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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: DEM Density Vs Orthophoto accuracy |
| Date: |
07/27/2003 01:40:01 AM |
| From: |
Jayachandran Mani |
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Hi sudhagar,
As I had mentioned previously, DEM density is no way
related with orthophoto accuracy. Only the DEM
accuracy matters. If the elevations are not correct
the positional accuracy of orthos will vary. As an
example, a 3m variation in DEM height may induce about
80 cm to 1 m positional shift in your ortho.
DEM density should be decided based on the terrain
only. It can be even 100 m grid with breaklines or 10m
gried with breaklines. You cannot have any uniform
density for all terrain. Professional judgement need
to made in selecting TIN points
Jay
--- Karen Morley <kmorley@lizardtech.com> wrote:
> that will really depend on the terrain involved.
> One factor for distortion is relief displacement so
> if you have an area where there a big differences in
> elevation or uneven terrain surfaces a tighter DEM
> and the addition of break lines will be required to
> improve accuracy whereas if you have an area that is
> relatively consistent, such as midwest plains, you
> can get away with a less accurate DEM. If you are
> concerned about map accuracy you should consult a
> photogrammatrist familiar with National Map Accuracy
> standards through an organization such as ASPRS.
>
> -Karen
>
> -----Original Message-----
> From: sudhagarn [mailto:sudhagarn@geofiny.com]
> Sent: Friday, July 25, 2003 2:29 AM
> To: gislist@geocomm.com
> Subject: GISList: DEM Density Vs Orthophoto accuracy
>
>
> Dear Community,
> I would appreciate if anyone can clarify my doubt.
> what is the impact of DEM density on Orthophoto
> accuracy.
> Will DEM density vary terrain to terrain to acheive
> same level of ortho accuracy?
> To acheive cetain ortho accuracy what is the
> appropriate DEM density for any type of terrain.
> Of course,other factors like scanning ,DEM ,EO
> accuracies also will have impact on Ortho accuracy.
> But I like to know the Impact of DEM density alone
> on Ortho accuracy.
>
> Thanks in advance,
> sudhagar
>
>
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