Coordinate Geometry and Plats

[Samsagaz Gamyi]

Hi, everyone. One question:

 

I have a Garmin Dakota 10. I would like to use it to walk along the borders of my land on all sides.

 

After much searching, I learned that the coordinates on my plat are not absolute, but rather relative to one another. They describe how long a line on the border is at so many degrees from each corner.

 

Tonight, I went to the most obvious corner of my property, recorded it with the GPS, and found that the location showed up correctly in Google Earth.

 

My question: If I only have the absolute coordinates for one corner of my property, is there a program that uses coordinate geometry to help me determine the absolute coordinates of all other corners on the border?

 

Thank you very much.

 

~Samsagaz

[+dfx]

If I understand you correctly, you'll need at least one set of absolute coordinates (which you have) and possibly one set of directional reference, assuming the degrees you have are not relative to true north in some particular datum. If you don't have a directional reference, you can take a second set of coordinates at some other known point, and use the bearing between those two points.

 

Once you have that figured out, you can convert the coordinates to UTM, which will give you regular cartesian coordinates (x/y) to work with. You can apply regular cartesian geometry on those. Whatever UTM coordinates you get as result, you can convert back to lat/long for GPS use. Or just set your GPS device to UTM and just work with UTM coordinates directly.

[Samsagaz Gamyi]

Thank you so much!! This is excellent advice.

 

The extent of my geometry knowledge comes from the Graduate Record Examination study guide.

Is there a particular program which you recommend for the Cartesian geometry operations?

[+dfx]

I'll let someone else answer that

Cartesian geometry is the "regular one" that you know, 90 degrees make a right angle, Pythagorean theorem, law of sines, trigonometry, vector algebra and all that. Not a big deal to do if you're educated in it. I don't know any particular software that will do all that for you though, but I'm sure there's plenty around, and someone else will know some.

[Samsagaz Gamyi]

I appreciate it very much, DFX! You are so kind.

I will do some Google searching in the meantime.

[John E Cache]

Can't you just mark the first point and then walk away from the point so the bearing (+180 or -180) and distance to the point match the plot? If so, mark and repeat.

[+Woodstramp]

"Tonight, I went to the most obvious corner of my property, recorded it with the GPS, and found that the location showed up correctly in Google Earth."

 

If Google Earth and your first coord were jiving, then why not use GE to determine the other corners? Not real familiar with getting coords from GE, but I hear it can be done.

 

You might also check online for a local, or county, or state GIS site. Luckily, we have one for my county in Alabama. The site showed prop boundaries, but if you moved the cursor on the screen it gave weird, regional (East Alabama) XY coordinates. I was able to churn these into Delorme Topo and get "normal" coordinates for the GPS.

[+JBnW]

"Tonight, I went to the most obvious corner of my property, recorded it with the GPS, and found that the location showed up correctly in Google Earth."

 

If Google Earth and your first coord were jiving, then why not use GE to determine the other corners? Not real familiar with getting coords from GE, but I hear it can be done.

 

You might also check online for a local, or county, or state GIS site. Luckily, we have one for my county in Alabama. The site showed prop boundaries, but if you moved the cursor on the screen it gave weird, regional (East Alabama) XY coordinates. I was able to churn these into Delorme Topo and get "normal" coordinates for the GPS.

Doesn't GE display the coordinates of the cursor's location? That is, just hover the cursor over what you believe to be "the spot", and the coordinates are displayed at the bottom of the screen.

[+Woodstramp]

Fish Whisperer (killer screen name, BTW)

 

I don't use GE enough to get real familiar with it. My Dell is old and slow and GE gives it convulsions.

[Samsagaz Gamyi]

@John: Thank you! Good plan. We tried that today but found that the path was riddled with vines and fallen trees, so it will take some time to clear those away. However, we managed to cut and haul a lot today.

 

@Woodstramp: That's a great idea. If I find anything in the Google Maps API, I will share it here.

As for the county GIS site, I checked out mine and found lots of useful information. However, the current version of the site does not show XY coordinates. This may be where JBnW's suggestions come into play.

 

@JBnW: I think I will try that since at least my county GIS/Tax Assessor's website does have aerial photos along with the borders of land parcels, which I will then compare with Google Earth's imagery.

 

You three and DFX are the best! Thank you! I hope this topic helps lots of other people researching this problem.