Hi everybody. I’m new here and I already have a question
I was asked by a local farmer to make a 3D model of his field. However, he is mainly interested in an accurate effective area measurement of his field, since it’s quite hilly. Of course, when you measure the area from above, in 2D, you get a smaller value than when you would measure the true area from a 3D model. If I make a scan and then select “2D -> Area”, which value will it give?
Hi everybody. I’m new here and I already have a question
To my knowledge: The 2D Area selection tool will not take into account the elevation change of a hilly area as it will base it self off of GPS coordinates of the polygon. This would most likely be best done by exporting a dense point cloud and moving into a 3D modeling or GIS or CAD software. You may be able to better extrapolate this information by using an app to count the rows of plants and use the spacing as an estimation. For a true Surface area though i would think you are looking at exporting into another application.
That’s a very fast and useful answer; thank you very much. I was afraid of that, but had to double check here, as I couldn’t find an answer anywhere on the dronedeploy website.
@jantheeven Thanks, i try to help out where i have knowledge as i have been in a lot of situations before. As a follow up here is an example of how Blender (blender.org), which is a free 3D suite can do what you need from a model utilizing its 3d printing toolset.
This should mean that if you have a preferred 3d software suite it most likely will have the same sort of functionality built into it somewhere. Hope this helps!
Awesome tip! I just downloaded it and apparently it supports .OBJ files, which can be exported by DroneDeploy. I’ll give this a go… Thanks again Scott!
Thanks, it does indeed support obj, and a myriad of other file types (stl etc) Let me know how it works out for you.
I sure will. Off topic question then regarding volume measurement. I just made a scan of my brother’s house and garden. Please take a look: http://drdp.ly/fh59KV
As you can see, most of the garden is below road level and he wants to level it. So, dirt needs to go in. I took off with my drone from the street in the bottom right hand corner, so I’m guessing this is zero altitude then? Or does it measure altitude from GPS? These are 2 very different things, but I saw both of them in the same article: http://support.dronedeploy.com/docs/elevation-toolbox
I have no clue if the fill value is correct, because I don’t know what the reference plane is…
Yes for the elevation map the map has a zero reference point from where the drone took off. It does capture the GPS data in the EXIF file attached to the picture, and this is used on DroneDeploys side for the photogrammetry. As to how the volume is calculated within drone deploy i would guess it is based of off the elevation map (as relative coordinate system should be fine to determine volumes, and without and RTK GPS or GCP; GPS altitude data can be way off).
I would love to see a visualization added to the model or elevation map for volume calculations to actually show you the reference plane…
these may help:
Thanks again mate; I did read all this stuff already, but it still doesn’t give me the reference plane for volume measurement. I just did an experiment and this proves that DD doesn’t use the take off position as a reference. For the elevation map, yes… for volumetrics, no. Take a look at the picture attached: the take off position is clearly higher than the base of the measured object (jungle gym). The fill is almost zero, which means it takes the surrounding light blue area as reference. If it had taken the take off location as a reference, it would have yielded a couple of cubic metres of fill, and less cut of course.
Nice i love experiments; so interesting the elevation map is utilizing the reference point, but yes there really doesn’t need to do that for the volume as this is done essentially by difference from my understanding. So you are using the best fit method which is going to generate a plane according the the best fit model, i am curious as to what the read outs are using the lowest point. Either case it still doesn’t really tell us how they calculate fill volumes ( as you would want the plane to be generated at the top and not the bottom), well in this case i find it is best to go to the source… gonna bump this to the folks at DD and see if we can get a more detailed explanation and maybe even a detailed tutorial.
Since the dense point cloud is georectified, it most likely utilizes this data for volume calculations; which still doesnt answer about where the fill is measuring to (highest point maybe?). Perhaps i shall have to run some experiments as well.
Good thing that you’re taking this issue up with DD. I did find a work-around for calculating the fill needed for leveling my brother’s garden to street level. I determine the difference between the highest and lowest point in the AOI (area of interest) by using the elevation map. Then I multiply that value by the area. This gives you the total volume of the AOI. Then I determine the cut volume of the AOI using “lowest point” instead of “best fit”. I subtract this value from the total volume and voila: you have your fill…
Thanks for sharing all the learnings and experiments - really great to see your usage of the volume tool and helps us understand where the confusing parts are.
For the area calculation you first asked about, @RemotelyPossible is absolutely correct - the area is simple the 2D area of the polygon - we don’t take elevation change into account at all. If you need to get the true area of a sloping surface, I’d suggest drawing a couple of lines along the slope sides which should show you the elevation profile (which @RemotelyPossible again nicely linked in his post a couple of days ago), which can help with the true area calculation. Depending on the complexity of the surface, the blender option might be simpler. One point of caution re the blender route: our 3d model .obj files are not georeferenced / scaled to real-world units, so you may not be able to get an accurate area measurement from them. If either of you have actually gone through the process it would be great to know if it does work out.
For the take off elevation question, again @RemotelyPossible is correct - we reference our elevation model to the flight take off altitude. The caveat is that gps altitude readings may be off by 5-10m, so we don’t always see the take off location sitting at exactly 0m elevation in the model. For really accurate elevations you have to either use GCPs or RTK gps.
For the volume measurement tool, we set the base plane for the calculation using the elevation of the points in the polygon you draw for the volume calculation itself. In your example above, we therefore used the elevation of the points you drew around the jungle gym to define the base plane. The volume cut and fill values will therefore change significantly depending on where you draw the polygon. Hopefully that makes sense…
Thanks again for all the detailed notes on your investigations and posting the links to our documentation - we love to see the product being used like this! Let us know if you still have questions or difficulties getting the information you need and we can find a way to help you out!
Hi Jeremy… thanks for the reply, but I already understood what you wrote above (the quote). The real issue at hand here is: we would like to see a visualisation of the reference plane when doing a cut or fill measurement. My example above, my brother’s garden, shows that it’s not easy to determine the fill of the big polygon (not the small one around the jungle gym; forget that one). He wants to raise the level of the whole garden to street level (in light orange/yellow), but there’s no way to determine that directly from the calculations by DD. You have to do it like I explained, with some added manual calculating. It would be fantastic if you could manually input the reference plane as an add-on to what already exists: the “best fit” and “lowest point”
Thanks for the kind words,
My follow up would be where does it make the top of that fill calculation is that to the highest elevation of the points you have selected? And would it be possible for the engineers to look into developing a tool that would essentially allow you to play with that in real time, setting it to where you wanted? (or should i get on writing an app do do this?)
Im going to test out the blender thing from a map ive done and let you know, the nice thing is even if the .obj does not contain real unit scale so long as i have a reference measurement from the dense point cloud i can force scale onto the model and should be able to get a fairly reliable measurement, ill let you know.
Ah, I see the issue, yeah we haven’t built the corresponding case of wanting to select the highest point of your volume polygon to be the base plane, or being able to specify a fixed elevation for the base plane. We definitely want to overhaul the visualisation and toolkit for the volume calcs, but I’m not certain when that will be… I actually think building an app for this would be a great idea! We have js apis that allow you to create volume and elevation annotations, so you should have enough there to do all the calculations @jantheeven has been doing manually.
Let us know if you get the blender approach working - would be really interesting to see if the scaling works out as you said.
Off topic here… but I’m getting no response on another thread: is the flight speed in simulation the same as the actual flight speed? And is the max speed the same as the cruising speed?
@jeremy Any updates on this? More specifically: has anybody looked into finding a way to visualise the reference plane for volumetrics? Or even better, the option to shift it manually? You know, like in Pix4D… Thanks!