Georeferencing in Agisoft Metashape using GCPs

hello dr. Billy Joe here today we're going to learn a little bit about geo referencing using a D soft metal shape and data from a drone or UAV so we're going to go ahead and first look at our folder structure and make sure we're all kind of set to go in our field day in my class we did two different missions here's one mission where we recorded recreation field east I'm going to open that up and you should set yours up in the same way where you have a photos folder an output folder and an export folder and then also since you'll be geo referencing hopefully you already took your DCP points in the field using some sort of GPS high-precision GPS equipment or a total station or whatever it might have been and you also will have formatted it in the same way as I have it here you have the name your GCP you call it g CP two three nine whatever the numbers are your longitude your latitude and elevation you might have Latin long switch that's fine as long as we make sure we're switched in the program as well but you do want to set up set it up like this you can do it in text file and make sure it's tabbed a limp abdomen a door delimit in some sort of way I always just use tab delimited but add yourself will allow you to do many things so make sure you prepare it though like this we have your your columns named and then each of the GCP is nice and neat I will close that out we'll get back to that later go ahead and open up addy soft metal shape and load your photos in and run an alignment so what I'm bringing up here is a project that I've already completed you know from beginning to end but I went ahead and copied one of the chunks and brought it all the way back to just the alignment phase as you can see it here so that we can actually work through the geo referencing together so once you've run it on an alignment let's just show you here workflow alignment align photos you want to run it on high you can have your reference pre selection set up if you want to as well as your your generic pre selection checked off or uncheck them depending on what you want to do that's fine I usually have my key point limit at 40 thousand and then type point limit can be somewhere in the 4,000 to 10,000 range I typically will set it up just like this and hit okay we'll get our align photos and you should see that it it aligns pretty straight if you're using some sort of automated mission with its mission maker or you know pix 4d capture you should have some sort of automated flight path pre-planned and here we actually use the flight path we're going back and forth in one direction and then it turns this grid 90 degrees and then starts to go back and forth in another direction so this is good for actually creating maps you know ortho photos and also digital surface models in a systematic way so we we're assuming here in this tutorial that you've already run the alignment you everything checks out okay I want you to go over here to start us out and it is likely you'll have these already checked off now these are your photos this is all of your photos and this is the metadata on your photos showing lat/long and altitude per photo so if you were using a drone where the camera actually is being is stamping each and every one of your images and geo-tagging them with with your lat/long and altitude it's probably going to do something like this where everything's checked off all right we want to uncheck that because we're going to actually use a different set of coordinates to georeference this model because these don't quite have as much accuracy accuracy as we want so I'm going to highlight them all which you can easily do by clicking ctrl a and then one of those checkboxes and they're all unchecked okay so that's done now we're actually going to run a mesh at two hundred thousand Polly's just to get a solid surface here that we can plant these these points down as we mark them and you'll you'll see what I mean in just a moment when I what what we're doing there so I'm going to turn off our cameras just so we can see the baseball field and I'm gonna go to workflow I'm gonna go to mesh skipping dense cloud I'm gonna go to mesh and using the sparse cloud I'm going to make a custom mesh at two hundred thousand face count and hit okay it's gonna go fairly quickly because it's just it's just gonna make a surface out of what we have here in our sparse cloud now it's done look at it and as you can see it's it's not gonna look great it's not supposed to look great so we're not done we're actually gonna redo this match later on but we need to use this kind of surface to lay those points down on now I have a pretty flat field here but if you have any sort of topography you'll see some of the topography rippling through in the sparse cloud mesh so so that like I said this is a temporary measure just doing it so we have a solid place to put those points down on when we're when we're assigning coordinate so let's go ahead and begin the process of importing our GPS and click import that's this button right up here and we have to go back out to where that text file is click it and we'll hit open and it loads it all up right here now if you're having trouble seeing what's going on in terms of these GCPs listed here you can always resize this window to make it bigger or smaller so looks like we have our coordinate system plugged in which we used when collecting the points wgs84 tab delimiter if you use something else is your chance to either use semi colon comma space whatever it might have been I use tab and that's why it shows up this way exactly how I want it then we're going to go ahead and make sure it starts import row a to making sure it ignores this first one and goes right into GCP too all right and at this point you can go ahead and hit OK and it's going to pop up a little dialog saying can't find match for GCP to entry create new marker well we didn't create any markers here so obviously we want to say yes to all of these so we'll sit yes to all and it imports them and makes these little blue flags with the GCP number there and their correct coordinates where they're supposed to go now here comes the part where we actually have to find these GCPs in the photos themselves and lay down a point right where they're supposed to go so let's let's take a look here let's they just look through our imagery double-click a c1 here where they've already tried to plant a flag down on GC p7 I'm gonna zoom in and then you can see is that correct yes no where is it looks like it is kind of in the center there so I'm going to go ahead