Jump to content

Coordinate Change Curiosities


andylphoto

Recommended Posts

I haven't been very active benchmarking for the past year or so due to life circumstances--spending a lot of time expanding a business, buying & improving a house, etc. One day I will get back into it when I have more time, but for now, I have very limited time to devote to it.

 

I have been doing some "drive-by" benchmarking, where I'll pick out a single mark very close to a road where I'll be driving by anyway, and try to find it. My other activity is "armchair benchmarking," which for my purposes consists of perusing datasheets & maps while at work, to facilitate the "drive by" activities, look for potential targets, and check in on previously recovered marks.

 

I found two things of interest this morning I thought I'd share. The first is that I discovered several stations where I had previously submitted HH2 coordinates for scaled marks. The Michigan DOT has since done GPS observations on at least three stations, and NGS has now published adjusted coordinates. Two are along a major highway, but RL0211 got my attention as it is a bit off the beaten path. Set in 1934, then my 2007 recovery, M-DOT in 2009, then adjusted earlier this year. This was an older recovery, where I had included the coordinates in the description. I was pleased to see my posted coordinates were within a tenth of a degree each way, and its nice to see these older marks getting used and upgraded.

 

The other thing I noted really has me scratching my head though. I looked at a number of marks that I had previously searched for. I found several with no recent recovery reports, but whose coordinates had been upgraded. For example, here's one I recovered two years ago, and had submitted HH2 coordinates. Those have now been upgraded to HH1, but there is no recovery report since mine: RK0248

 

Even more puzzling are several with NO recovery reports. Several of these marks I have spent time searching unsuccessfully for. I did not report, wanting to go back with time to do a more exhaustive search before submitting a not found report to NGS. For example, RL0213 has no recoveries since 1934, and I was not able to find it based on the description, even with the added tool of having "adjusted" the coordinates based on the topo map location. There are several like this with no recent recoveries (or only a couple of not founds) whose coordinates have been upgraded to HH1. I haven't gone back to look to see if someone actually went out and found these marks that I couldn't, but it just seems odd that there would be this slew of coordinate upgrades with no recovery reports. Any thoughts?

Link to comment

Andy, you didn't get the top-secret memo DaveD sent out to us about this? You must have been away for awhile. :lol:

 

Seriously, I have been seeing a lot of local marks getting updated HH1 coordinates, with many of these being reference marks for triangulation stations. I am assuming that since the stations had adjusted coordinates, that you could use computer programs that will give you accurate numbers from the measurements and compass directions to achieve this.

 

However, this is just a guess on my part, and I'm sure we'll get the low-down shortly.

Link to comment

No, I must have missed the memo!

 

These were all scaled marks. The "adjustment" was my own--adjusting the scaled coordinates in my GPS software to match the location of the mark on USGS topo maps--I've had good success getting to existing marks when old references have been removed.

 

The ones I found, I had submitted HH2 coordinates for. Ones I didn't find still had the scaled coordinates in the NGS database, but have now been upgraded to HH1, with two decimal places in the seconds. That even eliminates the possibility of my accidentally submitting coordinates in error--coordinates I submit only have one decimal place.

 

It just struck me as odd that if someone actually did find some of these old ones with no recoveries and no current references and took the time to take GPS observations, they wouldn't have submitted a recovery report.

Edited by andylphoto
Link to comment

Andy -

A few years back Dave had told me that he will look at recoveries here on GC, and if a station has a HH2 accuracy, and another found log is posted with coordinates (can't remember if the he mentioned the coords had to be visible in the GPS or not) backing up the first set of HH coords, he'll upgrade the accuracy to HH1.

 

Now this isn't what happened to RK0248, because noone's submitted a recovery here for that station either.

 

--me.

Link to comment

Andy -

A few years back Dave had told me that he will look at recoveries here on GC, and if a station has a HH2 accuracy, and another found log is posted with coordinates (can't remember if the he mentioned the coords had to be visible in the GPS or not) backing up the first set of HH coords, he'll upgrade the accuracy to HH1.

 

Now this isn't what happened to RK0248, because noone's submitted a recovery here for that station either.

 

--me.

 

Interesting...thanks for that info. I came across another good example of what I'm talking about...

 

Here is the "original" geocaching copy of the datasheet for RK0138. It shows the station as a scaled mark, a Not Found by Alger County, and another Not Found by a former Michigan NGS advisor, who recovered most of the marks in this string back in 1998 before they removed the rail line. The current datasheet for RK0138 shows no additional recoveries, but upgraded coordinates, slightly different than the scaled coordinates.

