Rookie questions on total station setup. Geodimeter 4400/ATS

I don't have a 4400 but it sounds similar to 600 series. These also use RMT if they are autolock capable, so possible answers are:

1. If you are close to the instrument you have to move slow because it can't keep up. The further away the better it gets.
2. The RMT has a infrared diodes (like a TV remote control, but at a different frequency). It is a purely active tracking system, it does not track the prism. The instrument has a tracker scope in addition to the main optical scope. The tracker can detect and follow the the infrared signal from the RMT. It aims the instrument horizontally and vertical to the same point on the RMT, but because the optical and tracker scopes are not exactly aligned, when you look through the scope it probably looks like instrument is not aiming at the centre of the prism. The collimation routines take care of the angle difference, so that the reported angles will be correct to the center of the prism. A service centre can also mechanically adjust the alignment of the two, because if they are far off, the distance measurement from the instrument to the prism (this has nothing to do with the tracker or RMT - these are only for control of the instrument pointing) may be incorrect, or I assume if it is real bad, not get a reading.
3. Completion of correct collimation should fix this.
4. Yes.

First question is which rmt do you have? The ones for that instrument are about 6-8" long. The diode should be under the prism and on one side, don't remember which. Does the red light flash bright and steady on it?

Setting out means staking out. Remember, these instruments come from Sweden.

The gun locks on the diode. Notice it's offset the same amount from the center of the prism as the tracker on the instrument. If you look thru the instrument while it's locked onto the rmt the crosshairs will probably not be centered exactly on the prism. The collimation routine stores the offset so the instrument corrects for that when in auto lock. When adjusted correctly, if you sight the center of the prism in manual mode and set the HA to 0, then turn on autolock, the instrument will move slightly to lock onto the diode, but the HA will still read 0.

The track light is so the rod man can see where the gun is pointed. When staking points, you can have the gun turn to the point and then walk to where the lights are and it will automatically lock on.

I don't have any experience with that particular model of instrument. I don't think that it was Geodimeter's most popular. I do have experience with another model of Geodometer's robots, the 600 series, which was rebranded the Trimble 5600 c.2000. So if you've got a Geodimeter you have a gun that is roughly 20 years old. Survey robotics was in it's infancy back then. So if it doesn't perform like the new ones do it 's partially because they didn't go quite as fast back then, a partially because it's old and tired.

The Geodometers track the led diode and shoot distance to the prism. There is a 1)tracker and 2)EDM on the instrument that is seperated by exactly the same distance that the diode and the center of the prism are on the target. If the gun can't see the diode it will not track.

It is normal for the gun to be pointed slightly off the center of the prism when tracking. There are sensors inside the telescope that can't be on the optical center (or they would block the vision) . I'm not sure of all the details, but I know that what you are seeing is normal.

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Is this the RMT you have? The LED is on the left and this is what the tracker follows. There is a routine in Menu 5.2 for calibrating the tracker to the instrument axis.

Although we traded the 4400's in a long while ago I still have the handbooks and two of the RMT target units, in case anybody is interested.

Yes Chris, the RMT I have is identical. Despite the age of this equipment, it seems to be brand new spares or something as it does not appear the gun base or RMT have ever been installed on anything.

So, just so i can be clear here, the tracking scope that tracks the diode will shoot distance to the center of the RMT, not the face of it? The diode is recessed in such a way that the distance will be the true center of the RMT?

Then there are calibration routines that basically shoot the diode for HA/VA and use the calibration value to add to the HA/VA? I guess in the CNC world, we call this an offset. I am just curious how you verify that the values from the autolock shot are consistent with a manual shot?

I do have the entire manual that seems to walk through most of the setup but the book seems somewhat tailored to having general knowledge of how these work.

As well, with another ignorant question, the prism constant is the offset between the centering point in the prism and the back of it? How is distance determined? Is the distance shot determined off the mirror surface in the prism, then the constant is added in the gun to get position to the true center of the prism.

bob james, post: 392962, member: 12050 wrote: Yes Chris, the RMT I have is identical. Despite the age of this equipment, it seems to be brand new spares or something as it does not appear the gun base or RMT have ever been installed on anything.

