How do I 'label' an elevation raster to see individual cell values

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04-28-2010 03:56 AM
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New Contributor III
In some GIS packages it's possible to 'see' each raster value. Eg in SAGA GIS when you zoom in far enough each cell is labeled with its value, as attached.

Short of converting raster to polygon and labeling polygon layer, how do I get arcmap to perform this elementary task?

Thanks as ever to anyone willing to respond.
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New Contributor III
Thanks Bill. I think with Hawth's Tools it would be easy enough to create a regular grid of points, offset so they fall in the centre of each grid cell. I've often wondered how ArcGIS treats points that fall between cells, ie right on the border between two. By definition a point has no dimensions, so it can't be said to straddle either cell. But at the same time the raster surface covers the whole area, so I wonder how ArcGIS treats the no-mans-land in between cells. Perhaps they shift the point by an infinitely small amount so that it is then contained within a cell? Interesting thought...
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New Contributor III
Thanks Bill, that's interesting.

I suspect the 'point on boundary' issue has a lot to do with the units and projections you're using. Here in the UK everything tends to fall rather nicely onto a meter grid. Say you have a 5m raster and you take a bunch of GPS points (at 1m precision), there's a good chance many of those points will end in a 5 or a 0 and will hence straddle multiple cells, or rather straddle no cells depending on how you look at it.

Indeed, if those points are manually input at 10m precision then they're guaranteed to coincide with the corners of raster cells. I suspect it's more common than people think.

I am still unsure how ArcGIS treats rasters. The way it symbolises them makes you think any point in each cell acquires the value of that cell, but equally on my line of sight thread (http://forums.arcgis.com/threads/3458-Strange-results-from-line-of-sight-tool) it's evident that there's some interpolation going on!
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Regular Contributor III
Please feel free to check the Cell Tool sample out.

http://edndoc.esri.com/arcobjects/9.0/Samples/SpatialAnalyst/CellTool/CELLTOOL.htm

The Cell Tool toolbar provide tools to draw cell boundary, cell value, aspect and flow direction arrow as graphics.

Best Regards,
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New Contributor III
Very cool tool. Thanks for pointing it out. I wonder how many other cool samples are hiding out there? I should have a look through them
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