Well, yesterday my wife and I finally took the plunge and signed the deed for a hundred acres of farmland in rural Virginia. I haven't told her yet, but I signed her over as collateral (kidding). Seriously, though, this has been a very big decision and when I allow myself to think about it it is quite exciting. However, coming from a rural Midwestern background, where the legacy of Calvinism is alive and well, it is a rare moment that I allow myself the luxury of enjoying it. I'm mainly focusing on what we need to do to get the bison fencing installed.
First, among those things I need to do is identify the property boundaries. Where I grew up, in Wisconsin, finding property boundaries is fairly easy because most property boundaries follow a square grid pattern. In the eastern US, though, it a very different story. Many property boundaries are fractured and jagged. Sometimes this is because the boundaries follow a meandering stream, but often there appears to be no logic behind it. For instance, our property is one hundred acres and has close to fifty individual marking points on it. Some of these references are metal spikes or concrete markers, while others are specific species of trees, such as S. Gum and R. Oak (Sweet Gum and Red Oak respectively).
Finding the exact boundary may be a bit challenging, but I've taken a few steps that I hope will help me. The first thing I did was to buy a metal detector. Assuming there wasn't a major Civil War battle fought on the property, a metal detector should help me located the metal stakes that had been used to mark some of the boundaries. In addition to the metal detector, I've also managed to review each of the markers listed on the plat and convert their survey annotations into precise coordinates which have been entered into my GPS device.
To transfer the survey information into something I could put in my GPS, I first had to figure out how to translate a plat into a compatible coordinate system. In my professional life, I've had ample exposure a variety of maps and mapping technologies, but I have not previously had to interact directly with data from a property boundary survey. Though different from many other types of mapping data, the methodology is sound. The first thing one must pay attention to on a plat is the method of orientation. In the plats I used, magnetic north (magnetic declination) was used for orientation. For plats, knowing the year it was made is critical because the magnetic declination changes over time. On some of the plats, the actual magnetic north measurement was noted, while on others only the year was listed. Fortunately, in those instances, I was able to find an awesome website created by the National Oceanic and Atmospheric Agency, which will tell you the magnetic declination for a given location at a given time.
Aside from the magnetic declination, the other important part of the plat is the boundary marker or markers. This is a semi-permanent object or objects that serve as a reference point from which the rest of the boundary can be calculated and measured. On one of my plats the reference point was the center of an intersection of roads (remember this is a very rural area). From this starting point a line is drawn on the plat traveling a specific distance along a very precise bearing. Where the prescribed length has been reached is the location of the next point, which serves as the reference point for the next line. The process repeats itself until the surveyor ends up back at the original marker. The plats (at least in Virginia) express the bearing measurements as degree, minutes, and, sometimes, seconds either east or west of either north or south. That is, the plat might describe a marker as being 10 degrees and 45 minutes east of south or 50 degrees and 10 minutes east of north. If this kind of thing is new to you, you may find it difficult, but it is actually simpler than it seems. The complexity comes from the fact that you are given four ways in which to describe the same thing. Anyway, the second part of the line description in a plate is the distance. This is just a straight forward measure of the distance between the two markers in feet.
As a non-surveyor, I found myself struggling to keep all of the measurements straight, so I wrote a small series of python functions that converted everything into straight azimuth. The functions I used are as follows:
def A(degrees,minutes,NS,EW,magnorthdeg,magnorthmin,magnorthEW):
if NS == "N":
if EW == "E":
azimuth = EofN(degrees,minutes)
else:
azimuth = WofN(degrees,minutes)
else:
if EW == "E":
azimuth = EofS(degrees,minutes)
else:
azimuth = WofS(degrees,minutes)
magdeg = min2deg(magnorthdeg,magnorthmin)
if magnorthEW == "E":
magdif = magdeg
else:
magdif = magdeg*(-1)
az = azimuth+magdif
return az
def EofN(degrees,minutes):
deg = min2deg(degrees,minutes)
a = deg
return a
def WofN(degrees,minutes):
deg = min2deg(degrees,minutes)
a = 360-deg
return a
def EofS(degrees,minutes):
deg = min2deg(degrees,minutes)
a = 180-deg
return a
def WofS(degrees,minutes):
deg = min2deg(degrees,minutes)
a = deg+180
return a
def min2deg(degrees,minutes):
mins = float(minutes)/60
deg = float(degrees) + mins
return deg
In the original script magnorthdeg, magnorthmin, and magnorthEW were defined inside the first function, so all I really needed to do was start with:
import Surveys as Su
Then for some thing like "9 degrees and 10 minutes east of north" I would just type:
Su.A(9,10,'N','E')
which returned: 3.416 (the azimuth from true north)
The nice thing about these functions is that they take into account the difference between magnetic north and true north and also convert degrees and minutes to decimal degrees. This makes it much easer to then generate a point in a modern Geographic Information System (GIS). By the way, it is pronounced "G-I-S," not "JIS." For this project, I decided to use the free software program Quantum GIS to record each bearing and distance and calculate the coordinates of each survey marker. Particularly useful for this task was a tool I found in the QGIS python plugin repository call "Geometry from Azimuth and Distance," which enabled me to digitally generate the entire boundary and find the coordinates of each marker in less than a day. Just to be on the safe side, I've generated coordinates for both WGS84 and NAD83 UTM17N. I know it probably doesn't matter on this scale, but I'm a little anal about these things.
