Activity Feed › Discussion Forums › Strictly Surveying › Topcon FC-250 APC correction?
Topcon FC-250 APC correction?
Posted by OMEGA-ThundeR on June 15, 2020 at 6:25 amHi,
I’m new in the surveying area and been working in the business for about 6 months now. Recently i found my first error in measurement with an offset of 10cm in Z-value.
I was working with a Total Station and used reference points (reflectors) that were given to me. So far so good, there was however a height point to check and i was 10cm to high. It might have been the correction i needed for my pole (2m length to ARP) and the mirror i used (ads 8cm from ARP).
I just corrected the height in my fieldbook so atleast the height profile was right.I didn’t have time to check with my GPS, but it made me think….
I allways set my pole length in my fieldbook to 2m and don’t add the correction to the GPS’s APC (~100mm) or the mirror center (80mm). Never had any issue’s with that and height points not made by me also checked out with a <1cm difference.i went through the device profiles (total station and GPS) and found that the antenna and mirror models are named somewhere in the settings. I believe theses settings wil automatically correct/add the right antenna/mirror height above the ARP of my pole.
I could check this myself by removing those settings and see if my measurements are off, but before i screw up my system i kinda want to know if my above ‘believes’ are true
Anyone here who can confirm?
All my gear is from Topcon (GPT9000 , Hiper+, FC-250 fieldbook).
OMEGA-ThundeR replied 3 years, 10 months ago 4 Members · 9 Replies- 9 Replies
Are you running the robotic instrument and the HiPer+ receiver together in a “Hybrid” configuration with Magnet Field software?
The standard prism that would have been the typical accessory to a GPT-9000 set would have been a Topcon A6R. That 360?ø prism is best described as a set of 6 mini prism in a ring mount. The series that followed the GPT-9000 would have been the QS series. The prism that is standard with those is the A7R, in which the prism is a solid piece of faceted glass. When I go through the profile settings in Magnet Field for a GPT-9000, the default prism is the A7R. If you are working with a Hybrid configuration as your post implies, and you have properly identified both the prism and the GNSS receiver, then the system knows what those values should be, but the height offsets assume that you are using the rod specified for the prism rod Topcon supplied with that instrument. If you are using a 2-meter rod, where the 2-meter mark is at the shoulder of the rod where the prism mount rests, then I do not see how the height values could be correct.
- Posted by: @jerrys
If you are using a 2-meter rod, where the 2-meter mark is at the shoulder of the rod where the prism mount rests, then I do not see how the height values could be correct.
You mean ‘Incorrect’?
My fieldbook uses ‘TopSurv’ software, but i think it’s somewhat the same as Magnet Field.
The prism i use is a Topcon A7 360. The 2 meter rod is used for both the prism and the Hiper+ GPS.
Both the A7 360 and Hiper+ are named in there respected profiles (GPS or Totalstation surveying).
In added image it shows my pole setup. ARP is my ‘Antenna height’ setting, my 2.00m rod. But i am worried i also need to correct the APC (with GPS) or the center of the prism in that ‘antenna height’ setting. So making my ‘antenna height’ 2.10m for GPS or 2.08m with the mirror.
If that is the case i don’t know why the Hiper+ and A7 360 are mentioned in my Topsurv fieldbook settings (and i whole list of different models also). I don’t want to stack corrections, thinking i need to set my prism height to 2.08m and my fieldbook adding another 8cm by default…
I did mean that I did not see how the system height assigned to the ARP of the HiPer+ could be correct if your measurement was to the base of the 360?ø prism. If you use the 2 m rod + whatever you have measured the height added through the A7R prism and however the adapter has been added to allow a 5X8X11 thread to accept the mounting of the receiver atop the prism, then your HR would be correct to the base of the mount on the bottom of the receiver.
Hybrid positioning in Topcon Software did not come along until they transitioned to the Magnet Field product. In Magnet Field, the ARP is set by the software adding the predefined height from the center of the ATP1 360?ø prism to the base of the mount of the receiver, also including the special adapter that Topcon has available.
How tedious is it to switch between GNSS and total station functions? In Magnet, the controller is receiving simultaneous data streams for both the robotic total station AND the GNSS receiver. When you are connected to the robot, the software uses the position of the GNSS unit to maintain the prism orientation, even though Magnet Field is reporting your measurement data based on the total station data stream.
- Posted by: @jerrys
I did mean that I did not see how the system height assigned to the ARP of the HiPer+ could be correct if your measurement was to the base of the 360?ø prism.
