed to line up a lot better so I'm going to click on the scanned end map first right at that intersection and that intersection is up here now I want to see exactly where it should go on the aerial photo and I can kind of see it but it's kind of covered up by this road that's on the map so what I'm going to do is I'm just going to turn that map off and now I can clearly see that intersection that in fact I'm going to zoom in on it a little bit more and I'm going to click on it and there's my first point and when I turn the stand-in map back on they're lined up very nicely and so that's a good starting point but you need to do several of these points to get this map shaped properly and lined up properly that's just a good starting point another trick is you want to spread them out and you want to kind of make them opposite of each other so I don't want to find another control point real close to my first one so I'm going to hold down C drag my map over I want to find a control point somewhere on you know the south east corner of the map and so I need to find another good Road intersection and let's just if we look on the the map here we can see a little road there but I don't quite see that on the aerial photo I can see this road here but I don't see a good crossroads to use until about right here so if you follow this road on the scanned in map you see it makes that little dip and then it hits a crossroad here and then if you look at the aerial photo you see it makes that little dip and there's a matching crossroad though that's that's a matching spot there so I'm going to zoom in and I'm going to click on the scanned in map first and then I'm going to come over here to the aerial photo and there they match up and if i zoom to I scanned in map you see it's starting to get closer to where it needs to be but I still need several more points spread all over the map so I'm gonna do that now until I'm happy with the location of this stand-in map [Music] okay I've got a few points every time I check a point they seem to be pretty closely lined up that's about as good as I think I'm gonna get it so you'll notice that I did a lot of crossroads but also if you look at somewhere like here I used like the corner of the dam and match that up anywhere that's a point that's easily seen in both the scanned in document and the aerial photo or underlying geo reference data that you're using and so now that I have my control points I need to save this otherwise all my work is missed now before I say that I can go to the control point table and you can see all my points and you can see the residuals which kind of give you an idea of how close the point is to where you want it to be understand that arcmap has to take the scanned in map and has to kind of stretch it and twist it to try to make it fit and so depending upon the size of the map and how well the it's scanned in and the quality of the map that was created it may or may not be easy to get all your control points fit exactly where you want them and so if they don't fit very well the residuals go up and you know it's not a very good fit but you can tell from this map that we've got a pretty good fit this table is also good if you make a mistake you can just come down here and select whichever one's a mistake and delete it and then redo it so now I need to save this and I could export it make a new one I had some trouble with that it seemed to take a long time the easiest thing to do is to just save the map now let's go look at the files real quick and so here is Windows File Explorer and here's the folder with all my files in it here's that sky rush scanned in JPEG that I've added and it's just that file and so if I don't save anything then next time I open up a project I have still just the same file and it's not geo-referenced so what I need to do is I need to save it and what it's going to do is going to add a couple of files that will help resize this JPEG and plot it in the proper location so I'm going to go ahead and hit save and there it went and if I come back to Windows File Explorer now you see we've got two new files with the same first name as our JPEG but with different last names and these files help to georeference this JPEG and so now if you want to move this JPEG and to a different folder or a different computer and you want it to still be geo-referenced you have to take all three of these alright and so that's it and so I can go ahead and close this and save my project and I have to update my arcmap but that's how I can take a scanned in map and geo-reference it

Channel: Timothy Spier

Views: 9,987

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Id: A5AeYtbt6sE

Length: 14min 14sec (854 seconds)

Published: Fri Mar 13 2020