How to determine distance in feet between 2 way points?

[Mark Christianson]

I have some waypoints on my GPS that I am trying to figure out how to get the distance in feet between them. Long story as to why I need this, but someone must have a fancy calculator to figger it out.

I need the footage between:

N46 18.858

W95 34.437

N46 18.710

W95 34.495

And the footage between:

N46 18.858

W95 34.437

N46 18.700

W 95 34.513

[LMITOUT]

Which GPS do you have? I want to say that some of the Lowrance units will give you the distance between waypoints. I believe there is a distance tool somewhere in the menus and I think I've used it or something like it before.

[LMITOUT]

I had my H2O sitting here and fired it up. I clicked on Menu and on the drop down list there is a selection for "Find Distance". Select that and the map will reappear. Scroll over to the first waypoint and hit enter. Now scroll to the next waypoint on the map and a trail will be shown behind your cursor. On the bottom of the screen it will show the distance from the starting point to the cursor location.

[Finns]

First numbers seem to be 0.18 miles or 950.4 feet and the second set of numbers seem to be 0.19 miles or 1003.2 feet.

[Mark Christianson]

Thats correct, but there is roughly a 50 ft delta if you calculate .18 miles and .19 miles. What I mean is that you can walk about 50 ft before the GPS will increment a hundredth of a mile.

I am looking for a precise footage between waypoints.

I have an H20c, and I got the same numbers. I need the exact footage though between those waypoints.

[Ralph Wiggum]

Tough to get an exact distance when your waypoints could have a 30' error in them.

[Finns]

Hire a surveyor.

[DinkADunk]

To calculate the distance between two lat/lon points you will need the following;

1) spheroid

2) accurate elevation data for the two points

3) map projection that you want to use to determine the distance. All map projections will distort features, you choose which variable you want distorted (angluar measure, area, etc)

4) define precise

Or you can use the following (Great circle calculation, angles in radians)

Distance = acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos(lon1-lon2))

or assuming a flat earth it's just the Pythagorean theorem;

distance = sqrt(deltaLat**2 + deltaLon**2)

[Mark Christianson]

Surveyor it is I guess.

Just looking for a point to point number thats on flat ground.

I shouldnt say precise is required, but something a bit closer than .18 miles and .19 miles.

Here I thought it might be as easy as some HSOforum that had a spot to plug in some info, and have it spit out the number.

The internet is far less powerful than I hoped.

OK, the long story why I am looking for this.

My Dad bought some land and is building a retirement house.

There is a lake in the area, and by the rules, he cannot build within 1000 ft of the lake without some special permits and additional fees. So he is trying to figure out within reason, where this 1000 ft line would be. If it was a wide open field, then we could use a rangefinder to get the idea, but its all woods, so he asked me to take some shots with the GPS and see if we could use that to figure out where this 1000 ft line would be, and from there he can get some rough ideas on where the house could be positioned.

[DinkADunk]

Get a map of the property from the county assessors office. Read the scale, lay off 1000 feet on a protractor and then follow the shore. That will tell you (roughly) where a 1000 feet inland is. From that you should be able to generate some way points. If your county's tax assessors office has property computerized then they should be able to generate a map with a 1000ft line for you. Contact the county's GIS resource (that would be listed on their web site). This kind of work is a piece of cake with the correct software.

[Finns]

Here I thought it might be as easy as some HSOforum that had a spot to plug in some info, and have it spit out the number.

There is. That's why I gave the distances I did.

[schweady]

I used the gpsvisualizer site for their Great Circle distance, which they say uses "the thoroughly nasty Vincenty Formula, which accounts for the flattened shape of the earth." More geographic calculators and related info there than the common man can handle.

Assuming the accuracy of the waypoints:

a) 932 ft or 0.1765 mi

1,012 ft or 0.1917 mi

[Mark Christianson]

Thats more what I was looking for.

I had the .18 and .19 miles and converted that to feet. But knew that wasnt probably quite as accurate as I needed.

[nine-tiner]

Just make sure that you use the "water line" that the DNR considers golden to measure your offests from. I would suggest a licensed surveyor, one would hate to miss by a couple feet and have to start over on something.

[Mark Christianson]

This is really more to gain a good idea, rather than use this info and start digging. An additional "buffer" will be used to gauge where to put it.

Of course, surveying will be done at some point. Right now its just to determine the potential area for the house and from there start things in motion.

[fishermatt]

Otherwise couldn't you use Google Earth? That has a distance calculator.

[upnorth]

You can try one of these. Not sure if they are going to be much more accurate tho.

Here's one

Another one

[Mark Christianson]

Thanks all. I have what I need.