I don’t think we have the same idea of my rod setup. i’m not using any hybrid setup. Only one or the other. 2.00m rod and the Topcon A7 360 prism OR the Hiper+ GPS
Is all your above mentions information still right then?
All i kinda want to know is, do i have to correct the center of the prism and GPS in my fieldbook (rod length (2m) + center prism (8cm) or rod length (2m) + APC GPS (10cm)) or does the fieldbook (with topsurv software) corrects this information itself based on the setup for either case (using Totalstation with prism, or just using GPS stand alone). Both the exact antenna and the prism are mentioned in the fieldbook settings.
So, do i need to set my HR to 2.00, or 2.08 (prism) and 2.10 (GPS)?
I have a GPT9000 with the A7 360 prism.
I was supplied a graduated pole with this set which takes into account the prism half height, so that the graduated pole gives correct prism height with the A7 360 prism.
The pole I was provided with my Hiper V has correct height for the receiver, with the graduated measurement relative to the ARP.
The respective heights will not be correct if they are interchanged.
I misunderstood what you were asking. Topcon has promoted a “Hybrid” option for the last few years whereby the system is simultaneously connected to both a GNSS receiver and the robotic instrument. The wording of your initial statement made me think that was what you were doing, but that option did not appear until the 2nd or third released version of their Magnet Field software. I did not know how you’d have been doing that with the components you mentioned and TopSURV, but I read your initial post as though you were.
Now that I better understand that you are using either the robot or the GNSS receiver, not both together, my answer is conditional.
If the rod you are using is the type of 2 meter fixed height rod that has been typically supplied with GNSS equipment for years, the measurement of a vertical offset as you’d normally do for an RTK rover rod of 2 meters is expected to be to the shoulder of the rod at the base of the 5/8X11 thread. The GNSS antenna profile accepts that entry as being the rod height and adds in the vertical offset to the ARP behind the scenes based on what receiver you’ve selected in your receiver settings.
If you are also using this type of rod with the 360?ø prism, you would need to add in the distance from the shoulder to the rod to the center of the A7R prism. I just measured the distance from the bottom of the adapter that is the base of the A7R prism and it appears to be 75 mm. Therefore, if your rod that you use with the robot is a two-section, two-meter fixed height rod, you’d need to make your height of rod 2.075 meters to get to the center of the prism. That is not quite all the 10 cm difference you are looking for, but it is most of it. If your rod is the robotic rod that you’re also using with the GPS receiver, then the graduations factor in the height of the center of the glass above the bottom of the adapter on the prism assembly.
Jerry,
Perhaps he is talking about the graduations on the lower rod face of a 2m GPS pole like this. These are not designed to not work your Total Station and Prism. Topcon now uses the ATP2 prism, with a graduated pole (like this) that is calibrated to show the height of the prism. But this still doesn’t have lower graduations like a GPS pole. Some prism poles have an adjustment rod at the top to let you calibrate the height relative to prism.
Lee, I thought of that, but wanted to deal with one issue at a time. If he is using a GPS rod for the robotic prism as well, that would give him an automatic height bust but the distance I measured from the base of the adapter on the A7R prism to the center of the glass would not account for all the difference he said he was seeing.
That is one of the problems with assumptions. Their results and consequences often show up in the most unexpected places…
Things are really starting to make sense now.
Using 2 wrongs did seem make it right when i do all the measurements myself, but now that i used reference points (reflectors) from a third party the error was clear when i measured the controlpoint with my 2.00m HR and was about 10cm off. Funny enough they corrected that height before by about 2cm (dunno why), so with the 7,5cm correction of the prism, that pretty much clears all the error in that measurement.
it’s also the first time i used reflectors, i normally use the GNSS/GPS to make a couple of basepoints and use those reference points to set up the totalstation.
Posted by: @leegreenJerry,
Perhaps he is talking about the graduations on the lower rod face of a 2m GPS pole like this. These are not designed to not work your Total Station and Prism. Topcon now uses the ATP2 prism, with a graduated pole (like this) that is calibrated to show the height of the prism. But this still doesn’t have lower graduations like a GPS pole. Some prism poles have an adjustment rod at the top to let you calibrate the height relative to prism.
i do have an rod like that, but i kinda don’t want to walk around with 2 rods. Now i know i have to correct the prism center on my 2m fixed rod.
Do have to check if i use the correct graduated rod, got one in my van (at garage) and one in the office, but the one in the office is 1,5cm off from the measurement given. (i.e. says 1.50m at the measement point, using a tapemeasure its 1.485 from the base to the center of the prism).
Thanks all!
Log in to reply.