Georeferencing Imagery in ArcGIS 10.1

hello this is Rick Marshall from vertical Geo welcome to our geo referencing in arcmap 10 tutorial this is not a tutorial on how to produce an ortho rectified image but rather a tutorial on how to simply georeference a raster file to an existing image or map that is already geo-referenced many times we work with scanned maps or images that don't contain a spatial reference system this happens very frequently when you are working with historic maps or images when we look at an old aerial photograph the different parts of the aerial photograph look accurate in relation to the other parts of the same photo but they are not tied locationally to any specific point on the ground to make these images and maps useful in a geographic information system we need to define the images and maps locations using map coordinates and assign a coordinate system to them then the images and maps can be accurately tied to points on the ground and import it into a GIS as a mapping layer they can then be viewed queried and analyzed along with other geographic data we have done this many times for our local customers who need to use aerial photography from the 1940s to the 1970s and have it work seamlessly with images that are current to add capability when planning projects and this tutorial we'll be working with arcgis desktop 10.1 so let's go ahead and get started first you need to have your source maps or your images to be geo-referenced already scanned and saved in a GIS readable format a tiff or jpg PNG or gif all work well but a PDF will not work the next step we need to open a blank map in arcmap I already have it opened on our ArcGIS desktop application here for the video so let's add the target imagery to the map so in order to do that we're going to come over here and left-click on the plus sign which is the add data icon and we're going to add a fallon downtown imagery from 2012 vertical geo took this photography and processed it for the city of O'Fallon in 2012 when you open up a new instance of arcmap and you add an image to it that is already geo-referenced it defines the geo reference of the coordinate system for the project so we can come over here to the left and right click on the layers icon and go all the way down to the properties link and that will open up our data frame properties dialog box and in that data frame properties dialog box is a coordinate system tab and we can see the highlighted coordinate system for this image is the nad 1983 state plane Illinois West feet coordinate system if we wanted this is the coordinate system assigned to this image but we can change the coordinate system for the entire layer if we want by just scrolling up through and finding the coordinate system you want to use in this case we use the state plane but you can also use a world or a world sphere vase coordinate system as a projected coordinate system there are geographic coordinate systems you could use also in this case though we're going to use the state plane Illinois West it's the native coordinate system for this imagery and we're just going to go ahead and use that for this project so I'm going to click on OK and that just tells me that we're going to use that coordinate system now we're going to add the unreferenced source image to the project and this is the image that does not have the geo referencing in it for this project today we're going to add a fallon park image that was taken at the same time so when we go to add the image the first thing that pops up is a dialog box that says create pyramids for O'Fallon park this raster data does not have pyramids or contains insufficient pyramids would you like to create pyramids pyramids help the image load faster on the desktop software and on web-based viewers and eventually we will create pyramids for this image but for this exercise we're going to be working with the image and we're not going to create pyramids until we're done with it so I'm going to click on no and then we get a second dialog box that says the following data sources you added or missing spatial reference information and that is true because we're going to be adding that the spatial reference to this image so the O'Fallon Park image does not contain a coordinate system right now and that's the subject of this video is to define that coordinate system for the O'Fallon park image so this is fine we're going to click on OK and that will import the image along with the downtown image but you don't see the image on the extent in the desktop software that's because when an image does not have a geo referencing system the software automatically places the image at zero degrees latitude and zero degrees longitude and it draws it there and to see the image we can right click on the O'Fallon Park image and go to down to zoom to layer and it shows us what the image looks like but it does the image doesn't know where it's located so it's at zero degrees latitude and zero degrees longitude to get back to the downtown O'Fallon image we can right-click on that and go back to zoom to layer Oh fallon park is in the bottom right hand quadrant of this image and what we're going to do then is take the O'Fallon park image that has no coordinate system reference to it and we're going to reference it to this image of downtown O'Fallon and add the the coordinate system for this image to the O'Fallon park image so there's a couple different ways that we can do that first off we're going to be working with this O'Fallon park area so i'm going to zoom in to about the same extent that we're going to be working with today so I'm just using the ESRI zoom tool the ArcGIS zoom tool and so we zoomed in on the downtown O'Fallon image to the area that includes O'Fallon Park um if I'm on my copy of ArcGIS desktop the geo referencing toolbar is already in place and we'll be using this toolbar today if it's not on your copy of ArcGIS you can either come over here to customize and click on it and go to toolbars and add in the geo referencing toolbar you can turn your toolbars on and off using that command or you can come to a blank spot here in your toolbar area and right-click on it and the same thing you can add your geo referencing toolbar right there it will typically show up down here in the map window and I just moved it up here and docked it okay so here's what we want to do you want to take the O'Fallon Park image and georeference it so I go ahead and I click on left click on O'Fallon Park to select it in the table of contents I come over to my geo referencing toolbar and in the choose geo referencing layer drop-down list I make sure that O'Fallon Park is the one that I have selected okay what ESRI does for us in arcgis is they make it a little bit easier instead of having to go back to the O'Fallon Park image all the way down at 0 degrees latitude and 0 degrees longitude and try and move the whole thing up here we can take the area that we have selected right now on our desktop mapping tool and we can superimpose that O'Fallon Park image on top of this and we can do that by clicking on the geo referencing drop down list and clicking on fit to display and that will move that image that was down at 0 degrees longitude zero degrees latitude and move it up here into our workspace and you can see it's very confusing right now to be able to look at which images which so we will be using the selection tools to the left of in the left hand portion of the table of contents to turn on and off the different images as we as we use them okay the way that we make the points on the O'Fallon Park image geo-referenced to the points in the O'Fallon downtown image is via control points the downtown