Help with Simplify Line tool please!

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02-08-2012 04:33 AM
MitchelMoynihan
New Contributor
Hi Everyone,

I'm trying to run the Simplify Line tool on a 50m contour line set that won't process in the topo to raster tool as it says I have too many vertices. These can be removed by using the Simplify Line tool (thank you desktop help) however I'm stuck on what my "reference baseline" measurement should be in the Simplification Tolerance input section? Quoting the tool help it says "For BEND_SIMPLIFY algorithm, the tolerance you specify is the length of the reference bend baseline". Unfortunatley I have no idea what this means!!...Can anyone please point me in the right direction here?

On a side note, asides from running the Simplify Line tool is there any other way to reduce the amount of vertices in my contour shapefile? The contour file covers a large area and I have a feeling that the topo to raster tool may still crash even after the simplify line tool has ran. Is there anyway perhaps to increase the amount of points(vertices) the tool can process similar to increasing the max number of unique values a raster can handle?

Thanks,
Mitch.
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4 Replies
BogiBjornsson
Occasional Contributor
Howdy Mitch,

The way I have always understood the reference baseline is like in the image below:

[ATTACH=CONFIG]11856[/ATTACH]

So if you specify a distance that is shorter than that baseline all bends that have a shorter baseline than that will be smoothed out (vertices removed). Of course I'm sure the actual algorithm is more complex than that in reality but that is at least my general understanding of the concept.

As for the data set being to large to complete in one go through the topo to raster you can create a fishnet (using the fishnet tool) and cut your area up into tiles, processing each one at a time and then mosaic it together at the end. I would personally buffer each tile a bit as well so that when you mosaic you can use the option to calculate mean values on overlapping areas to get rid of edge effects in the final product.

Cheers!
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MitchelMoynihan
New Contributor
Hi Bogi,
Thanks for the reply.
Just to clarify on your understanding of the reference baseline, my input then should be the distance of my longest contour line?..meaning that any lines equal to or less than this length will be 'processed' and simplified? (I'm using the BEND_SIMPLIFY simplification algorithm).

Thanks,
Mitch.
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MitchelMoynihan
New Contributor
Hi Bogi,
Sorry, Having looked again at the image you provided I just realized that maybe it should be the distance/length of the whole study area that I should input given that it would then create a tolerance in which every contour line in the study area would be 'simplified' as they would fall within that tolerance. Am I way off the mark here or at least making some sense?!

Mitch.
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BogiBjornsson
Occasional Contributor
Hi Bogi,
Sorry, Having looked again at the image you provided I just realized that maybe it should be the distance/length of the whole study area that I should input given that it would then create a tolerance in which every contour line in the study area would be 'simplified' as they would fall within that tolerance. Am I way off the mark here or at least making some sense?!

Mitch.


All the lines in the data set will be simplified regardless of the baseline length, the baseline reference is only a measure of how much simplification occurs. If your reference value is small only small fluctuations (small bends) in your contours will be removed, if the reference value is large whole bends that should be in the data set and are real landscape will be lost.

My suggestion is to just have a look at your data and try to estimate what is the smallest bends you want removed and then try it on a copy of your data. Then try a larger value and/or a smaller value and note the difference so you get a better hang of how it works with your particular data set.

Cheers
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