California Surveyors Forums

I just downloaded a fairly recent (2013) parcel map in Ventura County where the map is tied to two CORS stations from one monument. The control diagram shows the CORS stations with a line between them and from each CORS to one of the Found Monuments on the map. The notes give the Lat/Long & Northing and Easting of each CORS station and the Convergence angle at each CORS. Each of the three lines in the control diagram is labeled with the bearing only. Hmmm. So two bearings to the nearest second from CORS Stations miles away are supposed to get me to the found monument that ties this map to state plane? I wonder what my error ellipse on that computation would be.

Among other things, no combination factor info is given to go from grid to ground and none of the required statements to show compliance with the PRC sections are on the map.

so is the map in grid or ground? PRC only apply's if in Grid. I don't believe there is a requirement if the mon's are just being used as a BoB.

Typically these requirements to show ties to stations with SPCs are for use by the GIS folks to drop the new linework into their system with a minimum of fuss ...

They show SPC on the CORS stations. Showing the SP coordinates triggers PRC requirements, not whether the map is computed in grid or ground distances. The map does not state grid or ground, but how do you get from the SPC's on the CORS stations to the other points shown on the drawing without a single distance on the control tie lines. Sketchy work, at best, for me.

using the protected terms trigger the requirements to follow PRC, not just state plane coordinates, but if you want your GPS surveying to be retracable, then you should looki into the PRC

Bear in mind I am playing devil's advocate with this answer.
A geodetic tie to the nearest second - 1 arc-second is a foot in 40 miles.
Are the CORS within 40 miles?
Depending on the geometry, the bearing-bearing error ellipse may be a foot to maybe 5 feet.
I firmly believe I would find the monument if my search area was within 5 feet.
I seriously doubt a long-range geodetic tie would be the best available evidence to reset a missing corner.

I suggest that you contact the county surveyor that signed the map and ask their opinion.

A little background on the parcel map, which I assume is the City of San Buenaventura parcel map filed in Book 70 Page 1-3 of Parcel Maps, County of Ventura. When first submitted, this map showed an assumed basis of bearings between 2 found monuments from a record of survey. When the map checker asked why the bearing was 4 seconds different from the RS map, it turned out that it was actually based on CCS83 (2007.00), and the basis of bearings statement was subsequently modified to indicate that. The map doesn't show ties to the 2 CGPS stations, it simply illustrates the basis of bearings. The map uses only ground distances, and does not establish new CCS coordinates at all; it does show published lat/long and calculated CCS coordinates for the CGPS stations.

Wayne Battleson
County Surveyor
Ventura County

PRC 8813.1 - After December 31, 2005, any survey that uses or establishes a CCS83 value shall meet all of the following requirements:...see additional language in the code here: http://www.leginfo.ca.gov/cgi-bin/displ ... =8801-8819

PRC 8813.3 - After December 31, 2005, when a survey that uses or establishes a CC83 value or values is shown on any document, the station or stations to which the CCS83 value or values and the published or stated accuracy or accuracies of that reference station or stations shall be shown also on the document.

PRC 8813.2 - after reading 8813.3 and showing an accuracy as required, now it seems 8813.2 applies. (This statement is wrong - 8813.2 applies when establishing new CCS83 coordinates.)

PRC 8815.5. When CCS83 coordinates are shown on any map, corner record, or record of survey, a mapping angle, combined grid factor, and the elevation used to determine the combined grid factor shall be shown on the map, corner record, or record of survey for at least one representative point.

(Any emphasis is mine.)

As soon as you show or use CCS83 coordinates certain info needs to be added to the final documentation (map, CR, RS, etc.).

Please note - The purpose of the OP was not to call anyone out specifically, just to note that, IMO, the law is being misapplied in many places. Informational only.

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