Inspire v Phantom for mapping

[George Templeman]

For site surveys you need GCP's to cm level accuracy. That means either buying in RTK GPS or hiring it per job. The Inspire's GPS is only consumer grade, no use for surveys I'm afraid. You then have to process the data with either dedicated software like Agisofts Photoscan Pro at $3000 or the likes of a Pix4D subscription. Even for the aircraft alone plus batteries and extra chargers I think your budget is way too low.


UK PFAW holder
BNUC-S qualified

Hi there, interesting conversation. We use 3D laser scanning to produce pointclouds of buildings which can use just as clouds in Autodesk Revit for visualisation of the existing site incorporatng a new proposal. As the laser scanner is ground based, we also sometimes map the site with our inspire 1 to produce and aeial based cloud. We can now merge the 2 clouds using the latest version of Autodesk Recap in to a single cloud to produce a complete cloud. We do not use GCP's in this process. I also use Recap360 Pro to process the data to produce the cloud. £40/Month. These scans are not geolocated with survey grade GCP's as for visualisation it not that important.

If the project proceeds, we can otain a full GPS based topographical survey, that would give us some accurate GPS cords of known points, that could then be used to reprocess the photo data from the inspire to give the better accuracy. To be honest, even when we have the GPS topo we have never reprocessed the data, as at that point we have a CAD file of the survey data, that can be used for the detailed design of the project.

What I am trying to understand is, do GPC's actually improve the accuracy of the point cloud, so when it is processed, it is more accurate, to take measurements from, or does it just accurately geo-locate the point cloud. The same for ortho site photo output.

At the moment, for our workflow, pointclouds are great for visualisation, but our need for accuracy comes when we have to produce construction drawings. Here a CAD file, GPS based Topo survey gives us the data required and it a lot cheaper to hire in this complete service, than geolocate when flying with an Inspire one, process the data and produce a CAD file buy modeling over the ortho photo. Pix4D has tools for this, but it still seems long winded.

 

[IrishSights]

For point clouds of buildings I always have linear scale bars placed around the building/object. I use the 0.5m GCP markers as scale bars for larger targets. I then integrate those into Photoscan Pro. That gives me real accurate measurement ability where geolocation is not needed. I use Autopilot Pilot's Orbit, Focus or Waypoints to get the imagery.

PFAW Holder
BNUC-S Qualified

 

[George Templeman]

Useful tip, thank you.

I too use Autopilot, amazing piece of software. Use Mappilot for ortho mapping.

What about the GCP's and accuracy or geolocation, any feedback on that, would be appreciated.

Thanks

George

 

[bluelight.support]

I use Autopilot Pilot's Orbit, Focus or Waypoints to get the imagery.

Using that is it possible to get the app to take images every x seconds ? Ive never used that, I use the Pix4D App on android and fly manually and it takes images every x / y m

 

[IrishSights]

Using that is it possible to get the app to take images every x seconds ? Ive never used that, I use the Pix4D App on android and fly manually and it takes images every x / y m

Yes you can set it from 2sec upwards. Even though it's flying a predetermined path you can still alter altitude and gimbal pitch during the flight. For buildings I usually do 2 orbits. One fairly low and the other higher and a little closer. The odd time I use ground images too.

PFAW Holder
BNUC-S Qualified

 

[bluelight.support]

What about the GCP's and accuracy or geolocation, any feedback on that, would be appreciated.

I would say they are vital. Unless you are able to produce rtk data and process that straight into your data.

My workflow is normally

1 take geo located images via inspire 1 pro
2 readjust the - sea level to + sea level in exif data
3 take into Photoscan Pro
4 align images
5 add gps control points
6 build point cloud
7 build dense cloud
8 build mesh

obvisouly tweaking the options to your fav. settings.

In the meantime, I would go round the site using common sense to take reference ground control points, using fixed furniture and features. Using something like the Geo 6000 with CM accuracy and Terracync and external antenna at 2m, locate your point - add feature, collect data for a good minute or so per point to get a good 60-100 data points (remember the 600 is 1hz) - I also take an image of the point as well which is geo referenced. Its important to note i am not using a realtime RTK data feed here, just the kit which can use rtk real time. In normal mode, this will get anything from 20-60cm accuracy.

I then get the data back to the office, and post process it with Rinex data for the time period and Pathfinder office to create my CSV import file. This will then give accuracy of normally 1-3cm. It is this data I then use in processing.

I cannot see how you can advise accurate analysis for anything geospatial without this process.

I went for post processing as it saved me the £2k per year for data feed but if you don't have financial restraints and good mobile service, then you can get 1-3cm accuracy in the field using realtime.

