Author Topic: more fun with dems  (Read 531 times)

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cadtag

  • Swamp Rat
  • Posts: 1012
more fun with dems
« on: September 02, 2016, 10:35:47 am »
I'm still having fun with Miami Beach....  City provided a raster DEM on a 5ft grid as a tiff.  that came in just fine, and looks great as contours.  However when I check the properties, I'm seeing a minimum elevation is the negative 2000's.  A max elevation of 26' sounds right, and so does mean elevation of 4.9 but minimum??? and a max slope of 65,000% ??  that ain't right.  so there's some bad data obviously. 

The question is, how do I quickly locate the area(s) that are funky?  It would be nice to know that they are not in an area I care about, or conversely that they are..
The only thing more dangerous to the liberty of a free people than big government is big business

mjfarrell

  • Seagull
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Re: more fun with dems
« Reply #1 on: September 02, 2016, 02:13:39 pm »
I'm still having fun with Miami Beach....  City provided a raster DEM on a 5ft grid as a tiff.  that came in just fine, and looks great as contours.  However when I check the properties, I'm seeing a minimum elevation is the negative 2000's.  A max elevation of 26' sounds right, and so does mean elevation of 4.9 but minimum??? and a max slope of 65,000% ??  that ain't right.  so there's some bad data obviously. 

The question is, how do I quickly locate the area(s) that are funky?  It would be nice to know that they are not in an area I care about, or conversely that they are..


one could load that DEM into QGIS and extract the contours from it, then after adding those contours to the C3D surface model exclude the bad elevation(s)
why not use the LAS file you had instead?
Be your Best


Michael Farrell
http://primeservicesglobal.com/

cadtag

  • Swamp Rat
  • Posts: 1012
Re: more fun with dems
« Reply #2 on: September 02, 2016, 02:30:26 pm »
City supplied DEM is more current, (and since it's theirs, they can't argue about what's in it  :-) )

I rebuilt the surface, excluding everything below zero, which took the bad info out of the picture, but it would still be nice to zoom quickly to the 'odd' areas, without having ti visually search for peaks and valleys in the contours. while  -2500 is an extreme, i've found other surfaces from vendors/surveyors that have odd numbers that don't fir reality, and being able to quickly figure out where it is would be handy.
The only thing more dangerous to the liberty of a free people than big government is big business

mjfarrell

  • Seagull
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Re: more fun with dems
« Reply #3 on: September 02, 2016, 02:52:48 pm »
City supplied DEM is more current, (and since it's theirs, they can't argue about what's in it  :-) )

I rebuilt the surface, excluding everything below zero, which took the bad info out of the picture, but it would still be nice to zoom quickly to the 'odd' areas, without having ti visually search for peaks and valleys in the contours. while  -2500 is an extreme, i've found other surfaces from vendors/surveyors that have odd numbers that don't fir reality, and being able to quickly figure out where it is would be handy.

then don't exclude anything
build surface

then do  elevation analysis set ranges to hi-lite the areas (elevations) you question

then do  slope analysis set ranges to hi-lite the areas (slopes) you question

evaluate after each....
Be your Best


Michael Farrell
http://primeservicesglobal.com/

BlackBox

  • King Gator
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Re: more fun with dems
« Reply #4 on: September 03, 2016, 12:34:05 pm »
... Or just paste the original Surface into a secondary Surface, change the latter to exclude below a certain elevation, and simply do a volume Surface with color banding?
"Potential has a shelf life." - Margaret Atwood

Novarese

  • Mosquito
  • Posts: 18
Re: more fun with dems
« Reply #5 on: September 08, 2016, 08:51:05 am »
I'm seeing a minimum elevation is the negative 2000's

Seems like there are "no data" zones, sir, but I'll be 100% sure checking out that Dem: would you share the City link to the Geotiff..?

cadtag

  • Swamp Rat
  • Posts: 1012
Re: more fun with dems
« Reply #6 on: September 08, 2016, 10:03:17 am »
Sorry, I had to make a special request and get approval from city management, so I don't feel comfortable re-posting.
The only thing more dangerous to the liberty of a free people than big government is big business