My Javad Story

nate-the-surveyor · 2016-07-21T23:29:00Z

I started out, asking alot of questions, some 12 or so yrs ago. When I first joined the RTK game. I was already in the L1 GPS game.I wanted answers from USERS, not VENDORS.I asked the Trimble people, and was told "GPS don't work in the woods".I asked the Topcon People, and was told, "We have users who use them in the woods"I asked the Other vendors, and users, and at that time, was told that Topcon was the best unit to use in the woods. (at that time, Topcon was a Javad, painted yellow, and sold by Topcon.) I went, and ran with another surveyor, who had Topcon Gear. He had Hiper GGD. What I learned was that it worked fairly well, but in bad spots, it would occasionally give a bad shot. Especially when the Satellite configuration was poor. Then, I went and talked with another user of Topcon gear, and he told me that for woods work, the Legacy E was the most robust, but the wires were a pain. So, I found a Legacy E unit, from an engineering firm, in Kansas, who was restructuring. They had paid some 42k for it.I took it home. And, with it, I learned many things. Set it in the woods, and there are 2 kinds of errors it makes.1.) Bad Init. This typically results in a shot that is up to 7 or 8 feet off. Rarely more. This is the "big one" The is the one that can bite you.2.) Poor shot. This is one, that is just sloppy. Up to 1/2 foot off. Usually is within 0.3' So, I determined that these are my errors to watch. The way to catch these, is to REPEAT the observation. With a time frame between shots. I sat under a big oak, and shot a point for 3-1/2-4 hrs, in me early days, and watched it accumulate coords, within a 0.7 error ellipse. I had a good survey on it, so I pretty well knew what was the correct coord, but I wanted to learn. I had 2 shots that were around 5' out. What I learned with this, is that the unit will be right more often than it is wrong. And, the worse the environment, the more often it is wrong, and the more time it is going to take, to quality check it.So, I continued experimenting. (nobody was really talking about HOW to do this, so I was sort of on my own) Those who were talking, were brief, just said shoot, it again, and again, over time. I kept at it. I developed a habit of shooting 3 shots, and using the one closest to the middle of the group. If it was in any way critical, it always got 15-30 minutes, so I could OBSERVE the shot spread. I learned to raise and lower the rod. (This works to modify the Multi path environment) If it is in an area with lots of HORIZONTAL branches, ie, oaks, big horizontal, limbs, UP and DOWN changes the environment. If it is in an area with lots of VERTICAL trees, (tree trunks and such) up and down does NOT check it so well. The only way to check these is to MOVE it horizontally. And, compass and tape to the prev shot. If they agree within 0.15' we are probably good. Usually this is done, within 5-8 foot of move. This can save some time. Get 2 shots 8' apart, that agree, and you know it is not "the big one". Must loose init between shots. Must understand and use compass. Think in terms of an inverted tripod. 3 open holes to the sky, and you can get it. It may take a while, but you can do it. Confirmed points is the ONLY way to go, with rtk in harsh environments. This is an absolute, for woods work. Multiple shots, over a period of time. I am FINDING errors in the 3 foot magnitude, by others, using GPS in the woods, without adequate QUALITY CHECKING. I know where these errors come from. Somebody got in a hurry, and did not check their work. Usually 2 points that are supposed to be 60' apart, are found 56.5'. Etc.Well, I am a cheap skate. Don't like to spend my money. Don't have alot of it anyway.But, I knew from experience, that IF it was a JAVAD product, it would be a leader of the pack. I called Shawn Billings, down in TX, and he offered to come and demo for me. I tried to get some other surveyors to come and see, but only one was interested. What I saw, made me smile. Here is what I saw.The Javad LS does several things. It runs with an "Open Squelch". Picks up the faintest signals. In the woods. 1.) It gains a fix, and throws it out. Does this OVER and OVER. Until it develops an statistical "pile of coordinates" to say it has the right group. That is what all the clicking sounds are.Then, it ASSUMES it has the right group. A group is typically a pile of coords, within a radius of 0.15'. It can make up to 10 groups.2.) Then, it tries to narrow it down within this group. So, it will run for some 2 minutes, collecting all fixes, that fall within this radius. Then, it goes back to Phase 1 above, and double checks that a certain percentage of the shots are within this 0.15'. If statistically it determines that it has the right group, then it allows you to store it.Now, you have a shot, that most of the time, (I really push it in the deep dark forest) is within 0.10'If it matters much, you repeat this 3x, and then it uses a weighted average, and makes an average of th...

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GNSS & Geodesy

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shawn-billings

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Kilgore. Let's get together some time.

Posted : July 24, 2016 2:01 pm

nate-the-surveyor

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Let me say this.
ALL measurements contain error.
Go with the best.
This could never be more true, than with RTK GPS. Having Post Processed running simultaneously, is a good thing.
Always buy the best you can.

Posted : July 24, 2016 2:27 pm

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My Javad Story

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