Aspect raster every 30' ?

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01-02-2017 08:48 AM
GalaNuñez
New Contributor II

Hello,

I need to classify my Aspect raster every 0.5 degrees (30'). It's an Aspect raster of euclidean distance from a single point. The INT tool only provided me with 360 degree values, that is every 1º but I require more precision.

How can this be done?

Thank you

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11 Replies
DanPatterson_Retired
MVP Esteemed Contributor

This is how aspect is calculated in ArcGIS Aspect—Help | ArcGIS Desktop  and How Aspect works—Help | ArcGIS Desktop 

If you don't want to use a finite difference method, could you elaborate on what it is you are going to use?

XanderBakker
Esri Esteemed Contributor

You could do this: Int(Aspect * 2). However, just like Dan_Patterson‌ I am very curious to know why you want to obtain 720 classes...

GalaNuñez
New Contributor II

Int(Aspect * 2)

Do I use the raster calculator for this? 

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DarrenWiens2
MVP Honored Contributor

Yes, this goes in Raster Calculator, although I think you want the following expression that will round to the nearest 0.5 (Int truncates, it doesn't round):

Int("aspect"*2+0.5)/2.0
GalaNuñez
New Contributor II

I'll try this, thank you.

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GalaNuñez
New Contributor II

Oh, it doesn't work. Zonal Statistics as Table won't accept the raster.... 

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DanPatterson_Retired
MVP Esteemed Contributor

read this carefully ... in the fine print, Zonal Statistics as Table—Help | ArcGIS Desktop only works when the selecting raster has a table... you are going to have to be specific on what you did.  And you should not be using the defaults since you have to go into the Environments tab and specifically specify a cell size and extent when you are creating your zone raster

GalaNuñez
New Contributor II

Thanks. I am using the Zonal Statistic as Table tool to obtain a table with all the maximum values associated to 360 degrees. I then plot the results in excel and create a simple linear graph.   

-I reclassified the resulting raster using the formula and obtained 720 classes. This raster was accepted by the Zonal Statistics as Table tool. It seems to be working. Still, I am not sure this is going to take me to the result I am looking for.

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GalaNuñez
New Contributor II

I'm trying to create a table that relates elevation in a DEM with viewing angles from a single point. I need a realistic graph of the terrain in the horizon, but as it is now, with only 360 degrees, many details are lost. I'm using Zonal Statistics as Table tool to do this. Can you help me? 

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