The use of Total Stations by Millwrights and Machine Erectors is becoming more and more common place . There are those who have used them for over a decade now , and who know just how handy a TS can be for certain tasks . They know how quickly centerlines can be layed out or offset , how fast 90's can be turned etc . , even when pluglines are not available .
The Nikon DTM-352 is a Total Station designed primarily for land surveyors . However , because of it's built-in compensators the Nikon can also be used with confidence for machine layout purposes . The DTM-352 is not a replacement for the Wild N3 Level or Wild T2 Theodolite , but can be an excellent tool to use along with the Wild instruments .
This is the methodology suggested here . That is , first , use a good solid T-Station like the Nikon , with it's excellent built-in Coordinate Geometry software to lay out centerlines and offsets and to check approximate locations of machines surfaces . Then do a 'Final Alignment' with well known 'Industry Standard' tools - the N3 Precision Level , and the T2 , with it's deadly accurate 1-second gun .
Welcome to the Computer
Hello and welcome to this quick computer course . Ha , tricked you perhaps ! Maybe you were expecting another layout course ? No . Machine layout is as easy as pie , to a Millwright . Laying out centerlines and offsets is a piece of cake , a second nature , as we all know .
Using a Total Station is also easy . Learning it is not . Like many of our skills , the learning process simply takes time .
The Nikon is nothing without it's software , simply because a Total Station is ... a Computer , with one big round eye . We'll begin by learning how to use this computer to determine where very particular points in space , exist .
However , I should warn you that we are going to be moving very quickly here . There are many things that should be discussed first , but in an effort to get Millwrights actually using a Total Station for the very first time , in record time , we will leave the finer points , and even some critical points , for another day .
Using a Total Station for the first time is not an easy matter , but , perhaps if we enter into the process with a new understanding , of using 'software and silicon' instead of 2 foot squares and 100 foot Tapes , we may be able to get up to speed in a somewhat smoother fashion .
(should you decide to accept it)
Briefly outlined below is the typical shooting scenario -
1) It's a brand new building , no machines , no plug-lines layed out .
2) Your supervisor wants a centerline layed down directly in front of a machine .
3) He wants you to use the 22F & 22G Columns as your benchmarks .
4) There are pipes in the way and lot's of machine crates on the floor .
5) There's no easy way to use a 100 foot tape (sound familiar?) .
6) A large crate is laying on the centerline - so then we must also offset the C/L .
Not Impossible !
Now , before we begin on how we will tackle this assignment , we should first acknowledge that it is possible to do this the "Old School Way" with tape and tools . Nothing is impossible to a Millwright and jobs like this one have been done uncountable times before . Long before the invention of the Total Station we've done this accurately , time and time again .
The Total Station can make (with a qualified operator and stickman) this job easier and also faster , involving fewer moves . Fewer moves can sometime's translate as , 'less chance for error' .
With every move we make , we also introduce the opportunity for a mistake to somehow creep into the equation . Tradesmen know this , and so nothing get's by a seasoned Journeyman . They will double-check or back-check all work as they go , taking great pride in confidently providing accurate layouts .
Just Do it
Ok , let's just get right to it . We'll pick a spot
where we can easily observe -
#1 ) Both Columns ( 22F & 22G ) at 'floor-level' .
#2 ) A floor area capable of containing 2 or 3 points representing our offset centerline .
We'll set up a tripod , level the Nikon and place a mark on the floor using the built-in Optical Plummet . Always place marks as we go in order to be able to 'trace our steps' , should we need to down the road . This is sometimes referred to as "covering your butt" in case of any future discrepancy between what you did right and what someone may say you did wrong .
Proceed to have your stickman measure the center of the Column as accurately as possible (at floor level), using a Tri-Square . Layout a vertical centerline . Columns are not machined surfaces but we have been instructed to use this structure and so we will do so to the best of our ability .
Have him place one prism at the center point between the web , at each Column , making sure to keep the prism perfectly vertical at all times . This will be our 'Column Center' . It's not perfect but will be within allotted tolerances .
This condensed exercise will restrict our shots to being taken at floor level only . Of course a TS is capable of calculating points at any elevation , but for now we will concentrate on simplifying the process as much as possible by ignoring the 'Z' (elevation) reading in our calculations and layout .
