GPS and surveying

[Code54]

I have a question regarding surveying and how they write the plat maps. The Plat map of my property has some sort of longitude and latitude markings (I think they are at least) but I can not line them up with my GPS. I am guessing this is a different datum or way of expressing the position of property lines. The pins are all in on the property but several places it is very hard to see them (due to contour of the land) and I figure if I could use the map marking I could easily follow the lines. An example of the marking are:
N 18* 37’00’ E
S 66*39’12’ W
The * is supposed to be a degree symbol
Any idea how I can set my GPS so the readings would be the same as this map? Is there a certain Datum surveyors use and is it even called a datum?
Thank you

 

[ronjhall]

I do not know what format you location is in. But here is a converter when you figure out the format. Click Here

 

[Code54]

Thanks for the site Ron - saved that in the Favorites! Any idea how I can figure out how they wrote it in the orgional map? Is there something that is a give away to the Datum they used? This is all new to me so sorry for all the questions but thank you for the help.

 

[BillG_in_TX]

Code 54,

I think those readings indicate the bearing from one pin to the next. For example the heading indicated in your first example would be 18 degrees and 37 minutes east of due north. The second example would be 66 degrees and 39+ minutes west of due south. Is there a distance indicated as well as a bearing?

edit - Here's an earlier discussion on using your GPSr to assist with mapping your property.

 

[johnday]

Scott; BillG is right. The confusion seems intentional by the surveyors, in other words, it's made difficult to decipher, so you have to have them come out at your expense. /forums/images/graemlins/frown.gif I don't know if what I said is true or not, but it seems that way. /forums/images/graemlins/confused.gif I had better luck using a compass when walking my property before I bought it. GPS that are available to the general public usually have an accuracy of +/- 20 feet. Not accurate enough for me at least. What you could do if you have questions about the datum, call your township or county office, and they should be able to get you on the right track. /forums/images/graemlins/grin.gif

 

[thcri]

When your property was surveyed I am sure GPS was not used. They can follow the same formula using new equipment but they have to base it on what was used back when the original was done. Today's GPS are pretty accurate but will onlly be within 20 feet at best. I took some surveying readings for a friends of mine and put them in my GPSmap60CS which is good down to 9 feet but did not come close to his pins. However, if I mark a pin then use my GPS to find another pin I would be right on.

murph

 

[MikePA]

Get the deed to your property, which should be available at the county court house. Every deed I've ever seen begins with the words, "Beginning at a point...." then proceeds to travel around the perimter of the property with a sequence of both directions and distances. It ends with '...containing xxx.xx acres". Surveyors do no use language any more difficult than a high school math class. If you can read a GPS or a compass and measure distances, you're in business. No offense intended, but there's nothing hard to decipher and it's certainly not done so the surveyor gets to come out again. Most homeowner type questions can be answered over the phone for free.

 

[VA_Joe]

There are a couple of methods for getting accurate GPS readings. The first is to use one of the available GPS correction services. These services broadcast GPS corrections taken from a receiver placed at a known (i.e. precisely known - such as a USGS marker) location in your area. The idea is that their readings will have errors similar to what you see at your location. The closer this "known point" is to your location, the better your readings will be (if you really want to be accurate - you could even set up your own GPS correction reference at a known survey marker).

The other way of doing this is to average GPS readings over a long period of time (6 hours or more). The idea here is that the errors, once averaged will cancel each other out. To do this you need a receiver that will provide enough digits on the right side of the decimal point (my elcheapo $89 Garmin eTrek limits the digits such that the best I can do is 5 feet - other receivers will provide more digits) and a computer to collect the data via the serial port (or USB). Using Hyperterminal, create a log file with the GPS output. Import the log file into excel as a comma delimited file. Find the column containing the long and lat and do an average. The average is the answer. As I said - your accuracy is going to be limited by the output of the receiver. Although Garmin uses the same chip set in many of its models, the cheaper ones don't output as many digits as the more expensive ones - go figure.

Anyways - hope this helps you out. Have fun.

Joe

 

[Code54]

WOW - I had no idea that this was so complex... But now I feel I have a clue and am on the right track. On Monday I will have a copy of the Deed so that should help a LOT! The info everyone provided was VERY helpful - thank you! I found all but one pin and think I will find it with a bit more looking. I asked about getting it resurveyed at the time of the purchase but the bank people were happy with the pins and did some checking (not sure how but it is a very small town) and stated they were correct. (Plus I double checked with some neighbors and they were helpful in supplying extra info.) Anyway a survey for my 8 acres is OVER $1800.00 so I think I am going to use the info you all supplied and take some extra time and figure it all out. Thank you all once again!!!

 

[VA_Joe]

There are also a lot of web pages on this topic. Do a few google searches. Just about anything you want to know or do is out there for the reading (even a lot of software that is free for the taking)