So, just so i can be clear here, the tracking scope that tracks the diode will shoot distance to the center of the RMT, not the face of it? The diode is recessed in such a way that the distance will be the true center of the RMT?

Then there are calibration routines that basically shoot the diode for HA/VA and use the calibration value to add to the HA/VA? I guess in the CNC world, we call this an offset. I am just curious how you verify that the values from the autolock shot are consistent with a manual shot?

I do have the entire manual that seems to walk through most of the setup but the book seems somewhat tailored to having general knowledge of how these work.

As well, with another ignorant question, the prism constant is the offset between the centering point in the prism and the back of it? How is distance determined? Is the distance shot determined off the mirror surface in the prism, then the constant is added in the gun to get position to the true center of the prism.

The tracking scope follows the diode and centres on it. That should leave the measuring beam pointing directly at the centre of the prism. If you are using the standard Geodimeter prisms, as illustrated in the photo, (or the larger standard ones - they have the same constant) then the distance measured is to the CENTRE of the block RMT target (ie. above the mounting screw, but 10mm in front of the back face of the target (target is 20mm thick). It doesn't measure to the diode; the recessing is just to prevent clumsy surveyors (is there such a thing??) knocking the end of the diode.

There are two separate calibrations. the first one is to calibrate the ha/va/tilt axis of the measuring head (ie. face left and face right, etc with the values stored in the instrument and applied to all future readings. The second calibration ensures that the manual pointing and the automatic pointing are the same. Visually they can appear to be a little bit off, but the stored value for this calibration applies the correction automatically to all readings.

A quick check is to take a manual shot and note the values. Then do the same on auto and compare both the answers and the pointing as observed through the scope. Even if it appears visually "off" then the answers should be the same. If they are significantly different then the Menu 5.2 calibration is needed.

The prism constant is the value that needs to be added to the observed value such that it gives the true distance to the centering point. Geodimeter designed their systems so that the constant was zero, hence what you shoot is what is true. Generally their instruments will also give true readings to reflective targets without any additional constant. NOTE: this doesn't apply to GDM 360 degree targets which have very small constants (typically around 1-2mm) but you shouldn't be using those for high precision work in any case.

Also, the movement speed of that instrument will be much slower than a current model... My S6 spins much faster than my Geodimeter 650. When the RMT is close to the tripod, you have to move slower or it will lose lock.
You will learn the dance moves and the tempo as you get time in using the equipment.

OK, I spent some hours reading the books and doing testing. Maybe I am picky but I find both the books and machine to be rather tricky as you seem to need to have several cheat sheets around for all the F functions, menus, and sequences.

Anywho, during testing, I determined that the gun, when shooting the RMT 4000, wants to audio alert at the center of the yellow arrows, not the prism itself. It is actually shooting the prism because I removed it and all feedback was lost. So when I shoot the RMT, I sight the center of those arrows for a manual measurement. I verified that the elevation and horizontal distance is accurate. I then switched to autolock mode and the gun shot the same point and I got the exact same values back in autolock.

This seems odd to me but I can only guess that the RMT was designed to have the same offset from that arrow center to the prism as the gun offset from the telescope to the EDM gun? Just a guess here. In any case, I need to make sure this is functioning as intended?

I chased down the collimation procedure and verified it was set to zeros so after that adjustment, I think the values were about .003 and .0006 for V/H adjustment with a max deviation of .02 so I am well within the limits. I was unable to yet calibrate the tilt axis.

As I read through my books, I realized that the previous mention of not having the COGO program was both valid and spot on in terms of what I need. That program would probably be what I mostly need and don't have, now leaving me to ask how the heck I use this gun without apparently any math tools on board? I can only hope there are some basic phone aps or something available? What I basically need it for is the plot points and elevations for buried lines, and to establish more points along property lines or offset points. Given for instance I need to back set a gate 30ft from the property line. That property line is 1000ft long. I would want to establish points closer to the construction site, and the relevant 30ft set back. I am sure I can sit down with a pencil and calculator but that seems a bit insane when using a total station.

