Hello
Our Organization would like to start allowing our new operators to perform GCP training. I don’t want to buy or rent a Trimble due to the cost associated. Has anyone used any mobile apps that provide similar GPS data? I realize that it will not be as accurate but that is not my concern now - I just want to practice the process.
Thanks!
I like the app: My GPS Location
If you average its readings over a 10 min period you should get bettery accuracy.
Regards,
Terry.
Thanks Terry!
Is this an Android or Iphone app? Or both?
Do you have an example of exporting the data to a format that is usable by DD GCP processing?
– John C.
John,
I use Android. There are 14 sharing options for the data. The data format I use is decimal degrees with 5 digits after the decimal or 1.1 meter accuracy. I have not yet used it to create DD compatible data but this should not be hard.
Regards,
Terry
If you’re not that concerned with accuracy why not just get elevations for the spots and then create the horizontal coordinates from the map. You can process the map without gcps then use that map to get the horizontal coordinates and put in your own elevations. You’ll be way closer than a meter.
You can also look into an option like the emlid reach RS+. $1,500 for a base and Rover.
Thanks for the input Michael - this is mostly a training operation. We want to to get our operators used to processing maps with GCPs.
How would you recommend getting elevations for the points?
– John C.
Just keep in mind that there are many ways to create GCPs so don’t think your going to be tied to $30k worth of gear. A benchmark and a $300 level setup works about as well. I would suggest you train on QGIS as well. It would be in your interests to learn as much about GPS, GIS and traditional Surveying as you can if you’re going to be serving clients.
John,
I took my cellphone outside and measured the altitude of a point over 5 a minute period using the My GPS Location app. The average of the readings were within +/- 5 feet of the actual elevation. This might be good enough for your training operation and could be zero cost.
Regards,
Terry.
@SolarBarn, have you been able to test your phone vs drone vs L1/L2 GPS? From my understanding, cell phones use assisted GPS (A-GPS) whereas their signals are assisted by triangulation from cell towers. This means that the coordinates will not be true WGS84 and will not match the drone even if it were more accurate. You can turn off your cell data temporarily though… I’m not saying that this isn’t a good option for them though.
Newer phones actually run dual-channel L1/L5.
I would recommend the Precision GPS app for Lat/Lon and GPS Averaging for elevation. The only reason GPS Averaging is good for both is it rounds the lat/lon to a tenth of a second, but Precision GPS doesn’t provide elevation unless you buy the Pro.
Sounds great!
Can you point me at this $300 hardware?
Probably not what you were thinking I was talking about… It is a traditional surveyors level. You don’t need a real benchmark if you aren’t trying to reference other data like an engineered plan, just something to nail the relative elevations of the GCPs. It is a two-man process or for a little more it can be one-man with a laser level. It’s a good practice that I would recommend anyone who is going to “survey” with a drone learn.
No cell reception at my site so it pure GPS from my phone. Again this offers him a no cost solution. But I like the ideal of using a laser level for spawning elevation values for locations away from a known reference. I do this around my site as a good way to check the elevation accuracy of my maps.
Regards,
Terry.
The other thing that has to be taken into account is whether a solution is providing ellipsoid or geoid elevations. Our use is based on certified local benchmarks and this will be a must if you are trying to be ground truth and relative to a survey or engineered plan. There can be several feet difference between these datums and ellipsoid shape doesn’t match geoid so you can get two completely different elevation differences on the same two points between the two models. This is why a certified local benchmark or at least setting something yourself (whether it is true or not) and collecting it via a localized GPS survey or running a level loop is so important.
I cannot stress enough how important this is if someone plans on providing drone services to construction companies. If you don’t, someone else will and they will never look back.
Unadjusted GPS provides ellipsoid elevation data. This can be converted to geoid for a given location. In theory the conversion could be done by simply weighing an object at MSL and then at the given location. For locations above MSL the weight will be less and the difference can be converted to an elevation increase above MSL. In practice expensive equipment would be needed to provide cm-level accuracy. So most use tables or models or hardware+software built into an advanced GPS receiver to convert an ellipsoid elevation to a geoid elevation. For a given location, and a significant distance around this location (hundreds of feet for sub-meter accuracy) the offset is fixed and can be looked up once and then reused. For John’s training exercise, it may be sufficient to just add the offset for his location to any ellipsoid-based GPS elevations he wants to use. Then the elevations will be reasonable compared to MSL-based topo maps and the like. Not cm-level accurate but ok for a training exercise. Who knows, maybe at his location the ellipsoid and geoid models are coincident and the correction is zero.
Regards,
Terry.
@john.culkin Good afternoon! I just wanted to check in and see if you ever had any lucking with your training endeavor? I think it is an interesting case that will surely come up again.