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Intersection Question


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My brother once in a while looks for marks etc.


While we know the NGS doesn't want reports about intersection stations - he still has this question for everyone:



Can an intersection station, which is a fixed point on a building, remain a valid reference point if it is replaced with and exact duplicate replacement feature.



What order of accuracy must be maintained for an intersection station which needs to be repaired.



About the Mark




About the dome replacement




School history



Edited by frex3wv
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Technically if a point is rebuilt, it isn't the same point - it's destroyed. Practically, I'd guess that a completely rebuilt cupola, dome, or spire won't be close enough.


But if a church spire or cross is removed for re-shingling and replaced without structural modifications, it probably is within an inch or so, and may be "good enough" for the purposes intersection stations were/are used for, when observed from triangulation stations at typical distances of a few miles.


The spec for third order I believe was 1:10,000 relative to other network stations (2-sigma or 95% confidence?), but most observations would have been good to maybe arc seconds, say 1:200,000 precision or 0.3 inch per mile and small changes would be detectable if anybody re-observed to that precision (which NGS won't be doing).


That's a totally unofficial guess, of course.

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I think Bill93 gave a pretty comprehensive answer, especially given the fact that it hardly matters anymore. No-one doing work that requires centimeter accuracy is going to be using an intersection station. What you have to realize is that even the fact that it is listed in the National Spatial Reference System has no bearing on the owner's (of an intersection station structure) decisions of how they might conduct a renovation/restoration of their structure. With a few rare exceptions (the Washington Monument is one), the Federal Government has no legal interest in what goes on when these stations are modified, rebuilt, or destroyed. So the owner is free to do as they wish, most likely in ignorance of the geodetic significance of their structure.

In the case of Wagner's Main Hall, I doubt that anyone will be doing the measurements necessary to assure that the cupola occupies its original position.

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