0

Using ArcGIS Desktop, how do I extract a certain area (uniform 1 km from the entire coastline) from a particular year's DEM image?

enter image description here

  • Assuming you already have the DEM to extract from, buffer your coastline by 1km then use Extract by Mask (spatial analyst required) resources.arcgis.com/en/help/main/10.2/index.html#//…. Buffering would work best if the coastline is in a projected coordinate system; be sure that the DEM and buffer have compatible spatial references, preferably the same spatial reference to avoid on-the-fly projection problems. – Michael Stimson Nov 22 '18 at 4:33
  • Welcome to GIS SE! We're a little different from other sites; this isn't a discussion forum but a Q&A site. Your questions should as much as possible describe not just what you want to do, but precisely what you have tried and where you are stuck trying that. Please check out our short tour for more about how the site works. Thanks. – PolyGeo Nov 22 '18 at 5:26
  • @MichaelStimson I have attached the image . Can you please tell me how to buffer 1 km from the irregular shape coastlines in the picture? – Rohan Kar Nov 22 '18 at 8:28
1

To achieve this you would need to use a combination of raster processing tools, a bit of editing then buffer and extraction.

The Initial workflow would be this model:

Model

Notes:

  • IsNulll creates a binary mask of land and nodata.
  • Majority filter (set neighbours to use to EIGHT) removes small pixels of nodata
  • Focal Stat tool is set to SUM values and this captures the edge
  • Reclassify allows you to pull out specific pixels at edge and convert rest to NODATA
  • Convert the reclassified pixels to a vector line

The output would be this:

Polyline

Note that there was nodata in the middle of the DEM so these have come out and generate polylines, you would need to select and delete these out, also delete the obvious edge of raster lines (may require you to split the line with split tool) so you are left with just the coastal edge.

Then as Michael suggests buffer the polyline (make sure you set Dissolve type to ALL) and then use extract by mask, the final output is as below:

masked

Red line is the polyline coastline you had edited, grey is the extracted section (1Km) and background is the source DEM data.

  • Sir, Can you please elaborate me on how to create a binary mask of land and no-data? – Rohan Kar Dec 11 '18 at 7:33
  • 1
    Its the very first tool in the model, you use IsNull, see help file on how to fill in the parameters (which is easy). This will create a binary raster (1 and 0) where there is data (regardless of elevation) and nodata. – Hornbydd Dec 11 '18 at 9:48
  • Sir, I got the 1st step. Now I am getting stuck in the reclassify tool, where my doubt is why we have to replace only the old 5,6,7,8 values to 1 and not others? Can you please elaborate. – Rohan Kar Dec 13 '18 at 6:51
  • 1
    You should explore with any other combination of numbers and prove to yourself what happens. I chose those values (the result of a local sum) as I felt they best captured the edge. – Hornbydd Dec 13 '18 at 10:22
  • 1
    So have created a polyline edge but when you run the buffer tool it does not create a buffer? This seems like another unrelated problem which is a question in it's own right requiring you post a question showing your input data and the parameter settings of the buffer tool. Telling me it has not worked without showing the evidence is almost impossible for me or anyone else to answer. – Hornbydd Dec 13 '18 at 11:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.