Turn On The Nikon
In the meantime , turn on the Nikon and create a new Job . We'll call it '22F+G + todays date' . Hit the 'Settings' softkey and go through all the settings screens making sure all is as it should be .
Site the prism at either Column , press the 'ANG' button (Angle) and select 'Ang/0-Set' . This will give us a 'Known Azimuth' (zero) . Press the 'DSP' key (Display) until we are in the 'X: Y: Z: ' area of the Display Screen . Shoot the prism center at the first Column and enter it's coordinates into the database by pressing the 'Enter' button .
The Nikon's default is to name this Point "1" . We can easily change any setting's default if desired . Have the stickman move to the opposite Column and then shoot and record point #2 ('2') .
Time For Our First Software Program
Very good . We have Point #1 and Point #2 in our database .
We will now open the first Software Program . Select the 'Menu/CoGo/Inverse/PT-PT' program . The input screen appears , Enter '1' in the P1 field using the keyboard . The Nikon automatically retrieve's the point from the database and presents it to you for viewing . For the P2 input , enter '2' and the Nikon again shows you those 'XYZ' coordinates .
We now see both input fields filled in . Press the 'Enter' key and a new screen appears revealing both the Horizontal Distance between 'P1' & 'P2' as well as the 'Inverse-Angle' that is formed between the Nikon and the line defined by points 'P1' & 'P2' . Write this information down . We cannot record it directly from this screen for some odd reason . Too bad , but it's no big deal .
Time For Our Second Software Program
Next we will delve into our second Software program . This is also in the 'CoGo' (Coordinate Geometry) section . Select 'Line & Offset' and the input screen appears . It wants to know which line we are going to use and which 2 points we are going to use to define that line (or which single point and what the Azimuth angle formed will be) .
Again , very simply enter '1' into the P1 field and '2' into the P2 field . Skip over the Azimuth field by pressing the 'Enter' button . We could use the Azimuth field , and I suggest you try that later , just as a kind of back-check . Both should supply the exact same coordinate results if done properly .
Now , this program's 'Secondary Input Screen' appears . It will ask us to provide a HD (horizontal distance) to shift a point along this line formed by Columns (22F & 22G ) . We want a centerline point , which is exactly half the HD between point '1' & point '2' . The full distance was written down , so divide that number by 2 and enter the exact result into the 'STA' field . Good .
Also skip over the 'O/S' Field (for now) by pressing the 'Enter' button . We will indeed utilize this input field in a moment or two .
Skip over the dVD (vertical distance) input field (just press 'Enter' since all shots are considered to be at the same elevation) . The next screen reveals the result of the Nikon's trigonometric calculations - our all important 'center-point' 'XYZ' coordinate .
However , as you may remember , there is a big crate laying directly on top of this point . No problem . Hit 'Enter' to record this point into the Database , for possible future reference (this will be point '3' in the 'XYZ Database' area ). We can rename this point or , simply add a comment to the point , such as 'CENTERLINE-PT3' in the 'CD' (code) input field . Press 'Enter' again to record it .
Simply Shift The Line
Once recording is done our 'Secondary Input Screen' re-appears . We will use the 'STA' input field again and add enough distance to our centerline point to get a sufficient distance away from that obtrusive machine crate .
Simply add 1.000 meter to the "P1 minus P2 divided by 2" result that we used previously . This will shift our centerline point along the line and away from the crate . Hit 'Enter' twice to get to the final result screen . Hit 'Enter' to record this point ('4') and add a comment if you like , such as "CL-plus-1-meter" .
What's Your Point?
Great , but as any Millwright knows , one point does not give us a centerline . Correct ! No problem , we will use the 'O/S' field to move a point forward away from the 2 Column's centerline at a right-angle , and then again in the opposite direction (see Diagram #1) .
This will give us 2 points , moved along the line formed by ( 22F & 22G ) , far enough to get away from the crate , offset at a perpendicular , and far enough apart to be able to snap a chalk line or to scribe a line into the floor . Perfect !
So , back in the Input Screen we will see the number previously entered is still in the 'STA' Field . Hit 'Enter' to move to the 'O/S' (Offset) field . Pick a distance to get a good solid offset . The bigger the better of course , but for this small job 4.0 meters on either side of the Column Centerline will suffice .
