Trimble Business Center

Hi,

I measured a traverse with Access and measured station and target heights to the bottom notch. But I used a custom prism constant.

Now, when I drag'n drop the Job file into TBC 5.20.2 it complains

"The height measurement method is incompatible with Custom prism. The true vertical height method is assumed."

That is nonsense, and from my point of view a bug. If I make sure I have prisms with the correct distance above the tribrach and select that method in Access then TBC is not to change my measurement method, it's not even asking. That is messing up my elevations.

That message is actually confusing and should be rephrased. I also showed that message to my native English speaking colleague and he also would think the message means an i.e. 1.40 m bottom notch is used as 1.40 m true vertical height. Instead TBC does actually convert the value according the formula from the S series manual.

Can you give more information what you are actually using?  I assume you're using the new Trimble traverse prism setup?

I think that if you are using a bottom notch setting, that you must use the standard prism in order for the calculation to work. Otherwise the height of your different/custom prism isn't known by TA or TBC.  Just like the distance from bottom notch to instrument center on the SX and S series total stations is a known constant distance.

I actually have been using the Trimble traverse kit but somebody set it up as custom prism with the correct prism constant in Access.

But the same would happen if I would use a third party prism with the correct distance from tribrach to prism center and the measurement to bottom notch.

It's not that TBC is doing a wrong calculation. It's the fact that the warning phrase is misleading and I actually thought it is using my bottom notch value as true prism height without recomputing it. Until I'd spent some time and checked the values manually. And with the above mentioned formula they do indeed fit.

The phrase should be more like "Bottom notch values will be converted to true vertical heights".

This seems like TA needs to be revised to not allow custom prism with bottom notch height settings.

Definitely not!!!

Bottom notch measurement is much more accurate than a bend tape measure to the prism center. And all the prisms I've used so far had the correct size from tribrach/bottom notch to prism center, so I've always used it.

The warning message in TBC needs to be rephrased. It's insinuating something it is not doing.

And better, TBC would keep and show the bottom notch measurement for custom prisms. That way you could fix typos in TBC instead of going back to TA.

But if you aren't using a Trimble target on this traverse tribrach, TA and TBC don't have a known height of the custom prism you are using. That's why I'm suggesting that custom prism be not allowed with bottom notch.

But there are lots of third party/custom prisms that do have the correct distance. So, removing that option is a no go.

That thread seems to keep moving off topic. TA is not the problem, the TBC warning is misleading.