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Public Land Survey Corner Database
I am brainstorming/researching for a GIS database for the Public Land Corners that we are responsible for maintaining, documenting etc. in Jefferson County, Oregon.
I have looked around at a few similar data sets on other websites, County, State etc. Some are better than others. Specifically some lack detailed data, links to reports or images etc. Others simply have a poor interface for online users to access data.
So far I think I like this page the best…
http://www.wsdot.wa.gov/monument/
I would like to see a report generated that shows active links to corner reports, images, gps obs files if available, etc.
If you have experience constructing such a data base I would love any advice you could give.
Otherwise if you use sites like this frequently I would like to hear what you like, what you don’t, suggestions for improvements, desired features etc.
Thanks in advance for your input.
P.S. here is a brainstormed list of data I would like to see in a report
- County Index Number
- BLM Index Number
- Monument Type
- Latitude
- Longitude
- Ellispoid Height
- Orthometric Height
- X(ECEF)
- Y(ECEF)
- Z(ECEF)
- Plane Coordinates (& Projection)
- Projection for Plane Coordinates
- Ellipsoid Model
- Geoid Model
- Horizontal Datum & Epoch
- Vertical Datum
- Year Measured
- Data Source (if not measured)
- Positional Accuracy
- Confidence Level
- Equipment Used
- Observation Date(s)
- Observation File(s)
- Photos
- Corner Restoration Cards
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13 Replies
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Check out the Utah site:
Zoom in to T13S, R4E, Sec 34, SLM. Look at say the N 1/4 of Section 34. Click the purple dot. Then to the right side you can open the Tie Sheet. A pdf file with most of what you want comes up (look in the attachments for photos, OPUS, etc.)
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Excellent, thank you!
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Kevin, I can appreciate the struggle you’re having trying to ensure the integrity of your PLSS DB. Below are some suggestions for your consideration:
1) In addition to Monument type the report should include any stampings on the mark.
2) If the horizontal datum is defined then specifically asking for the “ellipsoid model” is redundant since it is part of the datum definition. For example: NAD 27 is defined on the Clarke 1866 ellipsoid while NAD 83 is defined on the Geodetic Reference System 1980 (GRS80) ellipsoid.
3) I’m also not sure what you get from “Equipment Used” as long has the positional integrity is stated. I can see where it might possibly be somewhat useful to surveyors in the future as to how the position/elevation was determined. If that is the case then it would be just as important if not more so to provide information detailing what procedures were followed to obtained those values (e.g. instrument/rod calibrations, number of directions turned, met observations taken and applied etc.) Just knowing that someone performed some undefined number of GPS observations with a specific type of receiver doesn’t really say much.
Good luck
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Thanks for the reply, I appreciate it.
1) photos of monuments will be included. Marks on caps from previous reports are documented I the corner records so that is covered.
2) ellipsoid is not needed for plane coordinates if the datum is defined, I agree. However a lat, lon and ellipsoid height should also state the ellipsoid model used if available. If it is unknown it will be stated as such. We have a wide variety of data sources for this corner database so I want to be able to include any data available to me in the database.
3) equipment used could have been better stated by me. Perhaps method used is a better field… RTK, static GPS, convential etc
Thanks again. So far there have been no difficulties… but we haven’t started building the database yet!
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Once the horizontal datum is stated then the ellipsoid is given by definition, regardless of whether the coordinates are expressed as State Plane, UTM or lat/long/EHt. All horizontal datums are defined by 8 primary parameters – 3 for the origin of coordinates, 3 for the orientation and 2 for the ellipsoid (typically the semi-major axis (a) and the inverse flattening 1/f).
Without knowing the mechanism for how people will add information to this data base I would hope that there would be prohibitions to allow anyone to submit a coordinate and/or a height without providing at least the datum of reference. IMHO a coordinate without supporting metadata is worthless data.
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I usually submit an OPUS Report with my corner records. If RTK then I submit an OPUS report for the base station and then the dX, dY & dZ of the vector to the monument. Also lots of pictures, field observation report, narrative, GLO notes. Just about anything can be put into or attached inside of a pdf file. I’ve even submitted scans of previous surveys if that is part of the evidence of the corner location. From this report everything needed to put into a database can be derived. Also a nice vicinity map could be a kml file (haven’t done this yet but thinking about it). Hey, we have the technology why not use it.