Create An Offset Line
So , enter 4.000 into the 'O/S' input field , and jump through the dVD field and then hit 'Enter' to get into the final result screen . Hit 'Enter' to record this new point ('5') and add a comment such as CL-1M-4M-OS-SOUTH . We're adding the 'South' comment because we'll do the exact same thing next , with a (minus) -4.000 Meter amount in the 'O/S' field in order to move the point in the opposite direction (North) . Record the point .
Back in our Input Screen and we see that the 'STA' field is unchanged . Press the 'Enter' button to get to the 'O/S' input field . Delete the 4.000 entry by using the 'BS' key (Backspace) key and this time enter -4.000 . This will provide us with 2 points , 8.000 meters apart that we will use to form a solid line ... right ?
Press 'Enter' and we see our new point coordinates revealed . This time add 'NORTH' to the 'CL-1M-4M-OS' comment and hit 'Enter' again to record the point ('6') to the database .
Now , we could create another point directly on our Column line , if we like , just as a kind of double check to see if our 2 offset points intersect it properly . Do so by following the steps above , but enter '0' (zero) into the 'O/S' input field . This point should have the exact same coordinates as our previous point #4 ('4') , agreed ? Record it and check later in the 'Data Section' to verify our assumption (point '7') .
Once you've recorded the 3rd point for this new perpendicular offset line , press the 'Escape' key a few times to get back to the Main Display Screen , the 'BMS' (Basic Measuring Screen) . This is where we will move and sight our prisms , in order to mark out each point's exact location on the floor .
Let's Build That Line
Press the 'DTA' key (Data) and in the 'XYZ' area of the Database we will see a list of points . Choose the last one by pressing the 'Enter' key . Observe this point's 'XYZ' coordinates . Write them down . We will use these coordinates to locate points along the floor by positioning our prism .
Press the 'Escape' key twice to return to the 'BMS' . Press the 'DISP' (Display) key until we are in the 'Coordinate' area showing a blank X: Y: Z: ( N: - E: - Z: may be showing instead , depending on how the Station has been setup ) .
Measure to our prism in order to initialize the BMS 'X,Y,Z' again . Unlock the Nikon's Horizontal and Vertical screws and move both body and telescope while observing the 'X,Y,Z' fields changing on the Display . We'll move both components until the coordinates of the point we are looking for , appear in the display . Do not attempt to get the readings exactly right on . 'Ballpark' close is all we are looking for at this particular stage .
Guide your stickman to place a prism anywhere in the Nikon's cross hairs and press the 'MSR' (measure) button . An exact reading of the Nikon's cross hair location (not the prism's) will now appear . Move the Nikon again and measure until the exact coordinates for this point are displayed .
Simply motion to your stickman to move as required and align the prism until it's cross hairs match the Nikon's cross hairs . There . That is the exact location of that particular point .
Now , mark a point directly under the prism's center , onto the floor . Depending on what type of prism you are using , this process can either be a little tricky or very easy . Keep the prism vertical at all times .
While your stickman mark's the first point , go back into the database and retrieve another point . Repeat the above steps until all 3 points are well marked on our floor (points '4' , '5' & '6' ) .
Pull a string or lay a Straight Edge and check that all 3 points are on-line . Snap or scribe the line . If there is any doubt about the line we've just created , or the points we've layed , by all means back-check your work , as always . Use the standard '3-4-5' Measuring Method to check our 90 degree angle .
If the 90 looks good , but you want to back-check the line location , perform the procedure again using a slightly larger Offset , or shoot any 2 points using the 'CoGo/PT-PT' software program and check the results with a measuring tape to confirm .
If it happens there is no room for a simple '3-4-5' check ... use the Nikon ! Select the '3PT Angle' Program , that's also in the 'CoGo' S/W section . Use either Column Point as P2 and any Offset Point as P3 . P1 must be your 1 Meter Offset point that lays on the Column line (point '4' or '7') .
I hope this simple exercise has at least inspired you to try other types of practice layouts . Once you have done a few of them you will find that your confidence level will increase as your skill level rises . We have to start somewhere and the 'CoGo' section is a very good place to begin to get a handle on using a Total Station for layouts .
Cheers & Best Of Luck !