Cost effective ways to obtain GPS data for Ground Control Points

[adm_geomatics]

We work on multiple levels to coordinate (sometimes dictate). Being the end-user allows that. We duplicate a lot of work, because that is what government does. But at the end of each project I have at least two if not more sources to draw from to create our own internal as-builts at least as far as the civil package. We do this with the general contractor in parallel so that any gaps in either sets of our data is hopefully covered in the other's dataset. This has served us well with most projects that we have undertaken but there is always the outlier. Nothing is ever perfect 100% of the time.

Great workflow! This is very similar to how we do it when we are a Sub to a larger GC. Sometimes we provide all the Drone Services, sometimes with have to coordinate with another outfit like Multivista and other times we just do it for us if they have no interest. They usually come around about midway through the second wave of excavation and start asking for data, but the drone is not part of the construction contract so it becomes a Change Order.

Ironically on the subject of this topic the main problem we have had with coordinating with other DSP's is GCP's. Even though we have set them and are willing to share the coordinates.

 

[R Martin]

Great workflow! This is very similar to how we do it when we are a Sub to a larger GC. Sometimes we provide all the Drone Services, sometimes with have to coordinate with another outfit like Multivista and other times we just do it for us if they have no interest. They usually come around about midway through the second wave of excavation and start asking for data, but the drone is not part of the construction contract so it becomes a Change Order.

Ironically on the subject of this topic the main problem we have had with coordinating with other DSP's is GCP's. Even though we have set them and are willing to share the coordinates.

We inserted a section in the Title 1 documents that require 'x' number of surveyed benchmarks be set to USGS standards prior to the start of any earthwork. We define the coordinate system to be used (NAD83 2011 TX State Plane 4202 GeoID12B). We also require that the contractor submit all data in our preferred coordinate system.

 

[adm_geomatics]

We inserted a section in the Title 1 documents that require 'x' number of surveyed benchmarks be set to USGS standards prior to the start of any earthwork. We define the coordinate system to be used (NAD83 2011 TX State Plane 4202 GeoID12B). We also require that the contractor submit all data in our preferred coordinate system.

We as the contractor have a section in the contract that prior to the NTP there should be at least 2 vertical and 3 horizontal benchmarks encompassing the site. Usually we accomplish this by getting in contact with the Surveyor and/or Engineer at the time we receive the data, but it's in the contract just in case. This gets the discussion going quickly. Are you stating your requirements as the RPLS of record?

 

[R Martin]

We as the contractor have a section in the contract that prior to the NTP there should be at least 2 vertical and 3 horizontal benchmarks encompassing the site. Usually we accomplish this by getting in contact with the Surveyor and/or Engineer at the time we receive the data, but it's in the contract just in case. This gets the discussion going quickly. Are you stating your requirements as the RPLS of record?

No, not an RPLS. We are the curator(s) of GIS/CAD data for the university., We (as a department) just got fed up with the half-baked trash that contractors (and engineers) were charging us for so we worked with the other side of the house to establish what we decided was reasonable as far as deliverables was concerned.
We are spread out over four counties. Standardization makes it possible for one person to work the entire system without having multiple data files covering each unit in different coordinate systems and keeping all that straight. And if there is a genuine need to know, it makes it a lot easier to get the information you need. One-stop shop.

 

[adm_geomatics]

No, not an RPLS. We are the curator(s) of GIS/CAD data for the university., We (as a department) just got fed up with the half-baked trash that contractors (and engineers) were charging us for so we worked with the other side of the house to establish what we decided was reasonable as far as deliverables was concerned.
We are spread out over four counties. Standardization makes it possible for one person to work the entire system without having multiple data files covering each unit in different coordinate systems and keeping all that straight. And if there is a genuine need to know, it makes it a lot easier to get the information you need. One-stop shop.

That is a unique and interesting system you have going. No engineer or contractor that I know of would accept those mandates unless they were from the Surveyor of record and that's how it should be. No entity other than an RPLS should be able to dictate a coordinate system for use in land development. The good thing is that you are sticking with a standardized system based on updated datum from the NGS - I assume. Are you using Geoid 2012B or 2018?

I am guessing we may need to split this discussion?

 

[Stiets]

I use Aeropoints and they work really well as long as you set them where they get a good unobstructed "view". Like any other GPS instrument, they are subject to multipathing errors when in a built-up or obstructed environment. For $6250.00, they are an affordable solution when compared against even a mapping grade GPS unit that is robust and reliable (we own both). Also look at a Trimble Geo 7X with a mapping software package....I think they are running around $18,000.00 if I remember correctly but I do have CRS. I'm sure that there are cheaper solutions available; Garmin for example.
Keep in mind if you are doing your own GPS work that the hardware is only part of the package. You will also need the software to process the data you collect and Trimble Business Center (TBC) will run another $10,000.00 base without modules which you will need at least one....

All very great points. I would like to bring up that it is possible to post process GPS observations using NGS OPUS Solutions for free. Like everything else there is a learning curve and accuracy limitations but it is available. You would still need a survey grade GNSS unit but wouldn't need the 5k TBC cost. I prefer TBC because I post process network adjustments with GNSS, traverse, and digital level data.

 

[adm_geomatics]

All very great points. I would like to bring up that it is possible to post process GPS observations using NGS OPUS Solutions for free. Like everything else there is a learning curve and accuracy limitations but it is available. You would still need a survey grade GNSS unit but wouldn't need the 5k TBC cost. I prefer TBC because I post process network adjustments with GNSS, traverse, and digital level data.

OPUS is great when you have absolutely no information, but in most construction scenarios there is control already certified by the Engineer. OPUS is not efficient for drone use because it requires separate trips every time you have to modify ground control which is common inside the LOC of the site. Most of the time there are localizations involved so you have to go beyond the Engineer's control and collaborate with the localized coordiante systems.

 

[R Martin]

All very great points. I would like to bring up that it is possible to post process GPS observations using NGS OPUS Solutions for free. Like everything else there is a learning curve and accuracy limitations but it is available. You would still need a survey grade GNSS unit but wouldn't need the 5k TBC cost. I prefer TBC because I post process network adjustments with GNSS, traverse, and digital level data.

At some point we are going to be forced into TBC but that time has not yet come. We currently use PFO for all the processing.

 

[durapitch]

A GCP is just a base point that is used to tie in a given area to a known coordinate system. If I were you, I would check your county’s survey records (should be available online) and go hunt for a monument from a public land survey corner, 1/4 corner or 1/4 1/4 corner. Then you could just place a photogrammetric target atop the monument (line up center of target with center of monument) and incorporate this area into your mission when you fly so that you capture the target in your scan. This way you can tie your map or point cloud into a coordinate system of your choice from a well-established point of record.

You need at least 3 coordinated GCPS to mathematically solve the vertical plane (3D).

 

[adm_geomatics]

You need at least 3 coordinated GCPS to mathematically solve the vertical plane (3D).

...and most photogrammetry softwares require 4. Even on a 3-axis you get worse accuracy the closer to or beyond the single point that is the furthest from the other two. We require 4 on our localized GNSS networks.