Drones - The RIGHT way to Calculate Volumes with Agisoft Metashape

calculating volumes in agisoft meta shape or any photogrammetric package for that matter is a quick and easy process sometimes too easy perhaps so in this video I want to show you the process simple as it is but we're also going to go a little deeper to understand what it means to calculate volumes and some of the best practices that we should be employing if we are going out and measuring stockpiles so to begin we do as with any other project we perform the aerial triangulation clean up our tie points and we produce a dense Cloud we clean that up and we follow it up with the Dem digital elevation model I'm going to run through this very quickly and it's sped up of course but if you would like to know the processing steps that I use and why I use them please click the link that is up on the screen now so once we've got our dense Cloud obviously we want to clean it up and then the next step would be to produce the Dem it's from the Dem that we calculate our volumes in agisoft meta shape and these are the two volumes there's one here on the left hand side or on the west and another on the Eastern right hand side and we're going to start with the one on the right hand side today purely because it's on a flat surface and it's a simpler volume to calculate the one on the left as you can see here is battered against a berm or a shelf and for that reason we need to be very careful when calculating that volume that we don't overestimate or underestimate and that will be explained in the last part of this video so we now create our dim and we see it's a very high resolution of course flown with a drone usually our data will be of a very high resolution and creating the dim is a quick and easy process as well so before we get into the actual calculation it's always a very good idea to understand the type of terrain the stockpiles that we want to measure are sitting on to enable us and help us along in this process agisoft has a few nice tricks that we can employ on our data set so that we can visualize slightly differently to access this we go to tools and preferences click on the appearances Tab and go to Ortho View when we are there we'll see numerous options that we can change we can change the color gradient we can change whether we view the actual elevations or the slopes which is a very useful step and we also have the option to adjust the sun angle and the Azimuth of the Sun and this will adjust the shadowing that we see on any elevated element of our dim and it allows us to get a good understanding of the terrain is our stockpile sitting on a flat surface is it sloped is it like the second volume we're going to look at later on sloped and flat so play around with these tools just get a really good understanding of the region that you are working with you might find that you prefer to have these settings differently to the defaults for yourself in general practice so play around with them to understand what they do now viewing the Dem in slope mode we view our first stockpile and we see obviously that the stockpile is elevated and the sides are a little steeper on top it's quite flat and surrounding the stockpile it's generally flat but we also see there's an area we need to be careful of there are a few large rocks we might choose to avoid so take your time to analyze it very carefully because when we draw our shape we don't just want to be haphazard and sloppy about it we're going to be very careful we want to be precise so that we can calculate accurate volumes we then go to the polygon tool and we start to draw our shape around the stockpile so select the polygon tool and then with your mouse just click the left Mouse button when you want to create a vertex and here you can see I'm tracing around the stockpile trying to remain on the flat area at this point I need to try and skirt in between the two different dumps and I'm looking for a line that is as flat as possible in front one vertex to the next maintains the same elevation so we keep moving around our stockpile being careful to avoid any rocks need to decide do we go around or inside in this case I've decided to go inside of those large rocks so just keep clicking and when you're happy with your shape and you want to close it off you put your cursor over your starting point and you double click the mouse and that will close your shape the little flags that come up now are all of the vertices that we have placed and we can just review them for accuracy and decide if we are happy with the shape that we have drawn eggsoft has some nice tools to edit vertices if we want as you can see here the vertices are changing hover your mouse over the shape and press the letter i on your keyboard to add Vertex or the letter r on your keyboard to remove a vertex by doing so we can densify or simplify the shape so once we are happy and satisfied that this is a good shape we right click in it and select measure you'll see it will tell us the details of all of our vertices and we want to view the profile because we want to find that we have placed our shape on a surface that is as flat as possible in this case we see one Spike and one dip but the change in elevation from the minimum to the maximum is relatively small and in this case we can understand why we have these changes remember we needed to skirt between those two dumps and of course the terrain here isn't perfectly flat keep in mind as well when agisoft computes the volumes now we have the option to select a best fitting plane or a mean level elevation above which we will calculate our volume overall I'm satisfied with this shape when we select the volume tab we then see automatically it is on the best fit plane which tries to place a planar surface as best as it can by adjusting the angle tilt in rotation so that it meets as many of the vertices as possible we note as well that it will tell us the volume above the plane as well as the volume below the plane and the total volume if we look at the mean level we'll see that the difference is actually very small so it's less than a percent I would say in this instance which tells us that the shape we have placed is quite accurate and those small spikes we saw haven't played any role in influencing the volume so we can be quite satisfied with the result that we have seen here you can of course if you desire change and use a custom elevation level of course you'd only want to do that if you're processing using gcps else you are Reliance on the quality of the GPS data to ensure that you have absolute Z elevations but it's