Once I had the two types of coordinates for each point I exported the date as a spreadsheet, printed two copies and then entered the points into my GPS device. My hope is that with the combination of the metal detector and the GPS I should be able to locate and mark the boundary and begin planning the fence installation. We're heading out there tomorrow.
First, among those things I need to do is identify the property boundaries. Where I grew up, in Wisconsin, finding property boundaries is fairly easy because most property boundaries follow a square grid pattern. In the eastern US, though, it a very different story. Many property boundaries are fractured and jagged. Sometimes this is because the boundaries follow a meandering stream, but often there appears to be no logic behind it. For instance, our property is one hundred acres and has close to fifty individual marking points on it. Some of these references are metal spikes or concrete markers, while others are specific species of trees, such as S. Gum and R. Oak (Sweet Gum and Red Oak respectively).
Finding the exact boundary may be a bit challenging, but I've taken a few steps that I hope will help me. The first thing I did was to buy a metal detector. Assuming there wasn't a major Civil War battle fought on the property, a metal detector should help me located the metal stakes that had been used to mark some of the boundaries. In addition to the metal detector, I've also managed to review each of the markers listed on the plat and convert their survey annotations into precise coordinates which have been entered into my GPS device.
To transfer the survey information into something I could put in my GPS, I first had to figure out how to translate a plat into a compatible coordinate system. In my professional life, I've had ample exposure a variety of maps and mapping technologies, but I have not previously had to interact directly with data from a property boundary survey. Though different from many other types of mapping data, the methodology is sound. The first thing one must pay attention to on a plat is the method of orientation. In the plats I used, magnetic north (magnetic declination) was used for orientation. For plats, knowing the year it was made is critical because the magnetic declination changes over time. On some of the plats, the actual magnetic north measurement was noted, while on others only the year was listed. Fortunately, in those instances, I was able to find an awesome website created by the National Oceanic and Atmospheric Agency, which will tell you the magnetic declination for a given location at a given time.
Aside from the magnetic declination, the other important part of the plat is the boundary marker or markers. This is a semi-permanent object or objects that serve as a reference point from which the rest of the boundary can be calculated and measured. On one of my plats the reference point was the center of an intersection of roads (remember this is a very rural area). From this starting point a line is drawn on the plat traveling a specific distance along a very precise bearing. Where the prescribed length has been reached is the location of the next point, which serves as the reference point for the next line. The process repeats itself until the surveyor ends up back at the original marker. The plats (at least in Virginia) express the bearing measurements as degree, minutes, and, sometimes, seconds either east or west of either north or south. That is, the plat might describe a marker as being 10 degrees and 45 minutes east of south or 50 degrees and 10 minutes east of north. If this kind of thing is new to you, you may find it difficult, but it is actually simpler than it seems. The complexity comes from the fact that you are given four ways in which to describe the same thing. Anyway, the second part of the line description in a plate is the distance. This is just a straight forward measure of the distance between the two markers in feet.
As a non-surveyor, I found myself struggling to keep all of the measurements straight, so I wrote a small series of python functions that converted everything into straight azimuth. The functions I used are as follows:
def A(degrees,minutes,NS,EW,magnorthdeg,magnorthmin,magnorthEW):
if NS == "N":
if EW == "E":
azimuth = EofN(degrees,minutes)
else:
azimuth = WofN(degrees,minutes)
else:
if EW == "E":
azimuth = EofS(degrees,minutes)
else:
azimuth = WofS(degrees,minutes)
magdeg = min2deg(magnorthdeg,magnorthmin)
if magnorthEW == "E":
magdif = magdeg
else:
magdif = magdeg*(-1)
az = azimuth+magdif
return az
def EofN(degrees,minutes):
deg = min2deg(degrees,minutes)
a = deg
return a
def WofN(degrees,minutes):
deg = min2deg(degrees,minutes)
a = 360-deg
return a
def EofS(degrees,minutes):
deg = min2deg(degrees,minutes)
a = 180-deg
return a
def WofS(degrees,minutes):
deg = min2deg(degrees,minutes)
a = deg+180
return a
def min2deg(degrees,minutes):
mins = float(minutes)/60
deg = float(degrees) + mins
return deg
In the original script magnorthdeg, magnorthmin, and magnorthEW were defined inside the first function, so all I really needed to do was start with:
import Surveys as Su
Then for some thing like "9 degrees and 10 minutes east of north" I would just type:
Su.A(9,10,'N','E')
which returned: 3.416 (the azimuth from true north)
The nice thing about these functions is that they take into account the difference between magnetic north and true north and also convert degrees and minutes to decimal degrees. This makes it much easer to then generate a point in a modern Geographic Information System (GIS). By the way, it is pronounced "G-I-S," not "JIS." For this project, I decided to use the free software program Quantum GIS to record each bearing and distance and calculate the coordinates of each survey marker. Particularly useful for this task was a tool I found in the QGIS python plugin repository call "Geometry from Azimuth and Distance," which enabled me to digitally generate the entire boundary and find the coordinates of each marker in less than a day. Just to be on the safe side, I've generated coordinates for both WGS84 and NAD83 UTM17N. I know it probably doesn't matter on this scale, but I'm a little anal about these things.
Once I had the two types of coordinates for each point I exported the date as a spreadsheet, printed two copies and then entered the points into my GPS device. My hope is that with the combination of the metal detector and the GPS I should be able to locate and mark the boundary and begin planning the fence installation. We're heading out there tomorrow.