topic Re: Aspect raster every 30' ? in Geoprocessing Questions

Aspect raster every 30' ?

GalaNuñez — Mon, 02 Jan 2017 16:48:55 GMT

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

Re: Aspect raster every 30' ?

DanPatterson_Retired — Mon, 02 Jan 2017 17:13:37 GMT

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?

Re: Aspect raster every 30' ?

XanderBakker — Mon, 02 Jan 2017 17:26:23 GMT

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...

Re: Aspect raster every 30' ?

GalaNuñez — Tue, 03 Jan 2017 20:56:05 GMT

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?

Re: Aspect raster every 30' ?

GalaNuñez — Tue, 03 Jan 2017 21:00:40 GMT

Int(Aspect * 2)

Do I use the raster calculator for this?

Re: Aspect raster every 30' ?

DanPatterson_Retired — Tue, 03 Jan 2017 21:09:31 GMT

why not take the outer boundary of a viewshed, convert it to a polyline and use it to extract the elevation profile?

Re: Aspect raster every 30' ?

DarrenWiens2 — Tue, 03 Jan 2017 21:11:26 GMT

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

Re: Aspect raster every 30' ?

GalaNuñez — Wed, 04 Jan 2017 00:50:31 GMT

I'll try this, thank you.

Re: Aspect raster every 30' ?

GalaNuñez — