Concrete Inspection Advice

I have an inspection job coming up and I had a few questions I was hoping to get some advice on. The job will be to fly 42 acres of concrete panels at the airport and to export an aerial image into CAD where the airport’s gird system can be overlayed to perform an analysis on the condition of the concrete panel by panel.

1.) I’ve read on the forum that people are having trouble unlocking missions in NO FLY ZONES even with DJI GEO authorization. Is this going to be fixed relatively soon? If not, does anyone have any experience with Skycatch?

2.) Can DronDeploy deliver the resolution needed to see cracks and spalling? Will a Phantom 4 be enough to deliver the required resolution?

3.) Does anyone have any experience with a similar mission? If so, are there any specific camera settings I should keep in mind? Does a specific time of day (lighting) help? What altitude and DroneDeploy Advance Planning settings should I employ? I’ve taken some test static shots and I can clearly see the cracks at 100ft. Will this translate to moving shots?

4.) Lastly, do you think I can accomplish this with a “PRO” membership or do I need to have a “Business” membership? I figured I would break the 42 acres into 2 or 3 maps to get around the 1000 image limit.

Thanks in advance everyone. I’ve gone out and completed 2 maps already; one at home and one at a concrete parking lot. I didn’t get the resolution I needed, hence all the questions.



1.) I have not seen where this has been resolved. I was readings the same threads as you. I would reach out to the DD staff directly, if I was in your position.

2.) I think if you fly low enough and with enough overlap you may be able to identify the cracking at the airport. Are they looking for cracks over a certain gap?

3.)I would try to do at a time that would reduce any possible shadows. The good thing about airports is that there are fewer things to cast a shadow. I would recommend 11am-2pm. In addition I would fly at a lower elevation, which still allows you a good stitch. Always better to be more detailed, especially if you are getting paid :slight_smile:

4.) I hate breaking up missions and just submitted one with around 3000 pictures so I am the wrong guy to ask :slight_smile:

Good Luck!

Hi tverhoeks,

I have a very similar project to you. I have airside areas to map and model (inc. buildings). I reached out to the DD support in advance which was very useful. My reply is based on this, and my experience from other missions so I hope it can be of use.

  1. I have not had this problem (yet!). I have had other issues in the past (now resolved) around the DJI settings not carrying over to DD. E.g. geofencing set in DJI Go, but DD thinking that I was going beyond the limits. My advice here would be to trial as much as you can before you get to the job. i.e. set up some kind of dummy run (with permission!) if possible. Depending on where you are in the world, permission from air traffic is pretty fundamental (obviously!). I have created some additional ops procedures to satisfy the airport requirements, but this will vary depending on where it is.

  2. Probably! This depends on your expectations and the size of the crack :slight_smile: I have the X5 on an Inspire Pro, which is 16MP. I think you will be at 20MP(?). I have been able to see decent levels of detail down to consistently 1.6cm/pixel, this requires oblique images as well as ortho.

  3. You need to strike a balance here, if you are too low you may get stitching issues. Also I have found that if you set a relatively high overlap at low altitudes the aircraft travels VERY slowly. We came to the conclusion that c. 200ft (set to 60m in DD app), and 80% front, 80% side laps were practical for both speed and detail. Throw in some obliques at 45 degrees and you will likely improve the res. Generally there is a lot of variation in concrete so it stitches pretty well. Camera settings have always been on auto. I had a focus issue at one point so it is best to check your pics (can use DJI GO) after each mission to save you having to go back to re-capture. I have found that a sunny day but slightly oblique sun angle helps (as long as there are no buildings/trees shading the survey area) to pick up some of the finer detail in flat, hard surfaces. Also, you can get significant reflection if the concrete is quite white. Moving shots I have not found to have an adverse effect on the detail (shutter will be pretty fast if sunny).

  4. I have Business. For larger areas I have split them up in any case. At the overlaps I mention above you will get a lot of data. The uploader will tell you that resolution may suffer if you go over 5GB at one time. My experience leans me toward creating some smaller maps and then getting DD to stitch them all together afterwards. You will need GCP’s for this, but if you are tying into a grid you will need this anyway.

As an aside, depending on how you format your sd cards, DJI will group the images into folders and name them from 1 to 999, then create another folder and start again. Obviously you can drag them into a new folder and the uploader will work out where they are, but it is just annoying and makes your data hard to manage. I am going to try formatting in exFAT to see if this means more than 999 images per folder.

Happy mapping.


Hey guys,

Thanks for the advice. It is much appreciated. Negotiations are moving forward with the consultant and airport whom I’d do the job for so it is looking promising!

Couple of follow-up questions.

1.) Do you think camera/lens filters are advantageous?

2.) @Peregrine, could you explain the Oblique images you mention further? Do you take those within DroneDeploy or just some static shots in DJI GO to add more detail?

3.) What have you done in regards to Drone Insurance? Verifly’s policy by flight approach seems like a great system for someone who does not have consistent flights to justify an annual insurance policy, but sadly it seems they won’t give out policies for the restricted airspace. Does anyone have experience with contacting Verifly with the appropriate authorizations and setting up a policy?


I haven’t used filters, I guess this is potentially useful if it is particularly bright and you have a reflective surface. I am not sure how the auto settings will deal with this on the camera, i.e. which of shutter or aperture will be adjusted given your filter. A fast shutter speed is probably not a bad thing when you are moving in any case. I would be interested to know how you get on with this if you try it.

Re the obliques, I have found you will need to experiment with this. More is not always better. There is a very good support article here: Definitely avoid sky in the image.

I am in the UK, so insurance may be difficult. I have an annual policy, but I did increase my cover to GBP10m specifically for this job and jobs like it. I have confirmation that it covers restricted areas and air side works, but it wasn’t cheap!


Hey @tverhoeks

If it is a terribly bright area you might want to through on an ND filter, but if you do you’ll want it on the entire time. it is possible that this could have a negative effect on mapping, so test it out first. As to the settings since the light is filtered prior to hitting the cameras sensor the camera will adjust the settings appropriately. ND Filters may cause an issue as they tend to blur motion slightly. Since it is a still picture as long as the shutter speed stays reasonably quick you wont notice it but if it starts to go over 1/60 th of a second i would worry this will effect the overall quality of the map.


Scott Lashmit