# Forum

### Author Topic: Problem with DEM measurement (tilted polygon)  (Read 2247 times)

#### ericktreichel

• Newbie
• Posts: 12
##### Problem with DEM measurement (tilted polygon)
« on: March 09, 2019, 01:10:14 AM »
Hello everyone!
I have a DEM which is the subtraction of two others (which means the height difference of sand that came up in a month on the spot). And I need to calculate the volume that a certain area has in that DEM.
However, when drawing a polygon, it is tilted, I can not leave the 4 vertices of it with coordinate Z = 0.
How can I measure the entire volume in a given polygon in DEM or orthomosaic?

(My problem is the same of this guy who did not get an answer. (https://www.agisoft.com/forum/index.php?topic=6631.msg32044).)

Thank you!

#### Dave Martin

• Full Member
• Posts: 170
##### Re: Problem with DEM measurement (tilted polygon)
« Reply #1 on: March 09, 2019, 11:00:43 AM »
Erick,

Personally my go-to tool for something like this is Surfer - I'd just take the two DEMs and subtract them in Surfer using a polygon (drawn or imported) as a bounding/blanking line. You could also use Cloud Compare (clue is in the name!), and probably also in QGIS, ArcGIS, AutoCAD Civil, TBC...

Dave

#### ericktreichel

• Newbie
• Posts: 12
##### Re: Problem with DEM measurement (tilted polygon)
« Reply #2 on: March 09, 2019, 12:54:29 PM »
Erick,

Personally my go-to tool for something like this is Surfer - I'd just take the two DEMs and subtract them in Surfer using a polygon (drawn or imported) as a bounding/blanking line. You could also use Cloud Compare (clue is in the name!), and probably also in QGIS, ArcGIS, AutoCAD Civil, TBC...

Dave

My teacher actually suggested using Surfer to accomplish this ...
Initially I had a preference for being able to calculate by Metashape itself, because it would be a highlight for my work to "use only Metashape to perform all the steps" (clouds, DEMs, measurements).
But if I can not get a confirmation if the use of the metashape volume measurement tool is reliable, I believe I will have to use Surfer.

Erick

#### Dave Martin

• Full Member
• Posts: 170
##### Re: Problem with DEM measurement (tilted polygon)
« Reply #3 on: March 09, 2019, 01:33:08 PM »
Erick - if you've got access to Surfer, I would use that and then you could back-compare to result from MetaShape - which may well give the same answer!
cheers/Dave

#### ericktreichel

• Newbie
• Posts: 12
##### Re: Problem with DEM measurement (tilted polygon)
« Reply #4 on: March 10, 2019, 01:39:20 AM »
Erick - if you've got access to Surfer, I would use that and then you could back-compare to result from MetaShape - which may well give the same answer!
cheers/Dave

Yes ... great idea !!
The problem is that I do not know how to use Surfer yet, and my deadline for delivery is very close ... but I will try to learn here to make that comparison.
Thanks Dave!