and just kind of move it to where I think that Center is for number seven and when you do click on it it turns green that means it's something that you yourself have actually confirmed so and you'll see that things actually will on-the-fly update themselves as you saw here there's some gray flags and these little icons some blue flags now so if I go to this one here double click that photo it looks like it the computer went in and put in a flag right on GC p7 and I want to shift it just a slight bit right there's a more IRS GCP 7 again okay so it looks like it's actually put in a few on GCP 7 now what I can do once you've put in about you know three or four is you can right-click on the GCP here filter photo by marker and over here in your photos pain the only photos that it should have are photos that actually have GCP 7 in them so I'm looking at 7 right now if I double click here it opens up another photo that has 7 they all have 7 in them and the best part of it is it puts the 7 right in center of your screen so you don't have to go searching for it and it looks like computer is actually doing a pretty good job making sure that that dots kind of in the center of our GCP now here's some that have grey if I want to I can go in and make sure that's you know where I where I want it right in the center and look it already updated a few more of these turning them blue all right so if I go over here and I head over to the right with this little scrolling thing you can see where it says projections it did 30 five of them just from the few that I I planted myself I think I maybe put three or four down and it's already got thirty five in the back for me so I I would just go ahead and start doing this with every single GCP until you get at least thirty per 30 projections down if you didn't get that many photos that where you couldn't actually put thirty projections on on each of these GCPs maybe ten would be a good threshold to go with so go ahead and I would say go ahead and start doing this for other GCPs that you might see let's take a look here now if you look at the model in the model view of shutting them shutting out one of these the photo itself click the flag and you'll actually see where the GCP is roughly are based on the coordinates that you put in there you have to actually hit this flag to toggle that on and off now if I go to GCP four and I want the photos from four but I haven't laid down any points a strategy you can use is making the camera show grabbing here the selection tool selecting the cameras that are overhead and then scrolling through make it list format scrolling through these we have to reset our filter because remember we had a filter for GCP seven and see if we can find that look there's some highlighted photos I'm going to go ahead and click on that and there we go here's a number four I'll plant one down there I know the next one the sequence was also yep and that one actually went automatically I didn't touched that one side with that so it looks like four has a few projections up nineteen of them so I should be able to right click and do filter by photo filter by marker and I've got a bunch of ones that should have a four in there yeah yep very good all right so what I forgot to do last time was hit this little button here which is to undo the filter so that I'm back to all the photos so let's do another one um take number two for instance we want to do GCP too when I close out the image GCP twos down over here so I want all the photos out of there so I'm going to highlight them a selection tool and then scroll through until I see them come up here up there's a bunch right there aha there's GCP - okay put that down and yeah it looks like it's actually doing it just fine looks like I have 14 projections just out of putting a couple there I'm getting GCP 3 I'm going to close that out there's GCP 3 towards the center selection tool just gonna lasso these guys in here and scroll through these four look like they have a 3 in there there's 3 and so the goal here is just to make sure that everything's in the center and that you actually are projecting at least you know ten to thirty of these flags and double check to make sure they actually go into the center so all right so go ahead and let you finish up that and and make sure that you actually do get through e to your GCPs that you're capable of doing something I do want to mention is that we took control points in the field and we know the distance between six and nine if you want to you can go ahead and use the six and nine that you that you collected in the field in terms of GPS points and geo reference using them but you can also leave them unreferenced if you want and use them as checkpoints but I often check using the little ruler here as well after everything is said and done the final steps geo referencing is to actually hit the Update button making sure every once in a while you hit update and it updates everything in terms of you know spatially where things are you get an update also on your error readout you know how much error you're actually introducing into this model based on the projections you've got there and then once you're completely done you want to run an optimized camera with the GCPs all marked into place and then you move on with the workflow where you build dense cloud and then you build a mesh and then you build a texture so the part of your referencing goes in after the initial alignment after creating a very temporary mesh out of 200 faces and then 200 thousand faces then you go in and you geo-reference in the photos making sure that you know all of these flags are planted in the center once that's done and you've been updating as you go at the end you hit optimized cameras right here and it reorients all of your your photos so that they're optimized for using the actual GCP is the actual GPS coordinates so that's pretty much it the rest of it you just take through the normal workflow and in meta shape you know making your you know dense cloud your mesh and then your texture and then the last component would be building a DM and building an ortho mosaic so you can see the normal workflows right in here then you build a DM and you build a north of mosaic and if you want to export those it's as simple as export export or that mosaic export the annual export as the TIFF file right in here so good luck

Channel: Alex Elvis Badillo

Views: 15,807

Rating: 4.9281435 out of 5

Keywords: georeferencing, agisift, metashape, GCP, UAV, drone, aerial mapping

Id: G09r5PXqhBc

Length: 14min 35sec (875 seconds)

Published: Fri Dec 20 2019