 Hello, my name is Nico Tripsovich. I'm with the Archeological Research Facility at UC Berkeley. Welcome to the Practical Workshop Series. Today I'll be demonstrating how to geo-reference geophysical data into QGIS-3. In this case we have a slice map from ground penetrating radar and the slice map. It's 14 meters in one direction, so it doesn't match our site grid precisely. So I'll be showing you how to use the advanced digitizing toolbar in QGIS-3 to lay out exactly 14 meters in one direction. And then we'll geo-reference it and we'll clip the radar data to just the data areas that you can mosaic multiple radar slice maps together on a single layout. So let's go ahead and get started in QGIS-3. And I've got a site grid already created. And here's, this is what our GPR slice map looks like. You'll note that the north arrow is pointing to the left. So this is north. This east-west direction is 20 meters and the north-south direction is only 14 meters. So we'll geo-reference this into our project and the northeast corner of our slice map is going to fall right on the data in this demonstration. So let's go ahead and think about how we're going to geo-reference it. It's 14 meters north-south, so the 14 meter increment doesn't match our 10 meter grid here. So we're going to need to create two points on the south end to geo-reference to. There are two ways to do this. One is to simply, we're going to, we're going to put them, the geo-referencing points here in the points shape by all layer. And one way to create new points is to simply measure from the datum. And then using the ruler, watch the increments here just go 14 meters. It is very close to 14 meters. There it is. And then click and you get a dot. But that's going to disappear when you go and get the vertex tool to create a new feature. So you just put your finger on the screen and you can roughly, you know, zoom in. You're pretty precise and then go and get the tool here and click where your finger is. An accurate and elegant way to do this is to use the advanced digitizing tools. Now, we are in metric coordinate system, we're in UTM 10 North, 93 Epoch 2011. So I can use this advanced digitizing tool set. So I've got it enabled here and I've got snapping turned on, see the magnet. So the way you can do this is to use what's called, what's known as construction mode to create the offset. So we want to drop a point that's 14 meters south of the datum here. I'm going to go ahead and enter construction mode by clicking this you can also use the C key to toggle it on and off. And I'll click on the datum and I've got the snapping turned on so it's easy. And what construction mode does is it is it doesn't really create a point. It's a virtual it's kind of a virtual space for, for precise measurement that doesn't actually create vertices. I want to go 14 meters south. So to precisely guide that if I press the D key to the D there. And I've also got these guides turned on right here to these orthogonal angles 90, etc. So if I, if I just kind of drift south along this 180 degree axis and press the D key on my keyboard it highlights over there on the events digitizing pain and 14 return. And that's going to constrain my motion in a circle 14 meter circle, and I'll just go down south here and click. Well first I need to come out of construction mode so I'm going to press the C key. And if you look over in the advanced digitizing that toggles it on and off. Now it's off and I can click. And that's going to drop a vertex. And I'll name it southeast. I'll repeat the same thing here snapping is on. I don't want to leave a point here so I'll go into construction mode, and then I'll start moving south press the D key 14 return. Go down there turn off construction with the C key and then click. And this will be southwest. There we go. The next step is to use the geo reference or tool here in the roster menu. Open up our raster. It's called grid north. And once again we've got this is our data point and it's only 14 meters to this point. So the southern direction. So I'll go ahead. This tool is already selected. Go ahead and drop my first point here at the edge of my data. And now it wants the corner that wants the coordinates in UTM space easiest way to do that is choose it from the map canvas well first I'm going to make sure it's in the same reference system as the rest of the project. And then I'll click the map canvas and snapping is on so I just click there that populates. Okay. Next one is going to be this one I just created right on the edge of my data. Once again from map canvas and it's going to be this one. Okay. West in this case, the edge of my data from map canvas and it'll be this point. And finally this point goes here. The next thing to point out is that we have these four points in JPEG coordinate space indicated here, and the UTM coordinates are there. This is still all zeros because we haven't picked our transformation so I'm going to click the gear up here and choose your transformations. Just go with the defaults. And I'm going to call this mod. And save a geotiff. And we have compression options I'm going to skip that. I'll go ahead and save it. I'm going to run it with the arrow. Successful. You can see the ones I once I chose my transformation, we get the delta X and delta Y that is the adjustment between the two coordinate systems and then the residual provided here that are squared. I'm going to go with the georeferencer. I'm not going to save the ground control points, because this was a very simple. Your reference if I was doing something like a scanned map into a GIS I would probably save those because sometimes it's sort of an iterative process when you come back into georeferencer and make some adjustments, but in this case we're done. There it is. There it is positioned. Stop editing this one. What I'm going to demonstrate here is how to clip this gpr slice so that only the data area is showing. What this requires is that we have a polygon that limits the area of interest so I'll go ahead and start editing our polygon demo layer and snapping this turned on with the magnet so we can just go ahead and click the four corners, right click. Okay, stop editing goes there and let's let's put this underneath it so you can see it. And now we're going to use the raster extraction clip raster by mask layer. Oh, first I I'll select that polygon that I just created. Right here, selected. I need to highlight the layer. There we go. And then I'm going to use the raster extractions clip raster by mask layer input layer is our georeferenced gpr grid slice. And our mask layer is going to be this polys but just the selected features. Our coordinate reference system is the 93. And we're using the same one here. Let's go ahead and run it. The result is a clip layer that we can see here if we turn off the original layer behind it. This allows you to align multiple grid slices without that caller of the Jason information skewering the next two. Please note that this is a clipped temporary layer. And if you'd like to save this clip layer you should right click go to export save as and you can save it here as a geotip or any number of other formats. But it is just a temporary layer so it'll it'll remain in your project if you save your project but as long as you're on the same computer with those 10 files available, it'll likely reload. But you should make sure that your, your real data this original here with the caller and the polygon used to clip it are saved in a in a reliable place because this clip layer is just And that's all. Thank you.