O'Fallon image is the target image the O'Fallon Park image is the source image so here's how we do this in your geo referencing toolbar if you move over to the right just to the right of the choose geo referencing layer drop-down list you have your ad control points tool these points will enable us to link parts of this image to the other image so it'll will find a distinct point on the O'Fallon Park image and click on it and then go find the same point on the downtown O'Fallon image and click on it and it tells the O'Fallon Park image you need to move to this point to make your image accurate so here's what we're going to do we click on the ad control points tool and we go over to a distinct point on the O'Fallon Park image and I'm going to zoom in to a distinct point which is this corner of this is the KD cave-ins community center and I am going to I know I can find this corner of the building on both images so I'm going to click on it here on the O'Fallon Park image and then click on the foul on downtown image and click off the O'Fallon Park image and now I'm looking at the downtown O'Fallon image and this again is the KD Cave and center and this is the same spot so I'm going to click here and what this does is tell the O'Fallon Park image this corner of KD caimans is not located where I think it is it's located here and it will move the image so that those points overlap so let me turn back on the O'Fallon park image and you can see those points overlap now I'm going to zoom back out to the entire layer but you can tell down here at the borders on the bottom of the image and around the outsides that it doesn't line up very well so the entire image hasn't moved the only thing that's moved is the portion of the image that is associated with that Katy cave-ins Center so we're going to take a few more round control points here you want to use always a minimum of four you can use as many as you want to make the image look good but just because you use more control points doesn't mean that your image is going to be that much more accurate so we're going to go use some control points in the middle of the image and several around the outside we'll do that over the next couple of minutes here so I am going to zoom into the ballpark and I know there's some unique features down there that we can use to as control points I'm going to use the center of home plate and look there we can still find the center of home plate on the downtown O'Fallon image also and that'll snap the center of home plate on the O'Fallon Park image to the center of home plate on the a Fallon downtown image and after we do this a few times with a few different control points you're going to see that the image will start to overlay exactly on top of one another I'm going to do one more here in the center of the image I'm going to use one of the tennis courts here to as a control point a nice definable place here probably about right here where the two lines intersect you can also use the base of these telephone poles or light poles anywhere that you know that you can find distinctly on both photos will work now you can see our control point 3 is not very far off it's pretty close zoom back out to the extent of the O'Fallon Park photo so I think the center of our photo is doing ok we're going to go do some control points around each of the corners all right I am going to use the corner of the emergency services department here as another control point and you can see they're getting closer and closer we'll do one up here in each of the corners use the corner this chimney I know I can find this event on top of this house in both photos sorry and I'm going to use the bottom of this light post at the BP station okay so I've got control points spaced out in all the corners I've got a few in the center of the park and that's all we're going to use for today if I had more time I'd go back and probably add another ten control points or so but this is how you use control points to tie the two photos together so if you have um any doubt on some of the control points that you used there's ways to go back and check that out on the geo referencing toolbar on the right hand side is a view link table if you click on that this will give you a list of the control points that you used so it's got all seven of them listed here one of the more important items here is this residual column and this tells you how much error there could be in that control point based on how it relates to all the other control points it's heavy into mathematics to come up with the residual values what you're looking for is something consistent and they're all semi close to each other if there was anything to the left of the decimal point anything more than about a one point zero I think I would go back and remove those control points and you can remove them by you can click on them too so that it will not use that control point or click on it again and it will down here on the bottom there's a transformation drop-down list that lists several different transformation mathematical formulas you can use for this geo referencing the one I almost always use is a first-order polynomial and that's what I'm going to use today each of them will warp your image a little bit differently to make it fit on top of the target image so I'm going to keep all those control points they all look good today so if you're satisfied with the geo referencing and that in this example today I am then we're going to go ahead and update the image to include this geo referencing to include all the control points and there's a couple of different ways you can do that if you go up to the geo referencing drop down list you can click on update geo referencing and that just saves this picture in the current format and so I'm going to go ahead and do that and when you do that it takes the image which was in a temporary status and now makes it permanently in this space and it takes away you can't see the control points any longer turn on the other image and you can see how you know the roads all connect together and in the parts of the image all overlay on top of each other very nicely the other thing that you can do is you can instead of update geo referencing you can click on rectify and what that does is it creates a new image and saves it somewhere else for you to use at another time either way is fine they both work so right now you have we've gone ahead and we've geo-referenced the O'Fallon Park image to the downtown O'Fallon image that's how you add a coordinate system to an image that doesn't have one so if you have a historical photo from the 1940s of downtown O'Fallon and you want to show it in your viewer or on your desktop to see the amount of change that's happened between 1940 and 2012 you can scan it in bring it in as a JPEG and do the same process you find distinct features that you can find in 1940 and compare them with the same distinct features in 2012 you can use your control points to georeference the photo and in the end you'll have two different products from two different time frames you can use to analyze change over time and increase your sexual situational awareness of what's going on on the ground there well I'm Rick Marshall and again thank you very much for tuning into vertical geo our YouTube channel this has been our tutorial on geo referencing in arcmap 10 if you have any questions please feel free to comment below thank you very much

Channel: Rick Marshall

Views: 109,603

Rating: 4.8233767 out of 5

Keywords: ESRI, ArcMap, georeferencing, imagery, remoe sensing, VerticalGeo, ArcGIS, Georeference

Id: cAPykiB2YyA

Length: 21min 20sec (1280 seconds)

Published: Fri Mar 21 2014