Perplexing Day, Filed Maps and GPS Problems
Not a major project but simply a swimming pool construction plan survey, I work for the pool installer.
I start out with PQ deed and filed map as referenced in PQ deed. PQ is last lot to West on Section A of development plan. Deed has minor variations from filed map and no comment as to why. Gather adjacent lot West deed and next section of development as referenced in adjacent deed. Filed map has notes it replaces a prior filed map and I find PQ deed is in agreement with that map information . OK, I can live with that certainty for a pool plan, were I doing an actual survey I would go to the courthouse rather than do on line research. Plot out PQ and adjacent lot each side and head off to the field for reconn and GPS.
Check out the frontage for 2 lots each direction and get no sound, so I set mag in pavement (no curb) for an OPUS observation near SE corner. Set a mag in common driveway near SW corner for an L1 reference point. I am blocking the mailbox and as I set up the mailwoman arrives and I move Jeep into driveway. Finishing setup as PQ mom arrives and she waits for me to get out of driveway. She has no idea about corner pins, so I proceed with locator to back yard. All quiet on PQ corners. Neighbors to East had no recollection of corner pins. Mom to West comes home and thinks she saw one years ago in back yard. West dad comes home and yes, at the NW rear is a pin behind the shed. I grab locator and walk back, 3/4″ rebar 1″ up. As I flag it I recall that this is an angle point in filed plats, check plat and see a circle at corner but no calls. I will now get the previous plat. As I am putting locator away another neighbor walks by and asks what I am doing. I ask him where he lives and if he knows of any of his corner pins. He responds yes, because he had his lot surveyed. I ask him to show me some and we walk two lots West on far side of street. He shows me 2 old mag nails in pavement which appear to be on sidelines extended. He volunteers to show me his map and I ask if I can borrow it to copy. He says he can do better and brings up a 2011 pdf on his phone and shows me a mark up of part of the Filed Plat. He emails it to me on the spot. Back in the office the markups are in red ink and show 11 pins found, 1 metal detector reading in a driveway and 4 mags set and offsets from corners. He in fact owns back to back lots fronting two streets. This like gold to me. I set up to 2 more L1 units on those mags under trees but it is just for orientation to get all filed plat info overlaying my orthoreferenced photo.
So I get home and download GPS and send off 2 hr 20 min file to OPUS. Worst data I have ever seen: 0.055m northing and 0.100m easting, but ortho height was 0.034m. 67% of observations used and 36 of 63 ambiguities fixed. I can look North from the PQ and see the site where LUMT CORS sits, but that CORS was not used. I will download it and solve myself. As to my L1 receivers, positions were ridiculous, did I mention there were 50 year old street trees. L1 to L1 vectors used only 3 or 4 common satellites, so I excluded all L1-L1 and got relative position precision’s under 0.010m. When I get back out there I can locate all 3 (plus any referenced pins I dig up) from my OPUS setup point and need to set 1 traverse in the back yard for the 3/4″ rebar and the PQ pool area. Not in a rush as it is still snowing. Every setup leg point that was in lawn and not on pavement came out with a 3″ clump of sod frozen to it when I broke down last night.
Today I will break my OPUS into 2 OPUS-RS files, plus see if OPUS picks any better CORS.
Perplexing to start, but hey, this is what makes surveying fun.
Paul in PA
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