Link to comment

The HH1 positions for both RL0211 and RK0248 were harvested by me from the historic records of the U.S. Geological Survey (USGS). While USGS never officially submitted their data for inclusion in the NSRS, NGS does maintain a nearly complete collection of their old horizontal and vertical control data. The positions that they determined for mapping purposes are of at least third-order accuracy and certainly better than the scaled values. Along with positions provided from this site (as foxtrot xray noted) over the past two years I have been capturing these data so it can be perpetuated before I retire. I regret that when I go no one at NGS will even know we have this data and how valuable it can be. I have also been computing HH1 positions for Reference Marks (RMs) as LSUFan noted. Since the datasheets for most triangulation stations provide both the azimuth and distance to RMs it is a rather simple process to compute the position using the FORWARD utility we have in the NGS geodetic tool kit. Like the USGS data these values are legitimate and superior to scaled positions. Since no one is actually visiting these stations there are no corresponding recovery notes to post. The HH1 post currently leads one to believe that someone actually made some sort of GPS observation at the station and therefore there should be a recovery. We will be changing the designation of HH1 to read something like "The horizontal coordinates have an estimated accuracy of +/- 1 to 3 meters and were established by differentially corrected hand held GPS observations or other positioning techniques of comparable accuracy."

Link to comment

Thanks for that information Dave, and a big thank you for hanging out here and answering our questions! That's very interesting--that's got to be a huge project for you! I get overwhelmed sometimes just looking at the marks in my county that I haven't recovered, not to mention the other 82 counties in michigan and 49 other states! :)

 

Even as an amateur benchmark hunter, this will make my job easier when I do get the opportunity to go out and do some serious searching. Like I mentioned above, I've been in the habit of adjusting my own coordinates with some topo map research on my computer, and using NGS Forward for reference marks. Looking forward to the time when I've got a lot more time to go hunting!

 

I, for one, appreciate the work that you're doing, and your dedication to keeping things up to date and easy to use!

Link to comment

While USGS never officially submitted their data for inclusion in the NSRS, NGS does maintain a nearly complete collection of their old horizontal and vertical control data. The positions that they determined for mapping purposes are of at least third-order accuracy and certainly better than the scaled values.

 

Dave, that's extremely interesting. If I'm understanding correctly, the USGS didn't really do anything specifically to get their information into the NSRS..... but it was the NGS who really "bluebooked" all the USGS marks that are in the NSRS?

 

For some reason I thought that the other agencies, after meeting the NGS bluebooking requirements, sent their info to you to be specifically included in the NSRS. Now, I see where you even do more things behind the scenes. It's like I said before, you are a ninja. :ph34r:

Link to comment

The "Blue-Booking" process is very rigorous and that is not exactly what I do with all the old USGS data. As some on this board are aware, the USGS information is still in paper format. For many years when they ran horizontal control traverses to support their mapping efforts they would often tie some of our (USC&GS/NGS) bench mark disks so they would have our vertical control and their horizontal information on the same point. When we created the database that supports NSRS these bench marks were given scaled positions because we did not have the USGS observations "Blue Booked." When we created the HH1 & HH2 position categories several years ago the intention was to have a way that we could improve the recovery information for bench marks from the many users of hand-held devices, and this has been a success. A couple of years ago I looked at all the historic USGS data we had in our archives and figured that their old NAD 27 third-order data was certainly equal to if not better than the intention of HH1. Since that time I have collecting their data by region and transforming their NAD 27 values to NAD 83 using the CORPSCON transformation utility and then our program DSWORLD to submit those updated values to the NGS database. These updates are typically updated within a week of the first of each month. Between positions that I harvest from this site, the USGS data and computing values for RMs I typically update about 1,500 scaled positions each month. Hopefully I will be able to complete the transformations of the USGS data during the next two years before my currently planned retirement date. As I mentioned previously there is almost no one at NGS who even knows this data exists or how to read it anymore.

Link to comment

Just did some more checking, and both DaveD and the Michigan Department of Transportation have been busy! I had a file on my computer with eight marks I recovered in the fall of 2009. All were scaled marks where I had averaged coordinates for submission, but hadn't sent them in yet.

 

Of those eight, four had been occupied by M-DOT and now have adjusted coordinates, and two have been upgraded to HH1 by Dave. Wow.

 

Interestingly, all of the now-adjusted marks I recovered in September-November and submitted recoveries. M-DOT actually occupied the marks in June, but didn't submit recovery reports until much later, but their recoveries are listed before mine because of the dates. :) I think PFF had that happen once on a string of marks down his way too.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...