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Question for you Topcon guys

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Ok, here’s a question for you Topcon guys. In magnet field, when setting up a job in SPC it gives you the option to check a box that says “use grid/ground”. What does checking that box do?

Posted : December 8, 2022 6:20 pm
Norm Miller
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It allows the user to add a grid to ground configuration onto the state plane coordinate system by user defined grid to ground parameters. There are several options to define the ground parameters. I recommend leaving it checked off resulting in state plane grid coordinates. This is particularly true if working with a geographic low distortion coordinate system such as those designed for SPCS 2022 as SPCS grid is ground for most all intents and purposes.  


I read in another post where there is concern that State Plane coordinate inverses do not match a total station measurement using a scale of 1 I assume. I suppose it is known that you can use an average project height scale to put you on the grid as you measure on the ground. In my state the worse it gets is 0.1 ft. in 1000 ft. but its usually less than 0.04 ft in 1000 ft. So for the sake of discussion let's assume we are in Estes Park, CO where the error is 0.4 ft. in 1000 ft. in CO N zone. Using the NGS NCAT tool

for location and ellipsoidal height input we see that the combined ground to grid scale factor is 0.99959128. So a 1000 ft. ground measurement = 999.59 grid inverse when using that scale in a total station. This will eliminate having to deal with state plane vs. calibrated ground coordinates in Estes Park at an ellipsoid height of about 2350m. Incidentally, by plugging in different heights into the tool we can see that a person can use the average height scale between 2250 and 2450m (about a 600 ft. height range) and not have more than 0.02 ft. error in a 1000 ft. ground measurement due to scale. 

This post was modified 2 months ago by Norm Miller
Posted : December 8, 2022 7:03 pm
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If you're surveying around a section, you better apply a ground factor. Especially if you're above 1000 Feet elevation. If your going a small lot survey wouldn't matter much. But understand grid vs ground

Posted : December 8, 2022 10:26 pm

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When this box is left unchecked your EDM distances will be computed from ground to grid using the CSF computed at each setup by your chosen projection and elevation. By checking this box you are directed to enter a user defined single scale factor for the project.

Posted : December 9, 2022 3:02 am
Field Dog reacted
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Thanks for the responses. I’ll probably leave it unchecked because I like to keep everything in a SPC job as SPC. 

Posted : December 9, 2022 8:42 pm