DEM has 'grid' distortion to it, and makes the calculated slope map for it unusable.

397
2
11-10-2012 12:43 AM
Highlighted
New Contributor
I'm sure this question has come up before, but I can't seem to find it. I'm not entirely sure what to search for.

I am using ArcGIS 10.0

[ATTACH=CONFIG]19197[/ATTACH]

I have a DEM of a coastline. As you can see in the attached image, it has a grid overlay to it. If I understand correctly, this is because it was calculated via nearest neighbor? That's not so important since I don't have the original data, only the resulting DEM - the grid is annoying, but if I zoom in on any part of the grid the "line" shrinks, so it doesn't actually seem to impact any of the elevation data points. So I can live with it.

However!

When I create a slope map, these "infinitely thin" grid lines suddenly become quite large, and ruin the data. The second attached image should show what I'm dealing with (in this case, it's a curvature map). I'm using Spatial Analyst -> Surface -> Slope.

[ATTACH=CONFIG]19196[/ATTACH]

I have a hard time believing there isn't a workaround for this, but I just have no clue what it might be. If anyone could help me out, I would be almost infinitely grateful.

Regards,
David
Reply
0 Kudos
2 Replies
Highlighted
by Anonymous User
Not applicable
Original User: erictrice

David,

Those lines are now "IN" the data.  You are spot on regarding Nearest resampling.  Sorry to bring bad news, but you need a different DEM if you can't get the original one before someone resampled it incorrectly.  It most often is because someone projected the data and resampled it with defaults even though the resampling parameter specifically says don't use Nearest for surfaces such as elevation.

""The NEAREST and MAJORITY options are used for categorical data, such as a land-use classification. The NEAREST option is the default since it is the quickest and also because it will not change the cell values. Do not use NEAREST or MAJORITY for continuous data, such as elevation surfaces."

Best of luck,
Eric

Reply
0 Kudos
Highlighted
Esri Esteemed Contributor
Hi David,

I would try resampling the DEM using 'MAJORITY' resampling technique to see if that cleans up the areas affected by the GRID lines.
Reply
0 Kudos