I'm a big fan of being completely organized.  Therefore, I wanted to lay out my procedures for getting a jobsite set up for a highway project.  Some of these methods may help save time applying them to other areas of surveying/engineering. 

 

All highway projects in my state of Wisconsin provide a control network for each job.  Some times, the state will hand me their calibration so all contractors are on the same page.  Every job I have ever done has been on either a County coordinate system or State Plane.  When I import this data into my drafting software (Terramodel), not only can I see the relationship between my model and the control points (to ensure they surround the jobsite completely), but I can EXPORT the points to Google Earth.  During the export, it asks which county,state, or other coordinate system that your points belong to, and incorporates the relationship between that system and geodetic lat/long to plot the points on google earth.  Looking at a map of a 13 mile jobsite (like the one I attached) can be hard to look at on such a large scale.  The nice thing about Google Earth is that as you zoom in, the points will seperate if they are too close together.  From there, I will do a print screen (control-prtsc button) and paste it on 11x17 paper size in Microsoft word. Then I will pan down and repeat.  I will then print it and tape it together, if necessary, and I will use a red pen or something to add in points that only have vertical data. I have attached an example.  This way a person can drive to within fifty feet of a point by looking at features on the aerial map, "oh, when I see a treeline on my right, the point should be at that intersection" etc.   Having a control plot like that not only organizes a person in the field, but it is a hard copy of the points that were used, thrown out, etc. for that particular calibration.

 

Now that we are ready to calibrate our rover, I want to discuss using a continuously operating reference station network.  Known in Wisconsin as WISCORS, those of you that have used this already love it, and those of you who haven't don't know what you're missing.  Right now the State of Wisconsin WISCORS network usage is free.  You just contact one of the program administrators, and they will add your cell phone # (I recommend getting a phone that gets no calls at all for this purpose) and give you a login/password/server ip address/ip port.  You pair your data collector to your phone (with some technical support req'd) and every time you do a set up rover, it will automatically tell your phone to connect to the state's servers using the internet (phone stays in your pocket, no need to push any buttons) and wala. You are now accurate to 0.02' horizontally and 0.03' vertically. 

If you do get a cell phone call during a calibration or anything, it will kick you out of WISCORS, and you just have to do another setup rover (takes 40 seconds, it is just annoying) 

 

Now calibrate the site.  The best part about Trimble SCS900's calibration feature, is that after you have stored at least 5 horiz/vertical points, you can see the horizontal and vertical residuals for EACH point that you store.  If one point has a horizontal residual of 0.08' and the vertical is 0.01', you can turn off just the horizontal for that point and it will not be used when you tell it to 'Finish the calibration'

The beauty of the CORS network is that you don't have to leapfrog your GPS base station four times (introducing un-necessary potential for error; settlement on each set up)  If you use a geoid model, then you are even more accurate.  I have calibrated 10 - 15 mile jobsites to achieve final residuals to be 0.02' horizontally and 0.025' vertically.  That is a quarter of an inch!!!  Way to go technology!

 

Every jobsite gets DAILY calibration checks stored to ensure the integrity of the control points used, especially after a Wisconsin freeze/thaw winter/spring for those two year projects!  Any questions or added input will be greatly appreciated!!

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Replies

  • Party Chief

    very helpful information...thanks Dean!  just what i was looking for...

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