I have a couple farms that I’m trying to do surface drainage on, but they are relatively flat fields. Talking maybe 10’ of elevation change in 300 acres. I’m just going to be mapping small sections at the moment (approx 40 acres).
Would it help the elevation data if I fly in a grid pattern or will it not make much difference other than really increase my upload/processing time.
What would happen if I needed to do a battery swap in a flight like this? Need to make sure I take off in exact same spot?
Any experience with this would be helpful.
Thanks.
Couple of things you need to know. By doing cross runs you will improve the accuracy but you don’t need to do a complete cross hatch. You can just do a cross hatch on the edges and middle which will save time and photos and achieve very close to the same accuracy as doing a complete cross hatch. BUT if you are using the resulting DEM for drainage I would definitely put down ground control marks or GCP’s to increase the accuracy and too make sure all your flights match together properly, as you definitely don’t want a step from one paddock to another. Hope this helps
Is there any easy way to place these GCPs. No offense but everyone makes it sound easy to include GCPs in their models when in reality it seems extremely difficult and expensive.
With that said, how much more is accuracy improved if all you are looking for is a rough DEM? From what I understand, GCPs mostly improve elevation accuracy and only slightly improve everything else including DEMs. (I could be totally wrong on that however).
I see the benefit to using GCPs but its also extremely expensive from what I know. Thanks for your help!
The main issue with not using GCPs is that you are then reliant on the GPS in the UAV, which means that the error in the position could be up to 10m/30feet out in vertical and up to 3-4m/ 12/16feet horizontally. So there are a couple of easy ways. One look up Propeller AeroPoints a few of the guys are purchasing these very easy to use basically throw them around the area and turn them on. BUT if you are flying the same area again and again it may be cheaper to have a chat to the local surveyor and put some permanent marks out and get him to give you positions on these. If you leave them out you would only need to get him there once. (IE Bash a 3foot steel pin in the ground so they will be there for years. The place a mark on top that can be seen in the photos) I have known some mines that use an old conveyor belt painted with a cross that they put down and then before each flight brush it off with a broom and repaint if required. Doesn’t really matter as long as they don’t move. Remember leveling will be the first step you can then get into NVDI and autosteering and spraying. Remember if you are getting a surveyor out put more in than needed as to get a few extra won’t be as expensive as getting him out twice.
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Thats great advice, thanks for the help. This may sound a little novice but I need to ask here with likeminded people rather than in the field with someone (A surveyor) who I am conducting business with. I was wondering what we should expect to ask/tell the surveyor and in turn, what we should expect to be asked/told by them when we request GCPs. I would rather be prepared for their questions than look novice and ill prepared when they start asking questions that I may or may not know the answer to.
Is it as simple as looking for the first survey company you can find and then telling them you need 5 GCPs? I feel like there is more to this process than that…
Yes a bit more complicated but not much. If you want you can send me a kml of the paddock and I can put in where I think you should have marks
- decide on the type of mark you want ie steel pin
- decide on the type of mark so you can see it in the photos ie paint cross or something more permenant make sure you can easily spot in photo. I often use 4ft painted cross although this does’nt always work well on dirt. I have used coreflute before but this disintegrates after a while in the weather
- place the marks approx 1000-1300ft apart or at the corner of your fields ie if you field is smaller just go for the corners if bigger you’ll need to split up with the distances no greater than the 1300ft. If your field is not square you may need extra at the bends. if you were to draw lines through you GCPs the entire field should be on the inside. if the entire 300 acres is in one paddock you may like to put one in the middle. If the 300 acres is divided in a couple of paddocks maybe put in the corners so you can fly and process separately.
- ask the surveyor to survey in the marks to GPS RTK accuracy 1-2inches in horizontal and vertical.
- I’d use your state grid ( not sure were you are )
- offer to show him were the marks are. this will save him time looking so he should just be able to drive up to the mark and take a shot.
- ask for the data in Hardcopy with datum used and points and softcopy as a CSV file. Just about everyone will take a csv file and you can read it in excel
- when you send the photos for processing send the csv as well for the GCPs and they will be able to process.