Translation to SPC (GPS and FG2005)

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Posts: 139
Joined: Sun Nov 24, 2002 6:45 am
Location: Temecula, California

Translation to SPC (GPS and FG2005)

Post by ianw2 » Tue May 03, 2005 7:07 pm

OK. Here’s my normal job flow for a boundary situation.

1) Pre-calc job from record maps, deeds, documents, etc. Pre-calc coordinate system is based on an origin point of N/E/El of 20,000/50,000.0.

2) Hit the field. Find a monument I can identify as being a particular one of record from my pre-calcs or a find a good high place to set up my GPS (Topcon HiPer Lite) base.

3) Find a second monument to do a localization on.

4) Use the localization to stake out additional monuments from the pre-calced positions.

5) Set up my three Thales ProMark2s on found monuments surrounding the site.

6) Do 10 to 15 minute static sessions on additional found monuments.

7) Post-process the files and put everything on SPC values.

A perfect example of this kind of work is the following downloadable file:

The clients property is an aliquot portion of a section, nominally 10 acres. There are three maps in the same Southeast Quarter of the section. I need to be able to locate appropriate points to define the client’s parcel. I will be laying out aerial targets tomorrow and need solid 3D SPC values on the points I set for aerial targets.

This job is a perfect example of what 90% of my practice is. I specialize in boundary and topo. For those wondering why I have a 10 acre parcel flown: because my photogrametrist can do the job from the air cheaper than I can on the ground for parcels over 5 acres. This one is quite rough (although not nearly as rough as many others).

In this case, I set up on a random point (100) at the top of a hill. I found and shot Pt #10 as Pt# 1000 and Pt # 44 as 1044 (this was a bear of a job to get figured out on the ground).

I calculated the translation parameters based on the pre-calc’d points v. the shot points.

In the “Data Manager” / “Coordinate Database” screen, I translated point 1-87 to the GPS derived points already on SPC California Zone VI – NAD83.

All the points moved just wonderfully. I then went to stake out Pt #8 and found that I was some 2 million/6million feet away! Apparently, it managed to move my localization based on 100, 10/1000 and 44/1044 as well. I quickly figured that I had to go back and “re-localize”. After that, things went rather well.

The only other problem I had was that the DXF file with all the line work I had pre-calculated stayed behind back at 20,000/50,000. As you may surmise, with the number of points and the pre-calculated breakdown of the quarter section, having the line work would have made things a lot easier, today!

Is there a better way to move the precalcs up to the GPS measured points? Is there a way to move the DXF file as well?
Ian Wilson
Ian Wilson Land Surveying, Inc.
Temecula CA 92591
(951) 684-1044

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