Clipping orthophotos

Brian Wilson 16:04, 16 Sep 2004 (PDT)

Those little suggestions -- it would be cool to have the area outside your park boundary be black and white and the area of interest be in color...

It took me a week to figure out how to do this so I best write it down for next time.

I went through all the steps to learn how to do it wrong in Arc/Info before figuring out the best way in ArcMap. Now I can even do it at home. (I have Spatial Analyst at home but not Arc/Info)

I will add some photos here someday.

My first concept was to create a full color photo in the center of my map by clipping the orthophoto to match the park boundary. To do this, I had to convert the 4 photos in TIFF format into GRID format, then merge them together. The tricky part was realizing that the GRID format splits each photo into 3 bands, and the ESRI tools will only process one band at a time. If you decide to go this route, after processing each band separately you can glue them back together using "MAKESTACK" in either Spatial Analyst or Arc Workstation.

It's a mistake though. When I converted the TIFF to GRID, the IMAGEGRID command gave me 'sharpened' images. It altered the color saturation such that the finished map was ugly. Perhaps there is a way to control this but I took another route.

Instead of clipping the edges off the color orthos, I punched a hole through the b&w image and put the b&w image on top. The result is the same -- b&w surrounding a color center, but I did not have to process as much data (just one band for b&w photos) and did not have to modify the more attractive original color TIFF photos.

To get more information on the relevant ESRI tools, use the search box at http://www.esri.com/ to look for "Practical Guidance for Raster Graphics" and "Mosaic multiband images using ArcGIS and Spatial Analyst".