No data areas will not be used in calculations and statistics. You can use the "SetNull()" function in Raster Calculator to set areas that should be masked to NoData. Result was a raster with vegetation height data and no-data, which is what I want. This is often because the NoData value was not specified in a way that ArcMap understands. First I calculated a DEM for vegetation height and a binary image (0,1) for cover. Sometimes when you bring a raster into ArcGIS you'll see that the range of values is crazy and it's hard to see your raster data. The image that I have problem with it is the outcome of linear spectral analysis of ENVI software. What we have done is masked out everything but the area that we are interested in (habitat for adult brown shrimp) and colored it red.Įsri refers to pixels that are "masked out" as "NoData" (properties and symbology) and sometimes as "NULL" values (in raster calculator). The example data used in this tutorial are. Most of the white area is land and is also in correct and should be masked out. In this video tutorial, we show you how to do a simple DoD Analysis in ArcGIS 10 just using the rater calculator. The raster in the background represents the entire raster and you can see there are black pixels in the upper left that just contain 0s and should definitely be "masked out". The raster below contains bathymetry (depth of the sea bed below the water level) for the Gulf of Mexico (in black and white) and the habitat for adult brown shrimp (in red). Rasters are always rectangular but quite often we want to "mask" part of the raster because the area of interest, or the area that actually have read data for, is smaller than the size of the raster. This meant I had to "define" the spatial reference to the correct one. I had to spend some time with the raster trying different spatial references and discovered that is was an incorrect spatial reference. The challenge with rasters is that this could be because of an incorrect spatial reference or incorrect georeferencing. the data appeared closer to the Bahamas than the Gulf of Mexico! Below is an image of a raster with elevation data along the coast of the Gulf of Mexico that I downloaded from a government agency. If the spatial reference is incorrect, the raster will not appear where it should. ArcGIS will alert you if the spatial reference is missing and you can check the spatial reference in "Properties". The signs that a raster is missing a spatial reference or that the spatial reference is incorrect is the same as for shapefiles. In addition, a raster is just a rectangular grid of pixels so it must have additional information that "pins" that data to the earth (georeference it). Lack of a Spatial Referenceīecause of the large number of file formats available, fixing problems with spatial references with rasters can be more tricky than with vector data. There are a number of problems we can into with raster data.
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