We have two recent jobs that need elevation information and began by looking at Google elevations for planning, which I'm told is generated by the public available DEM's. I was also informed these were generated by using quad sheet info. One of the projects was an elevation cert in a Zone A which needs a BFE. For that one the Google elevations ended up being 5 feet low for the house, which was a nice surprise, and Google had the river quite a bit west of where it is, although it may have moved since the DEM's were generated.
The other one was a Dam project, we just did some preliminary cross sections and they were flatter than the dam and this time over 5' off vertically.
Is it true that the DEM info is what Google uses for elevations and is that data taken from quad sheets?
The elevation cert is located on a 20' contour quad and the Dam is located on a 40' contour quad.
It is my understanding that Google will not reveal the source of the vertical datum it utilizes. It is my personal experience that it can vary tremendously from ALL survey determined values. I belive there has been discussion on this forum of people finding it to bee hundreds of feet off. Google itself states that displayed elevations are a "general reference tool."
It doesn't matter what Google Earth shows, ALL FEMA related data must be determined from the FIRM's, regardless of reality...
I wouldn't use Google Earth elevations for anything more than a general reference. I have seen them be fairly accurate from a general elevation standpoint 2'+/- and have also seen them several hundred feet off. Use each tool, office or field, in accordance with it's intended use.
I don't use Google for anything beyond making some pictures, some very preliminary plots, and using them for rough acreages. It's nice for planning.
The engineer will no doubt use it to plan where the cross sections will need to be for determining the BFE but that's about it. I've never got any good data from DEM's or Google.
I was just curious if they are using DEM data or if like the photos they might include some large mapping data they can get their hands on in the area.
A good source for lidar data is https://viewer.nationalmap.gov/basic/?basemap=b1&category=ned,nedsrc&title=3DEP%20View or
https://coast.noaa.gov/dataviewer/#/lidar/search/
makerofmaps, post: 408900, member: 9079 wrote: A good source for lidar data is https://viewer.nationalmap.gov/basic/?basemap=b1&category=ned,nedsrc&title=3DEP%20View&apos ;"> https://viewer.nationalmap.gov/basic/?basemap=b1&category=ned,nedsrc&title=3DEP View or
https://coast.noaa.gov/dataviewer/#/lidar/search/
If I'm reading that correctly, I'm in the "blank" area for all of that data
MightyMoe, post: 408905, member: 700 wrote: If I'm reading that correctly, I'm in the "blank" area for all of that data
Same here - no coasts in AZ...
I have found that they sometimes utilize information that is not the same as the USGS DEM. Not sure where they get the data. It's a mosaic from many sources for sure.
Seems that there is a lot of data being used with mysterious origins.
I only use GE for scouting jobs before quoting.
I used to use it for elevations by getting a rough elevation in the center of an intersection and use that to base my topo from ONLY IF the subject WAS NOT in or near a flood zone. Instead of using an assumed number I would use something close based on GE but clearly the survey would state this. I no longer do this because with GPS it is too easy to put things into NAVD.
Around my area GE is very good though with elevations. Very close. Link someone above said, usually +/- a foot or two depending on how flat/open things are.
Have you tried the SRTM Dataset. It's been revised and voids filled. We're too far north for it. If I was google SRTM would be the most consistent for worldwide consumers. http://www2.jpl.nasa.gov/srtm/ .
Sent from my iPhone using Tapatalk
I am amazed at how good google earth's elevations are. I've got in the habit of using it for just a very rough check that a Navd88 elevation has been established properly on site, just hover the mouse over an area on a street or hardscape and compare, they're usually right on