Hope that helps!

 

[bluelight.support]

Yes you can set it from 2sec upwards. Even though it's flying a predetermined path you can still alter altitude and gimbal pitch during the flight. For buildings I usually do 2 orbits. One fairly low and the other higher and a little closer. The odd time I use ground images too.

excellent - time to have a play!

Are you using X3 or X5 and if X5 what lens ?

 

[George Templeman]

I use Autopilot for Waypoint missions for video. I use POI for 3D pointclouds. When using POI, I take manual photos. I am not sure, but I think there is a restriction in the DJI SDK, that limits the no of photos per second. So I set a slow speed for the POI and take lots of photos, more the better. If a complicated building, it helps to manually fly as well to get more photos around the permitter of the building at different height. As I say the more photos the better at the highest resolution you can. There is a marked difference between the P4 and the Inspire 1 Pro. Autodesk Recap360 Pro processes the image in the cloud.

For mapping I use Map Pilot waypoint mission to capture the Nadir images and again process in Recap360. If as some others say, this form of mapping is not reliable enough without RTK GCP's, then a ground based Topographical survey with a total station / RTK rover is the best bet, which in my field seems to make an aerial ortho image a very expensive option as you are doubling up on the work, i.e. Aerial Mapping and a GPS / RTK based topographical survey, when the latter can give you a Geo-located CAD for use in our architectural work. May be different on very large site, when aerial mapping can cover a lot more ground quickly than a Total Stanton based survey.

 

[bluelight.support]

There is a marked difference between the P4 and the Inspire 1 Pro

What lens are you using?

 

[bluelight.support]

then a ground based Topographical survey with a total station / RTK rover is the best bet

The arial data is good but you just need the GCP to align the data and make it geo accurate. The Inspire 1 Pro does a good job and the GCP just tie it all together. I use 5-10 points which is a 20 minute job, not a complete total station and rover survey (apart from anything I'm not qualified for that)

 

[George Templeman]

Standard 15mm shipped with the X5. I am not a photographer, by any means. 16mp just produces better pointclouds than a 12mp camera

I'm just trying to find out I'd aerial mapping is worth the effort if you have to go to the trouble of hiring a RTK GPS rover system to make the output accurate. If I have to hire a survey team, they can provide the CAD data I need without the aerial photo to look at. ( although probably not on a site of 10 acres or more)

 

[George Templeman]

The arial data is good but you just need the GCP to align the data and make it geo accurate. The Inspire 1 Pro does a good job and the GCP just tie it all together. I use 5-10 points which is a 20 minute job, not a complete total station and rover survey (apart from anything I'm not qualified for that)

So if I don't need to geolocated it to 1-3cm, the data is still accurate to use to measure distance to boundaries, building lengths etc.

 

[bluelight.support]

So if I don't need to geolocated it to 1-3cm, the data is still accurate to use to measure distance to boundaries, building lengths etc.

What accuracy are you trying to achieve or will you be happy with ?

 

[George Templeman]

Good question. My gut says I want it spot in! but in reality Measuring from a build to a boundary, probably 2-3cm on buildings lengths 1-2cm.

For some buildings we can laser survey, that gives us the accuracy we need, but some sites we only have a time / cost window that makes an aerial survey viable, i.e. half day on site, back to the office to cloud process overnight.

 

[George Templeman]

Spelling!!! I meant spot on....

 

[bluelight.support]

The issue i have is the GPS accuracy of the Inspire 1 Pro shows as 5m under photoscan pro and the mean error levels looks to be around 10-50cm on the x and y and 40-120cm on the z axis. Therefore there is still an potential error of 1m between points which is mitigated using the GCP to tie all the data together.

My thought would be no i wouldn't be happy with that. However others on here might know better / more qualified than me.

 

[George Templeman]

Thanks, getting the jist now.....need to delve in to Recap360 settings to understand how to manipulate GCP data in the processing.

 

[bluelight.support]

need to delve in to Recap360

are you using Recap360 or Recap360Pro as there is a massive difference between their capability etc

 

[IrishSights]

I use Autopilot for Waypoint missions for video. I use POI for 3D pointclouds. When using POI, I take manual photos. I am not sure, but I think there is a restriction in the DJI SDK, that limits the no of photos per second...

Auto Pilot uses its own Flight Controller (as well as aspects of the DJI SDK) so it's from 2 sec up. Any of the the flight modes can uses this including POI/Focus modes.

PFAW Holder
BNUC-S Qualified

 

[George Templeman]

are you using Recap360 or Recap360Pro as there is a massive difference between their capability etc

Pro version