Palo Alto benchmarks

MikeTurnrose · Post by **MikeTurnrose** » Tue Jan 07, 2014 3:15 pm

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.

sako · Post by **sako** » Sat Jan 11, 2014 12:31 am

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.

btaylor · Post by **btaylor** » Sat Jan 11, 2014 8:53 pm

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

land butcher · Post by **land butcher** » Sat Jan 11, 2014 9:23 pm

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.

land butcher · Post by **land butcher** » Sat Jan 11, 2014 9:24 pm

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

MikeTurnrose · Post by **MikeTurnrose** » Mon Jan 13, 2014 10:17 am

Thanks for your input everyone.

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

PLS7393 · Post by **PLS7393** » Tue Jan 14, 2014 5:51 am

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.