{"id":1,"date":"2023-12-30T12:00:53","date_gmt":"2023-12-30T12:00:53","guid":{"rendered":"https:\/\/bendauphinee.com\/writing\/?p=1"},"modified":"2024-12-20T15:06:44","modified_gmt":"2024-12-20T15:06:44","slug":"to-know-where-you-are","status":"publish","type":"post","link":"https:\/\/bendauphinee.com\/writing\/2023\/12\/30\/to-know-where-you-are\/","title":{"rendered":"To Know Where You Are; High Precision Mapping From Scratch"},"content":{"rendered":"\n

20 min reading time; ~4300 words<\/p>\n\n\n\n

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The fun of owning rural property is that knowing where your land actually starts and ends is a guess usually. Sure, you have a parcel description, and maybe even an online service with “official” GIS boundaries (for us here in New Brunswick, this is GeoNB<\/a>). However, since it’s in the middle of the forest, the odds of you having an actual surveyed and monumented boundary line are very low. Which also means the odds of the online boundaries being correct isn’t great either. This post is a dump of all the experiences I’ve had over the past 3 months, on my quest for accurate mapping.<\/p>\n\n\n\n

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I purchased a lot like this recently, and since I want to build an event space on it, knowing where it actually is became very important. My first pass at figuring this out was to install Map Plus<\/a> on my iPhone 14 Pro, and then create shapes for my and my neighbors lots from corner coordinates copied from GeoNB. This iPhone has a dual frequency GPS (L1 + L5<\/a>), which should get me to roughly 30 cm (11.8″) accuracy. In real-world testing, I’ve gotten at best 3.5 m (11.5′) accuracy, but mostly 4.5 m (14.75′), which is good enough to eyeball things, but not enough certainty to be confident that something is where you think it is.<\/p>\n\n\n\n

Using this combination, I was able to start feeling out my boundaries, and open a dialog with my neighbor about the fact that he wasn’t in fact in the middle of his property with his camper, but more likely at or over the edge (which he was not happy about, since he wanted to be in the middle). I had been planning to get a survey of that side of my property anyway, because I wanted to know for sure where it was, but this starter tool was great for at least opening the conversation while I waited for my surveyor to get back to me.<\/p>\n\n\n\n

Map Plus<\/h2>\n\n\n\n
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Once I had installed this app on my phone, and got some basic boundary shapes plugged into it, I spent a few weekends wandering over my land, to get a feel for what I had purchased. Map Plus proved to be very useful for my initial survey, and I’ve purchased about half of the functionality they sell with it. <\/p>\n\n\n\n

The screenshot to the right shows the results of the data I collected (close to 400 data points). Of all the tools I’ve worked with so far, this one is the easiest in terms of usability. While obviously aimed more at the casual market (with no ability to use external GPS sources), it still has a lot of useful functionality, such as the ability to handle shapefiles and other GIS formats. In that image, you can see the results of some of the work I did, where I collected data in the app, exported it, generated a shapefile (via QGIS<\/a>), and imported it back in as a cleaner map element.<\/p>\n\n\n\n

If you aren’t looking for that higher accuracy GPS, Map Plus is a great app. The ability to even do things like upload \/ download data via a built in web server is by far the smoothest workflow I’ve found to get data in and out. Honestly, if this app supported Bluetooth GPS and NTRIP, I’d still be using it as my only app.<\/p>\n<\/div>\n\n\n\n

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While I waited for my survey, I continued to research and learn things. And, of course, get out to my land every chance I could to walk it. Fall, with the leaves out, then not, has been a very interesting time. I’ve spotted some small frogs, a rabbit, and a few birds (including one that burst from it’s hiding spot very close to me and almost gave me a heart attack \ud83d\ude02). As you can see in one of these photos, I’m wearing the delightful “don’t hunt me, I’m a person” blaze orange hat and vest that you need when you’re wandering though the woods during hunting season.<\/p>\n\n\n\n

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An Official Survey<\/h2>\n\n\n\n
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Finally, my survey arrived. On a snowy Tuesday, I drove to the bottom of the mountain, hiked in 3 km (1.9 mi) to my land, and met the surveyor crew. (Normally, I would have driven straight up, but a sedan on a mostly unplowed road, with 10 cm (3.9″) of snow, and no snow tires on yet is a recipe for needing to call a tow truck.) Over the course of the next three hours, myself and the surveyor hacked through the snowy trees, blazing and marking the official survey boundary. At the end of that process, sweaty and somehow also cold, I finally had two official pins and a single line in the woods, that definitively said “this is in fact my land”.<\/p>\n\n\n\n

Given the cost of that line (roughly $4600), I opted to only have the boundary between me and my neighbor defined. The land to my east and behind is all owned by an excavation company, but they’re only operating in the far south west corner of it, so there’s no need yet to have the rest of my boundaries marked, now that I have one official line to pin everything to.<\/p>\n\n\n\n

Once I got the official boundary coordinates from my surveyor, I created a new line in QGIS, and rotated and aligned my and my neighbor’s lot shapes to the new boundary. Turns out, the survey was off a lot more than any of us expected, and moved everyone a hefty 39 m (127′) east, and 8.5 m (28′) back from the road, approximately.<\/p>\n<\/div>\n\n\n\n

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But More Accuracy Though<\/h2>\n\n\n\n

So, coming back to my own survey work now that I had my official border, I finally have something to anchor everything else to. While the initial work I did was great for getting the lay of the land generally, it wasn’t up to the standards I wanted. Going back to some of the same survey points, relying on the phone, I could see very obvious drifting (which makes sense with 4.5 m (14.75′) accuracy). This, of course, is not good enough.<\/p>\n\n\n\n

So, what is one to do when you want an accurate survey, but don’t need it to be certified? Why, get your own survey equipment of course! For about a decade and a half, I’ve been interested in GIS technology. From contributing to OpenStreetMap occasionally to wondering if I could afford to buy a survey grade GPS through to trying to boot up my own OpenStreetMap based server, it’s always been a technology I’ve come back to. After some research, I discovered I needed two GPS receivers to be able to do RTK<\/a>, and get the precision I was chasing. So, let’s go shopping for gear! <\/p>\n\n\n\n

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… On second thought, maybe I won’t.<\/p>\n\n\n\n

After digging around for a while, and looking outside the professional market, I was lucky enough to find the help that SparkFun put together<\/a> for exactly this purpose. Thanks to them, I was able to purchase everything I needed to get centimeter accuracy survey results, with a total spend of less than $2000, and build my base station in a box!<\/p>\n\n\n\n

Achieving Centimeter Accuracy<\/h2>\n\n\n\n

Ok, so, to get to centimeter accuracy, you need two things:<\/p>\n\n\n\n