Clip bathymetry raster to land polygon

Question

Hello,

I have a bathymetry raster that contains values for land areas. I would like to clip the raster so that all land values are NA. However, when I clip it to the land polygon, it retains ONLY the land values. 
How do I clip it so that the values OUTSIDE the land areas are retained ?

Thank you !

Juliane

EricRice · Answer

Juliane

I don't think your data is likely to be integer and hence have an attribute table which is required for Extract by Attribute.  If I'm wrong you could definetly do that though.  For the most part, land masses don't go below sea level.  Sometimes they do though....If your area has all positive values for land and negative for bathymetry you could do a Con statement to get everything less than 0.

If you want to do the water feature, you need to create it by using the editing tools. Since you have the land mask already, the Mask button from the Image Analysis Window is your best bet, or the Inside/Outside options in Data > Export data.  (see blog)  If you don't have ArcGIS 10, there is no way to do masking like this; where you get rid of what is under the mask.  Set Null (not a traditional clip tool) may be an alternative where you could set the land pixels to nodata and keep the bathymetry though.  Pre 10, you could only clip and retain what is under the polygon.  If you aren't on 10, you need to manually edit the water boundary in polygon form and use that polygon to clip out the data you want. Let me know your version and I can make some recommendations for earlier versions if needed.

Because of this thread and many others, we just posted a blog about the various ways to clip and mask in ArcGIS.  It's not long, but probably worth reading.

Cliping an image or raster in ArcGIS.

Regards,
Eric

JulianeStruve1 · Answer

Hello,

thank you very muh for replying, I would like to create the water polygon, but how ? And also, could I use the extract by attribute function to achieve the same outcome, by extracting non-land values ?

Regards and apologies that these questions are rather basic.

Juliane

Juliane,
One more way, if you don't want to take the time to build the water polygon or don't already have one...  You must have ArcGIS 10.0 minimum so you can access the Image Analysis Window.  There is a mask function button on the window that performs the type of masking your looking for.  i.e. Keep what is outside the mask.

See Using the Mask button on the Image Analysis window

Terminology differences:
Clip GP tool  - performs clip.  Keeps what is inside the polygon
Extract by Mask GP tool - peforms clip. Keeps what is inside the polygon
Clip Function (Image Analysis Window) - performs clip. Keeps what is inside the polygon
Mask Function (Image Analysis Window) - performs mask. Deletes what is inside the polygon.

Regards,
Eric

EricRice · Answer

Juliane,
One more way, if you don't want to take the time to build the water polygon or don't already have one...  You must have ArcGIS 10.0 minimum so you can access the Image Analysis Window.  There is a mask function button on the window that performs the type of masking your looking for.  i.e. Keep what is outside the mask.

See Using the Mask button on the Image Analysis window

Terminology differences:
Clip GP tool  - performs clip.  Keeps what is inside the polygon
Extract by Mask GP tool - peforms clip. Keeps what is inside the polygon
Clip Function (Image Analysis Window) - performs clip. Keeps what is inside the polygon
Mask Function (Image Analysis Window) - performs mask. Deletes what is inside the polygon.

Regards,
Eric