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Realize that some of the data available is historical. You get what is there and no more.
Like I previously agreed… If a horizontal datum is defined ellipsoid height is unnecessary… But what about
44d56’34.56789″ N
121d09’34.76543″W
2345.67 El HtDoesn’t do you a bit of good without an ellipsoid model or the corresponding horizontal geodetic datum.
Thanks again.
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I totally agree.
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> Once the horizontal datum is stated then the ellipsoid is given by definition, regardless of whether the coordinates are expressed as State Plane, UTM or lat/long/EHt. All horizontal datums are defined by 8 primary parameters – 3 for the origin of coordinates, 3 for the orientation and 2 for the ellipsoid (typically the semi-major axis (a) and the inverse flattening 1/f).
>
> Without knowing the mechanism for how people will add information to this data base I would hope that there would be prohibitions to allow anyone to submit a coordinate and/or a height without providing at least the datum of reference. IMHO a coordinate without supporting metadata is worthless data.Thanks for the reply on this. I have been mulling your statements and suggestions over the past few days.
I agree that new submissions should have the datum and hopefully epoch defined.
In at least some sense I disagree (pending my interpretation of your statement and my further explanation) with your statement regarding a coordinate without supporting metadata. I will say that if my primary objective was to simply establish and maintain a geodetic survey control network I would be in 100% agreement.
However, another objective of this database would be to provide data on previous recoveries of original evidence of PLSS corners. In this sense that “naked” coordinate could turn out to be priceless. Sometimes these positions are only documented with a hand-held GPS receiver or a mapping grade GPS receiver. Older documents might show a NAD27 SPC coordinate etc. I think this is valuable information for a retracing surveyor. I would specify the quality of these positions as “UNKNOWN”. My hope would be that a prudent land surveyor would not use these positions for control, but rather as a starting point for corner search and recovery.
The source of the position would also be necessary information in the database… e.g. GPS observation (and obs files, OPUS report), GCDB, hand-held/mapping grade GPS coord, SPC from record document, etc.
I would prefer high-quality positions throughout the database but in reality I have some pretty small populated areas in my county and not a lot of funds for a GNSS campaign to tighten control county wide. The existing GIS in some areas is accurate due to a GPS campaign and LDP of sorts in the early 90s. However large portions of the county GIS mapping are little more than cartoons. I would like to establish a framework for best positions available to be used not only for the county surveyor’s database but also as control for the county GIS. Long term I think that archiving all of this information will be valuable for our county.
If you have further thoughts regarding this I welcome your critique/suggestions.
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Yeah, it would be better to know 100 corner positions to within a foot than 10 to within a centimeter. Even 10 feet should suffice for surveyors. If you can’t find a marker within 10 feet of a coordinate maybe you should look into another line of work.
I think the best method is to have the database info that makes a GIS work and display the location on a map. Then the database could have a pdf or pdf’s with all the supporting data to prove the corner. I attached a Trimble .DAT file to a pdf today. You can open the pdf, open the attachment and save it. Then you can submit the file to OPUS and get a solution. You can attach just about any file inside a pdf. CAD files, photos, GPS observation files, data collector files, text and spreadsheets, etc.
I think the days of plats on paper and Mylar are about over. It should have happened before now.
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I really like that site. After some further research I think it might worth my time to figure out how to populate my database with OPUS-DB on new corners as they come in. This would be a huge benefit in my view.
Thanks again for all of your input on this.
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Wow what a project! It took the BLM GCDB 30 years to complete. That’s with 5 to 8 surveyors and 2 to 5 techs working. One of the reasons it took so long was the rigorous in-depth work in each twn. GCDB went thorough several computational changes. From compass rule adj. of the best data and force the rest to close to it, to a Least Square Adjustment (GMM). GCDB is a fluid concept, it can be readjusted when new data is available, but readjusting is almost as rigorous as the initial adjustment. GCDB data has a lot of what you want, surveys used, control used to adj. the twn. , Lat, Long and error ellipsoid for each pt. Good luck with this.
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