Camera offset survey
- Thread starter Michael
- Start date
In JFIELD, you can also turn on the camera and measure angles.
The CoGo Direct function can be used to calculate and store an offset point by using the internal compass and camera to determine an offset bearing.
Then determine the offset distance to the desired object with a tape measure or laser distance meter.
The accuracy of 'this azimuth offset method' dependent on the 'magnetic-compass', the 'magnetic declination' (for the position measurement on the earth) to obtain a heading (typically +/- 2 degrees). Then there is the addition of True-North to survey grid 'convergence' . . .
To determine a much more accurate position from offsets, use the CoGo 'distance-distance' Intersection function in the Project Coordinate System (in use) .
The CoGo Direct function can be used to calculate and store an offset point by using the internal compass and camera to determine an offset bearing.
Then determine the offset distance to the desired object with a tape measure or laser distance meter.
The accuracy of 'this azimuth offset method' dependent on the 'magnetic-compass', the 'magnetic declination' (for the position measurement on the earth) to obtain a heading (typically +/- 2 degrees). Then there is the addition of True-North to survey grid 'convergence' . . .
To determine a much more accurate position from offsets, use the CoGo 'distance-distance' Intersection function in the Project Coordinate System (in use) .
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Dragonsnake
New Member
I agree with John Rosco, from personal experience using the javad compass offset, it is better to use a distance / distance intersection technique to locate something that you can't otherwise get a direct shot on. Carrying a handheld laser distance shooter is a good idea when doing distance / distance measurements since it is very fast and accurate.
The drawback is that you need to get 2 separate shots and they need to be roughly 90 degrees apart from each other for best results. But it works great for building corners, etc.
The drawback is that you need to get 2 separate shots and they need to be roughly 90 degrees apart from each other for best results. But it works great for building corners, etc.
DUANE WETMORE
Member
Several years ago I made a pivoting clamp-on pole mount for my Leica laser. That unit can be set for an offset distance from the "0" index at the back of the unit. That way it measures exact distance from the center of the pole since the pivot was made opposite the pole center. Photo attached. Works well for dist.-dist. intersections, just keep in mind if you DPOS later to recalc the point using the measured distances.
Dragonsnake
New Member
Wow!!! That's pretty clever, you must be shooting a lot of building corners lol. I never knew Leica made a handheld like that. How visible is the laser dot? Pretty beefy and easy to find? I've used some units where it's hard to see after about 25 feet or so. Although, I've seen other units in which they have an eye hole you can look through and target manually without the laser, if for some reason the laser is not able to be seen on the surface material you are trying to shoot.
DUANE WETMORE
Member
That old Leica D8 has a 4x camera with a target aiming "box" to use for longer distance or light conditions when the red dot is not visible.
Dragonsnake
New Member
Cool, very cool. That's a big problem with using laser shots in the sunlight is that a surface illuminated with bright sunlight makes it very hard to see the red dot, a secondary aiming apparatus is very much required in the daytime lol.
Yes, two 'offset measurements' are required, but with JAVAD TLS and RTPK, the time to collect (after setting your offset distance) is only a matter of a minute or so, yes ?
Dragonsnake
New Member
Sure if you are out in the open, you can get a signals variety shot in only 5 seconds or so. That means 2 of them would only take 10 seconds of actual time for the gps to determine it's position over 2 separate spots.
It might take a full minute or more if you are in shrouded woods with overhead canopy, which will interfere with the gps signals coming from space. The speed of light is so fast, that even 1 nanosecond of timing error is equal to 1 foot of distance error. That's why sometimes a nanosecond is also called a "Light Foot".
It is also a good idea to put in your point description the compass reading for where the 2 circles will intersect, so you know which one to hold. Because when you do a distance, distance intersection in autocad, the circles will intersect twice, and you want to make sure to pick the correct one otherwise the created point will be very wrong lol.
I've used this technique a few times on pesky boundary corner monuments that are literally set in the middle of the base of a grown tree, and you can't get the gps receiver up on it naturally, not plumb at least.
If you use the tilt compensation with the Javad system, I believe it uses the internal compass for providing the corrections, it does not have a full and true Inertial Measurement Unit (IMU), unfortunately. So that's another reason why you would want to use the distance, distance intersection option.
Although, the horizontal distance, distance technique doesn't work for vertical, bummer.
It might take a full minute or more if you are in shrouded woods with overhead canopy, which will interfere with the gps signals coming from space. The speed of light is so fast, that even 1 nanosecond of timing error is equal to 1 foot of distance error. That's why sometimes a nanosecond is also called a "Light Foot".
It is also a good idea to put in your point description the compass reading for where the 2 circles will intersect, so you know which one to hold. Because when you do a distance, distance intersection in autocad, the circles will intersect twice, and you want to make sure to pick the correct one otherwise the created point will be very wrong lol.
I've used this technique a few times on pesky boundary corner monuments that are literally set in the middle of the base of a grown tree, and you can't get the gps receiver up on it naturally, not plumb at least.
If you use the tilt compensation with the Javad system, I believe it uses the internal compass for providing the corrections, it does not have a full and true Inertial Measurement Unit (IMU), unfortunately. So that's another reason why you would want to use the distance, distance intersection option.
Although, the horizontal distance, distance technique doesn't work for vertical, bummer.
May we suggest reviewing the JAVAD Workshop video "Recon to Report" and the time ~21:00 into the video about Gathering Survey Points
In the video, collecting a CoGo Distance-to-Distance' offset measurement from 'a tree center' is outlined.
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Dragonsnake
New Member
Sure I'll take a look
Dragonsnake
New Member
Always good to see Shawn Billings! I saw a lot of his videos when I first got the Javad system back in 2022. Although I hear he doesn't work for Javad anymore. He makes a good point in that video, if you use a resection technique with 3 shots then you don't have to worry about which of the two intersections to hold in a distance, distance 2 shot technique.
I wonder what he thinks of the new pre-release version of J-Field...
I wonder what he thinks of the new pre-release version of J-Field...