California Surveyors Forums

The City of Palo Alto published a benchmark list in 1993 which is pretty extensive. However, the datum is on NGVD 29. The City did not adjust the elevations to NAVD 88 that I know of when FEMA redid the FIRMS in 2009. Has anyone used the BMs recently there for an El Cert and converted to NAVD 88 using VERTCON? If so, what was your feeling about the reliability of converting? Thanks.

MikeTurnrose wrote:The City of Palo Alto published a benchmark list in 1993 which is pretty extensive. However, the datum is on NGVD 29. The City did not adjust the elevations to NAVD 88 that I know of when FEMA redid the FIRMS in 2009. Has anyone used the BMs recently there for an El Cert and converted to NAVD 88 using VERTCON? If so, what was your feeling about the reliability of converting? Thanks.

I used vertcon to convert the BM to NAVD88. The city provided me with an elevation 0.1' higher than what the software did. Ironically, the 0.1' difference got the FF at BFE.

I have seen Vertcon, at least in the areas I work here in the Bay Area, to be pretty accurate.

A few years ago Vertcon was described as "use only for topo".
I am not sure if going to different areas would effect the results, but I would test vertcon on agency published bms in both 29 and 88 such as Orange County and LA County.

sako wrote:I used vertcon to convert the BM to NAVD88. The city provided me with an elevation 0.1' higher than what the software did. Ironically, the 0.1' difference got the FF at BFE.

That's scary

Thanks for your input everyone.

I have had pretty decent results with VERTCON the few times I've used it also.

VERTCON is the only conversion tool I use, as it is clean and easy.
Two rules of thumb:
1) Some use GPS to transfer and establish elevations (+/- 0.1') elevations
2) FEMA Elevation Certs only want 0.1' accuracy

So using VERTCON is right in line with acceptable tolerances.