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ARCGIS raster view/export odd behavior

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#1
Martin Gamache

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I've just discovered some very weird behavior when displaying some raster data in arcmap. This particular dataset is a landcover GRID. I'm displaying it using unique values in the symbology properties, in theory this allows me to display each class in the color I want. Very useful for customizing a land cover map.

Here is the catch, when I zoom out of the display or export a layout as a raster image, a weird thing happens and a white border gets inserted around each contiguous group of pixels. These new pixels are set to whatever color is set as "all other values". If no color is set they are white. This is very frustrating behavior. It completely corrupts any raster export and also makes the maps very difficult to read when zoomed out

I'm not sure how and when this border effect gets created. It seems to be zoom level dependent as to when it starts happening on screen. I suspect it's some anti-aliasing bug or it has something to do with the number of classes perhaps having more than 32 classes is a problem. Does anyone know if there might be a setting hidden away somewhere to override this behavior. This only seems to happen with the "Unique Values" symbology. So if I can limit myself to 32 classes I guess I can work around it using the classified option. Still this is really annoying and I can't imagine this is the intended behaviour.

Charlie, Paul or Dave..can any of you clarify whether this is normal behavior or if this is being caused by my dataset?

I'm attaching some screenshots (small size png files so as to not cause any ethical crisis for derek) illustrating the problem.


mg

Attached File  normal.png   55.79KB   84 downloads Attached File  artifact.png   147.07KB   88 downloads

#2
Martin Gamache

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Digging around on the ESRI support site I've found a few things, none of which have solved the problem.

Here is a work around to the 32 class limit of the classified option: http://support.esri....l...how&d=19172

Using this approach the border problem I described in my first post does not show up. This leads me to believe there is something going on with the Unique Values option. I suspect it's some sort of generalization approach when you have a large number of classes. Presumably the goals would to make smaller areas more easily distinguishable as you zoom out. In fact I've noticed that large blocks of pixels of the same values are not effected until you are zoomed out very very far. I hope or would wish for a way of turning this annoying option off and why it gets exported that way is questionable IMO. A good example of what happens when the software tries to think for the operator ....it gets in the way & the results are undesirable.

Another potential suggestion was to rebuild the statistics using arc catalog which I've also tried and also managed to crash arc catalog every time so obviously that will not be a solution.

So I'm still looking for a solution. The classified option is rather difficult to work with.

#3
frax

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Martin,

You could, if you want to go the indexed/colormap route export it using a text color map (not sure how you do it inside ArcGIS gui, but it is very easy to do from workstation).

Another alternative, export it to a nominal color tiff, then it is easy to do the coloring in Photoshop (and one can save the colormap etc).
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#4
DaveB

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Martin,
Which Resampling option are you using in the Layer Properties > Display tab?
How many unique values are there in the data?
The AdvancedArcMapSettings.exe (found in your install location under ArcGIS\Utilities)has a setting on the Raster tab for Raster unique value limit. By default (looking at this in 9.2) it is set to 25. The text next to it says "Maximum number of classes (1-256)".
There is also a setting for maximum number of table entries (default = 65536), that may play into the crash trying to rebuild the statistics (I know very little about this part so I could be off-base here).
Dave Barnes
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#5
Martin Gamache

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Dave,

Interpolation is set to nearest neighbor and display quality to normal in the display properties.

In the advanced arc map settings I increased the unique value limit from 25 to 100 which I would of guess would make a difference but it did not. Same display issues.

There are 38 unique classes.

#6
DaveB

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hmm

One other question, do you have pyramids built for the raster?

I have played around with a landuse grid I have and don't see this problem, but it only has 7 unique values.
I'm not sure what else to say, unless you want to send me your grid to play with (if so, send me a message and I will give you the details).
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#7
Martin Gamache

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I don't see this problem with grids with small number of unique values either.

I did have pyramids built for it and I just tried deleting the .rrd file and that seems to fix the problem....

...thanks.

Did you suspect this was the problem?

hmm

One other question, do you have pyramids built for the raster?

I have played around with a landuse grid I have and don't see this problem, but it only has 7 unique values.
I'm not sure what else to say, unless you want to send me your grid to play with (if so, send me a message and I will give you the details).



#8
DaveB

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I don't see this problem with grids with small number of unique values either.

I did have pyramids built for it and I just tried deleting the .rrd file and that seems to fix the problem....

...thanks.

Did you suspect this was the problem?


Absolutely (actually, more of a lucky, slightly educated, trial and error guess) :D
Dave Barnes
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