This is a rather in-the-weeds question for the ??ask a surveyor? forum. I??m a mechanical engineer doing surveying as a hobby on my own property. I??m using Trimble General Survey software on a Trimble TSC3 collector and a Trimble S6 DR+ robot. I have all the manuals, and I took an introductory surveying class from the late Francis Moffitt at UC Berkeley in 1977. I also have more recent survey textbooks.
I have several property corner monuments that were set by a licensed surveyor as shown in the attached screenshot, so I??ve got the backsights. My objective is to locate some landmarks such as water well bores, power poles, culverts, and develop some topological mapping data.
My basic question is: Given the prior survey data and plat map, what is the recommended workflow?
In particular:
I gather that I need to key in the data for the backsight points. But here??s my first puzzlement: The General Survey software is impressively powerful and comprehensive, yet it doesn??t seem to have a way to input points using bearing distance from another point. In contrast, when keying in a line, it offers the method of inputting the bearing and distance from a point; yet I don??t see a way to make a point from the end of the line. So do I really need to pre-calculate the X-Y coordinates of all of the property corners from the bearing and distance data?
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COGO --> Compute Point --> Bearing & Distance should get you what you want.
So do I really need to pre-calculate the X-Y coordinates of all of the property corners from the bearing and distance data?
Yes, this is what I do...
Azimuth from point A to point B is azimuth from point B to point A plus or minus 180 degrees as needed to keep the total between 0 and 360.
Thank you Rover83 and RADAR! Got it!
Bill93: Thank you for that reminder. I forgot to mention that I took trig in high school; it was summer school in 1973. That was a while back and the memory has faded.
I have a question about V.dist, but first some more background. I have the instrument positioned conveniently, but not on a control point, and I'm doing a Resection instrument setup. All of my control points are property corners for which I have "known" X-Y values but not elevation. For the first control point, I set the elevation to the rough number given by my iPhone's GPS as a datum point. So I'd like the rest of the V.dist values to be measured by the instrument. So my question is: Why does the V.dist field on the screenshot below not have an option to measure it from the Start point, not enter it a priori? This screenshot is from CoGo --> Compute point. What is the correct workflow for this situation?
@bernardc That screen is asking you for the difference in horizontal and vertical distance that you want. You have told it to calculate a point 179.115m away from a specific point and it is giving you the option for the vertical distance difference that you want. If you leave it at 0.00 your new calculated point will have the same elevation as the point you are originating from.
Some very quick hints:
Your version of Access is way old - some answers you get may not apply to you.
Calculating elevation is optional a resection
Null and zero heights can cause issues (null is not the same as zero)
You must enter instrument and pole height correctly
You can use a height only point (benchmark) in a resection
You can choose whether points are used for 3d,H or V only in the calcs
You could edit the point to add what your iphone says
Save control points with new names if you edit them to add elevations
Hope this helps
=Jim=
@lurker Yes, I get that. But I want the instrument to measure V.dist. I'm saying that CoGo --> Compute point won't do it. What is the automatic method for doing what I'm describing?
@jim.cox My Access version is 2017.24 as shown in the screenshot below (which I had to get manually because Ctrl-s doesn't seem to work for the About screen). The copyright on startup is 2019. Not terribly old, I think.
I did enter the target height accurately. But for instrument height there's a check box for Measure instrument height. That sounds like it'll get the instrument height from the first backsight point, unless I'm misunderstanding.
I'm using the rough GPS elevation for the first backsight point only, not any others. I want all the other elevations measured using that first backsight point as the datum.
This note in the manual might be a clue:
Note – To determine the elevation of a point with known 2D coordinates, perform a station
elevation once you have completed a station setup.
The instrument height is the height above your point of occupancy. The vertical distance is the difference of the mark aka your prop corner and your instrument mark if you include the rod height at the BS and instrument height. If you just do a vertical distance its going to be the height if differ ce of the scope parallel to gravity and you prism itself so 90 degrees vertical angle. Go to key in point key in the elevation of the number of the property corner you made the elevation with IPhone. Store that. Then before doing the resection measure your rod height and i strument height. Do the resection. Because of being an older version. If it doesn’t compute your elevation at your instrument. Simply add the elevation of corner to your prism at rod. Shoot the vertical distance add or subtract then subtract the instrument height. Now you have a elevation at your instrument point. Pay attention to the signs. You can also you o/h a/h o/a oscar had a hardy old a$$! And use the same info but solve via triangles to get different heights of scope and prism and the. Reduce prism to mark and scope to mark. There might be a station elevation or something like that in the software that you can perform after the 2d resection. I surely can’t remember. Make sure you are inputting elevation not height AKA ellipsoid height. I assume you made up xy values. Or northings easting and computed by bearing and distance the rest from the plat. Another routine that might be better for your work is refline. I don’t remember if thats in that version. But basically your two property corners established a line. You shoot both like a resection and everything is based off of that baseline. I believe you can hold one vertical point that way of any of the two and make that work as well.
