I’ve got the SparkFun GPS-RTK-SMA Kit and using an NTRIP data correction source from the Iowa DOT. Located in Northern Iowa.
I’ve created a custom application to generate GNSS points into a CSV file and load into SW_MAPS. I have generated these points to be certain distances from each other. When I load them into SW_MAPS, use that to pin the points in the ground, and pull a tape – the measurements are exactly what I intended them to be.
When I use the measure tool in SW_MAPS there are slight differences. For example a 345’ line (generally SW to NE) on the ground shows 344.125’ in SW_MAPS. A 210’ line (generally NW to SE) on the ground shows 210.180’ in SW_MAPS.
I tried modifying the coordinate systems in SW_MAPS and the measurements are not affected regardless of what CRS is used in the application.
Lots to unpack here. When gps surveying you’re on grid distances which have to be converted to ground distances. Think of it as the earth is a piece of paper and we’re trying to flatten it although we know the earth is a complex shape. This is called scale factor. Certain places have more scale factor than others.
SW maps is great for general use but not what I use when I am surveying with my GNSS stuff.
There’s also inherit error with rtk. Good RTK setups I can check with a total station 0.02’ however I am using a low distortion projection not straight state plane. Also you need to make sure you’re using the same datum and reference frame as the correction network.
I guess this is kind of independent of the receiver and more of an app/datum issue.
The coordinates were generated using a custom self-built Python script (geopy library).
When I load them into SW Maps it takes me right to them (whether or not they’re location is accurate on the ground is unknown, but they are relative to each other), when I measure distances between them they are exactly what I programmed them to be. But loading into SW Maps the measure tool is off by, not a lot, but significant enough.
My RTK correction data is coming down as NAD83(2011)(Epoch 2010.000 so I can see where that might cause an issue in the field but finding the coordinates and measuring them manually they are dead on. So it’s like SW Maps is not translating them to measurements correctly.
In any case I’m using this to lay out and paint soccer fields instead of dragging around tape measures like I’ve done the past 3 years. Centimeter accuracy is not necessary but the more accurate in plotting my points the better for my sanity.
I guess my method is fine as laying out the field the measurements are perfect, would just be nice if SW Maps also reflected the proper measurements.
Here is my points file if you guys have any other ideas.. totally new at this so slowly learning how it all works.
Good question.. I have my design points (from python script) which I load into SW Maps. I took those to the field and marked the 4 outside corners of my soccer field as they appeared in SW Maps using the Stake Out tool in the app, which worked well.
I pulled tapes and validated that the staked points matched what the distances should be according to my design points. What is not matching is that when I use the measure too in SW Maps showing 10 inches short in some instances and a couple inches long in other instances.
I would think that if my design points were pinned in the field, measured, and the measurements match my expectation of that what they should be, the software would also show it closer than it does.
It’s possible that my points are not in the field where they were intended to be in my design (not my focus right now, and not super important to the task), but relative to each other they are right on.