Sizing GPS Data

[heedaf]

I got GPS data from my lot I want to build on.  Is there a way to scale it?  Lot is 100' wide but the gps coordinates come in at 157' wide.  Not sure why but all I need is the slope of the lot.

[Rich_Winsor]

100/157 = 0.6369426751592357

Multiply your gps coordinates by this number and they will be 100' wide. 

[SHCanada2]

If you have multiple points You probably want to take a subset that fit within 100ft.  You could scale the elevation data if you are only given two points for 157ft. What exactly do you have?

 

A question would be, did you get wrong GPS data for 100ft or did you get bigger GPS data that represents 157ft. And did you get more than 4 points

[heedaf]

1 hour ago, SHCanada2 said:

If you have multiple points You probably want to take a subset that fit within 100ft.  You could scale the elevation data if you are only given two points for 157ft. What exactly do you have?

 

A question would be, did you get wrong GPS data for 100ft or did you get bigger GPS data that represents 157ft. And did you get more than 4 points

Just got a gps app on the phone and walked the lot.  Strange that it would be that far off.  Around 400 points with the lot.  I guess I need to go measure the lot to make sure it is 100' wide.

 

[heedaf]

7 hours ago, Rich_Winsor said:

100/157 = 0.6369426751592357

Multiply your gps coordinates by this number and they will be 100' wide. 

Is there a way to do this via software or do I need to manually do it?

[JiAngelo]

Pretty sure this isn't a scale problem.  Phone gps apps are only accurate to +/-16ft radius.  That's +/-16ft at each point you measure. The error distance grows if obstructions exist - trees, clouds, adjacent structures.  The quality of the phone's internals affect this as well.

 

If you stood on two points that you know are 100' apart and shot 157',  find a third point that is a known set distance from the first two points. 

Best if 【1-3】does not equal 【2-3】 . Go out there with a 100ft tape and pick one.

 

Calculate (Actual Distance) / (Recorded distance) values for points【1-2】, 【1-3】 and 【2-3】, if they dont all equal 100/157 then you can't scale.  I would wager if you shot 【1-2】 again you'd get a different number.

[SHCanada2]

2 hours ago, heedaf said:

Just got a gps app on the phone and walked the lot.  Strange that it would be that far off.  Around 400 points with the lot.  I guess I need to go measure the lot to make sure it is 100' wide.

GPS do not give accurate elevation data(which is needed for slope), like not even close, I think mine might be accurate to 50ft vertically(absolute) and who knows on a delta between two points. I tried it a few years back and it was all over the place for the delta. Your better bet is a transit or laser at dusk ....once you determine where the property corners are at physically.

 

or go old schoold with a water level

 

I also have a zip level for when you do not have line of sight.

 

..or just ask the customer for a survey...or get one done.

 

The cheapest way, laser level if you know where the property corners are

 

Edited 22 hours ago by SHCanada2