up to you and you will need to decide for your own project I have done another video where we compare the difference between volumes calculated when GPS gcps are used and also when they are not click the link above and you can have a look at that and see the results I want to show you quickly what happens if we have an erroneous point to show you the difference in our volume and why it's important to be careful if we ever look now at the final or the total volume we see quite a significant difference and a much larger difference as well between the best fit plane and the mean level also we see that the spikes we saw earlier are insignificant compared to the large Spike we see now so remember again just hover your mouse over that vertex hit the r key and it will remove it and then place your mouse at a better position hit the I key to insert a new vertex and here you can see we've returned very much to where we began with an accurate volume so that is how we compute simple volumes in eggiesoft meta shape without bases of course that's the whole other topic for another video let's move on to the more difficult volume now so if we have a look at the stockpile we'll see that a certain percentage of it on the southern end or the bottom end seems to have been placed or dumped against some form of slope or berm perhaps now what's going to happen is if we calculate a volume in the same way that we have calculated the simple volume the result that we achieve will be erroneous and that's because of the slope so it's difficult for us to estimate what is going on beneath the stockpile placed on that slope but a fair estimation would be that the slope is relatively consistent from this bottom section that we're viewing now in the Southwest and going up towards the north eastern part of it so the first thing I would like to do is to calculate the volume normally the same way we did for the simple volume we will then subdivide the stockpile into two parts extracting the slope area out and then doing the rest of the volume and we will see if there's any difference in the calculation and determine if it is important in fact to divide volumes up when we meet situations such as these so again like we did for the first volume we Trace around the outside trying to stay on a flat and level surface in this case as well we can tell by the color change in the Dem that where we are working now there's a slight drop that's occurring and so we already know we won't be on a perfectly flat surface so we do our best to stay at level elevations again we need to try and decide where we take our vertices to ensure that we are as level as can be and that is how we would have done this volume if it's were on a flat plane but let's measure it and see the results anyway and you'll note now when we view the profile how drastic these changes are and how very different it is from the first volume that we calculated we also see that rise in the dip towards the latter part of the shape where we anticipated we would have these issues and we can clearly see there's there's two very different elevations going on with the stockpile so what we're going to do is we're going to have a look at the the volume that has been calculated note as well the difference between the the best foot plane and the mean level and we're going to save this in Excel so that we can compare the two volumes later on once we have subdivided this volume in the suggested manner have a look at mean level and there we can see this discrepancy there there's a significant difference here typically in practice I know clients like to see percentages or differences below about three percent sometimes five percent if they're more lenient so the margin for Eric is quite small so what we're going to do now is to calculate the volume Again by subdividing the stockpile into two parts first we're going to place a shape that only includes the slope and to be fair we're going to use the exact same vertices as we used in the first instance and we will just sum the two parts together at the end so we perform the measure let's review the profile and there we can see this profile now it's far cleaner there's two very distinct areas that would be the upper and lower parts of that slope but they Plateau quite nicely so I'm generally satisfied with the result we have achieved over here so we want to take that volume noted down in Excel and then perform the calculation for the second part as well that's the first part done now we begin with the second again we click exactly on the originally placed vertices so that we are drawing a fair comparison here and we just Trace around the shape nice and carefully again and remember in metal shape when you want to close your polygon you just hover the mouse over your starting point and you double click it will automatically close the shape for you and bring up that dialog box right click on the shape we'll select the measure tool view the profile there again they're generally sloping shape which we saw originally because we know the bottom area of this profile isn't flat and then that second plateau you take the volume values and we place them into our Excel spreadsheet and now we want to compare the result so there we see we have a result that's close to five percent a five percent difference in the same stockpile from one method to the next as I said earlier on some clients are happy with five percent but those are few and far between and usually we would want to have any variance at three percent or below so this is just one example where you would need to be very careful about a complex volume subdivide it and then add the totals at the end that for the most part is a trip down the road on how we calculate volumes in eggysoft meta shape a quick and simple process the results are usually very good but it does require a careful and steady hand when placing those shapes as well as a good analysis of the terrain so that you do place those vertices on a flat area so that the volume you calculate at the end of the day is as accurate as it can be I hope this has been helpful if it has please would you like the video and subscribe thank you for watching

Channel: Geospatial Tips

Views: 21,209

Keywords: Drones, Volume Caculations, Metashape, Agisoft, Volumes, DJI, TerraScan, TerraModeler, Global Mapper, Photogrammetry, UAV, Survey, agisoft metashape, photogrammetry, agisoft photoscan, terrasolid, mine surveying, dji mavic, dji mavic mini, dji mavic mini 2, dji mavic mini 3, drone, agisoft metashape tutorial

Id: bfI8JAUKUpg

Length: 17min 42sec (1062 seconds)

Published: Fri Nov 11 2022