Posted on 07/03/2010 1:07:01 PM PDT by thackney
I have coordinates from a Sabine River Authority survey map created around 1967.
I am trying to get the coordinates to modern GPS coordinates to use in Google Earth or similar programs.
I thought the coordinate system was NAD27 but my longitude is deemed invalid by the conversion programs I have tried.
I have spent a couple hours searching via the internet. I thought at this point I would turn to our FReeper knowledge bank.
The Latitude is listed as: N.88°54'23.4"W. The Longitude is listed as: N.00°21'52.7"E.
The letter designation do not make sense to me, but with the multidude of other points shown, I know they are not a simple typo.
I know from Google Earth this point is approximately: Lat: 31.44794° Lon: -93.63124°
I have several points along a conveluted path that I would like to plot using GPS.
If someone could point me to a conversion equation or web site, I would appreciate the help.
Thanks! thackney
But I don't know enough about the topic to understand how to use what it is describing.
Your map should have the correct coordinates system that was used for the map printed on it. Do you have the book for the GPS, that can help.
I don't think CORPSCON does WGS84 directly, but you can use it for approximation or a step in-between.
Or could be polar-type intersections. I’m guessing they are specific to the Authority.
These values are not lat and long. These are bearings used by surveyors.
N.88°54'23.4"W means start an N., then rotate W. (counterclockwise) 88°54'23.4".
N.00°21'52.7"E means start an N., then rotate E. (clockwise) 00°21'52.7".
Surveyors use these types of bearings instead of 360 degrees. All bearings are <= 90 degrees. They allow easy conversion of reverse bearings because they are the same number. For example, N45W is the reverse bearing of S45E.
oops, “start an” should be “start at”
Great explanation. I am not a surveyor so, at first, I was thinking that spot is up near the North Pole!
A clear, no frills answer. Thanks.
You can get GPS coordinates from google maps, but this might be easier.
http://itouchmap.com/latlong.html
Now that he knows those are bearings he needs to know the start point and the length of each bearing, right?
One of those numbers should be Latitude, and one should be Longitude. There should only be ONE letter in each. N/S in Latitude, E/W in Longitude. Try that second number with a W in front of it instead of an N, and drop the W from the end of the first number. Those may be why you’re having trouble.
Thank you, that makes sense.
The two values were Northern and Eastern boundaries of a property. I was trying to use the combination to specify a point to GPS, but I see that isn’t the case.
I also have some Nearby X,Y coordinates from whatever system was used as a reference. I will have to figure out what they represent to learn more.
I’ve been going through that site for a while, but not having enough information to make it work.
I now understand (see above post) that I was intersecting two bearings, they were not a coordinate system.
I have another nearby coordinates of
X=1,644,780.863
Y=287,385.764
I will have to learn what that references. I now understand I have bearings and distances to get from that starting point, to the points I’m trying to define. I will just have to do some more research.
Sadly, the land office with this data is about 4 hours one way from my home. Another friday off work to look forward to driving.
Thanks for the help.
That's basically correct, but it's not as straightforward as it sounds. I started to write and explanation, but it's very involved. He might want to consult a surveyor or someone familiar with surveying principles.
My problem is the starting point.
The ultimate goal is to turn the multitude of points I have into GPS coordinates to reasonably locate on both Google Earth as well as physically with a GPS.
I am negotiating a land trade. Ultimately we will use a surveyor when we reach an agreement. While we are in the negotiating phase I'm trying to consider some possibilities while calculating some acreage options of very convoluted pieces.
To identify the coordinate system, look for something on the map labelled "Meridian." If there is a legal description, it might name the meridian. In legal descriptions, meridians are sometimes abbreviated, such as "W.M." for Willamette Meridian (covering OR and WA). If the land is in Louisiana, there's a good chance your map uses the Louisiana Meridian. If you can identify the meridian, you should be able to convert your X,Y coordinates to GPS coordinates.
It is west of the Mississippi River so it would be the Louisiana Meridian.
I have a set of X,Y coordinates nearby on my map. Where do I go to find the GPS of that coordinate?
From there I can follow the distances and bearings to get where I need to be.
Is the Meridian coordinates given in feet?
As long as I now the initial point of the system, can I use the coordinates as measurement in feet to the location?
http://en.wikipedia.org/wiki/Public_Land_Survey_System
Find a program or website that converts Louisiana Meridian coordinates to GPS coordinates. Another avenue to explore is the county website. Some county websites have extensive mapping capabilities that meet or exceed Google Earth standards.
From there I can follow the distances and bearings to get where I need to be.
You might need to rotate bearings on the map first. Bearings on the map may not agree with bearings in the coordinate system. First, I would do a check between two X,Y coordinates. Ideally, find a line on the map that has two X,Y coordinates on it. Start with one X,Y coordinate and assume the second is unknown. Calculate the second X,Y coordinate using the bearing and length on the line. If your result matches the second X,Y coordinate value on the map, the rotations agree. If not, you'll have to rotate the bearings on the map.
I understand. Thanks for the help.
Ultimately I’ll be back in the same office I made the copies from yesterday. But I suspect I won’t be able to get back until August.
If I find a conversion system, I’ll get to play with it until then.
Your explanation that I was using bearings and not coordinates made a lot of my map suddenly make sense.
In hindsight, it was rather foolish to expect that property lines exactly lined up with North-South and East-West directions.
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