How to find more RECENT benchmarks?

[planewood]

I downloaded the benchmarks from geocaching.com for my zip code (77449) and have tried to find about 10 of them. All were gone or buried under recent construction. I went out with my 60cx with an external antenna on a 10' pole and only during times of low HDOP, so I know I got fairly close to the stated positions. With all the recent construction in my area I know there has be be some visible somewhere, but where do I find coordinates for them? Is this info kept at the county or state levels?

 

ps - the last one I checked a cable company had just dug a 4' deep ditch across it's location! I can see where it was in an aerial photo taken 8 or 10 years ago.

[+PFF]

Hi, Planewood. Welcome to the hobby! Later, I want to hear more about your amplified antenna and 10-foot pole. I use the same configuration. But first, let's get you to a database where you can find the most recent reports.

 

Go to

www.ngs.noaa.gov

 

At the top of the home page, click DATASHEETS. This will take you to a series of menus where you can view and print datasheets using several selection methods. Personally, I like the Interactive Map.

 

Since you're just getting started, pick a couple of marks that have been found, recently--either by professionals (on the NGS site) or by amateurs (on GEOCACHING.COM). Retracing their steps will give you the practice needed to go after the difficult marks.

 

There may be additional database resources available, depending upon where you live. Pass along your state and county, so if somebody has 'inside' information, they can share it.

 

I'm certain others will join this thread later today with tips/suggestions. I'll start with one of the most important. "Don't Let The GPS Receiver Be Your Only Tool".

 

During the last six feet of the search, you will need to rely heavily upon the printed description. Let's face it, even with your additional equipment, the resolution is still a few meters wide. So try to visualize how things looked back in 1980 when the description was written.

 

*Is the stump of the 24-inch Oak still visible?

 

*Has a wing been added onto the church building?

 

*Did they add lanes to the highway, and if so, where was the original centerline. Or, for that matter, where was the highway before they moved it? (EZ1208)

 

*You may not see the referenced driveway. In the city, is there a cut in the curb? In rural areas, is the culvert pipe still in place in the ditch? (EZ4442)

 

*Has the gas station been torn down? If so, is the pump island gone? (EZ1850) Or is it still there and being used for decorative purposes? (EB3653)

 

Identify as many referenced objects as possible and measure with a tape. This is especially true if the published coordinates are SCALED, because the horizontal position may be off by hundreds of feet. (ADJUSTED coordinates are precise.)

 

A note about the NGS website. The coordinates are in Degrees, Minutes, and Decimal Seconds. On GEOCACHING.COM, we use Degrees and Decimal Minutes. The conversion is easy--especially with on-line calculators. But it's important to keep things "apples and apples". Pick a format you like and adjust all sources to the format you're using in the GPS unit.

 

Again, welcome. If you see something not covered in the FAQ ("Read This First") section of the website, feel free to ask. The experienced guys and gals in this forum have been a great help to me, and I'm certain your experience will be the same!

 

Best regards,

-Paul-

[holograph]

You seem to be near a major high growth urban area, and that spells disaster for many benchmarks. I did a search on a 5-mile radius in the area, and out of 75 marks that are located there, 56 of them, or about 2/3, were reported not found recently. Here are some marks that have been reported found in good condition within the last few years. Your could start by trying to find some of them.

 

As PFF noted, you need to go by the description. The latitude and longitude only get you to the immediate neighborhood. Since most of these marks were intended for elevation control, not geographic control, the published location is only a hint.

 

Also, many of these surviving marks are along a railroad track, so they may not be accessible to you. If the railroad is active, the company will usually strongly discourage trespassers, even to the extent of arresting you. Be careful.

 

AW0261

AW0267

AW0269

AW0270

AW1864

AW1877

AW1883

AW1885

AW4499

AW4547

AW5446

AW5447

AW5448

AW5449

AW5450

AW5453

AW7100

AW7102

[planewood]

Thanks PFF!

 

I went to the noaa site and downloaded those with horizontal control within 5 miles of my house. Of the 10 or so in the list, only one (AW1864) was reported found (2004). I looked it up using GE and it appears to be very easy to find. The rest were reported not found.

 

GE appears to be registered to within 2'-3' at the site of AW1864 (2' SW of a power pole). I'll visit the site shortly and see what I can see.

 

My antenna is atop a 10' PVC pipe. I rigged up a carrier on the pole at eye level for my 60cx. I usually take a Trimble chart with me when I'm out tramping around. Seems to help. The antenna magnetically connects to a 2" steel washer on top of the pole. I've wondered if a larger surface plane would help. Maybe at least to shield ground reflections?

 

I bought my GPS to find the corner stakes of some property I own up in NE OKLA. The property is not fenced and was last surveyed about 30 years ago. I was able to find all the rebar used to mark the corners. The area is heavily timbered and the 60cx and the antenna really helped. I found the pin for the starting point of the survey then calculated the other lat/lons using the old survey bearings. I am not a Geocacher. At 65 yrs old, I try to minimize my treks in the boonies!

[mloser]

And don't trust your GPSr, even WITH the cool antenna, unless the mark is stated as being "adjusted" as opposed to "scaled". Scaled marks, which are normally used for vertical control only, got their coordinates by being measured on a map. They could be as much as 600 feet away from the coords on the datasheet. Use your GPSr to get you close, then read the datasheet and look for the mark using the description, e.g. AW4547:

61 FEET NORTH OF THE CENTER LINE OF HIGHWAY, NEAR THE SOUTHWEST END OF A DIRT RESERVOIR, 102 FEET EAST OF A HUMBLE PIPELINE SIGN, 1 FOOT NORTH OF THE RIGHT-OF-WAY FENCE, 1 FOOT NORTHEAST OF A METAL WITNESS POST AND AT TEXAS HIGHWAY DEPARTMENT STATION 662 + 31. A C AND GS BENCH MARK DISK, SET IN A 12 X 12 IN. CONCRETE POST WHICH PROJECTS 5 INCHES ABOVE GROUND

. I would immediately expect two things to be missing from this description-the witness post and the highway department station sign. In fact, I might well expect ALL of these things to be missing, but there might be enough evidence of some of them to help you search--for instance, the centerline of the road may be able to be determined, even if it was widened, the pipeline might still exist (it IS on the topo) even if the sign isn't, and there might be evidence of the reservoir.

Use whatever resources you can find--I use the topo link from the GC.com page, Google, Google Earth, USAPhotoMaps, and anything else I can find. You can't go into the field with too much information.

 

Matt

[planewood]

Also, while new to this part of the Groundspeak forums, I am not new to the 'arts' of geographical coordinate systems or of benchmarks for that matter. I just didn't know where to go online to find more of them. Now I do! Thanks!

 

I worked for a major oil co. for 35 years writing geographical mapping and geo-statistical software in the exploration dept. I'm quite familiar with things like 'adjusted' or 'scaled' benchmarks. Also quite familiar with the jillions of different types of coordinate projection sistems. Having been retired for about 8 years, I'm finding a lot of the significant details of all the above are starting to blur a little, however.

 

I have taken several college level surveying courses over the years and have had training with the more sophisticated differential GPS systems. I decided to spend a little more of my kids inheritance last year to purchase a GPSr for myself. For what I needed to do, the Garmin 60cx has been a jem!