Also, maybe some ideas on a simplified method for setting out? I need to reference all my points back to property pins for any future locating. Some of this work is not so much creating points for construction now as much as creating points to use at a much later date when I need to relocate them accurately. With the limited functions in the gun, I was thinking about just centering over a North pin, then shooting the South pin, and establishing that as a zero line for my N/E reference? I am not quite sure why you need multiple reference points before shooting? I know you could not in reality be perfectly setup over a hub every time, leaving some deviation. I am not yet sure how those numbers get crunched.

Now you're talking software. I think ideally you'd want to have a data collector with some surveying software and also a desktop/laptop with an AutoCad type software. You might be able to find something on craigslist/ebay.

The measuring head and the telescope are offset, hence when you point at the centre of the yellow arrows the measuring head is aligned with the prism centre.(and the sensor is aligned with the LED).

As I recall from your earlier posts you were just wanting to do fairly simple things with the instrument, so you might not need to go into additional software. Assuming you have that property line defined on the ground and the points you want are related to that line by offsets (ie. the property line can be used as a grid X or grid Y) then the basic instrument display will give you direct XY values. In P0 (switch on mode) the display gives HA,VA,SD, enter scrolls down to HA,HD,VD, enter again scrolls down to X,Y,Z.

So if you set on a known position on the baseline and put in the XY coordinates of that point, MENU 1,3, and set the bearing of the line to be 0 or 90, or 180 or 270, the the instrument will give target readings as coordinates relative to that point.

If you need additional stations then when you measure them record the coordinates from the screen AND the observed angle. Set on the next station, enter those coordinates and set the backsight angle to the inverse of the foresight you recorded. Instrument will then display any points measured in the same coordinate system. (Set backsight value using F21.) Remember to measure coordinates to the backsight to check they are what they should be.

This isn't as quick as the on-board COGO but it works well for a straightforward job.

A general comment on the block RMT targets. If you are using these for precise measurement by holding the block against wall faces, etc. then be aware that the instrument is pointing at the FACE of the block, even though the measured distance is to the centre of the block. In normal use on a rod the target will be held (I hope) square to the sightline, but against a wall it will not. For most purposes it doesn't matter but for critical dimensions you may need to apply a manual correction for any offset to the side of the target (i.e. if you were working along a wall face running away from the instrument, offset being -10mm x tan (angle to normal) as well as the 35mm offset for the half width of the block. Typical example would be the side walls of a swimming pool with the instrument set in the pool and near one end.

chris mills, post: 393104, member: 6244 wrote: Typical example would be the side walls of a swimming pool with the instrument set in the pool and near one end

I agree that this exemplifies the concept, but in my experience it's hardly what I'd call "typical." I have yet to set up an instrument in a swimming pool, empty or otherwise. (No criticism, just a comment on how "untypical" surveying inside a swimming pool would be for me.)

Thank you again guys! XYZ values would be hugely helpful but yet again, I could find nothing like that in the manual so I will do some testing. I don't intend to shoot a swimming pool anytime soon but if I understand correctly, you are basically referring to the shot being at true center of the block and a situation where the block would be help flat against a wall rather than closer to normal to the sight line of the gun?

In any case, I will certainly test the XYZ mode as that should get me numbers I can work with quickly. Yes Chris, you are correct that I already have defined pins and just need to add more, both on the line, and offset. I am curious if this would be easiest by setting up the gun centered over one of the pins? I know for line of sight reasons, I will need to move the gun to a remote point but I guess I should define that new point from my reference pin, then generate that new point in the grid for back calculation?

OK, I have tried about everything to switch to XYZ mode and nothing seems to work. I did generate a new display with my desired values but in the list of display values in the book, there is nothing about XYZ. Is there another way around this?