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I've been blindly using Corpscon to convert from NGVD29 to NAVD88. Have any of you kind folks found issues with your outputs?

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CorpsCon has a help FAQ for issues surrounding NGVD29 to NAVD88 conversion, and specifically mentions:

Can’t I use CorpsCon to convert survey data from NGVD29 to NAVD88?

In Missouri, yes; but in Louisiana, absolutely NOT! The NAVD88 was developed as a replacement for the NGVD29 because the NGVD29 had become unreliable and out-of-date. The NAVD88 was published for most of the country by 1990, except for those regions of known crustal motion which included Louisiana. In 1992, the NAVD88 was published for Louisiana, but because of the continuing crustal motion of subsidence the lifespan of the NAVD88 benchmark elevations in Louisiana was limited to a few years.

That said, depending on the accuracy needed, you may be able to test your results against something like this modeled conversion from NOAA.

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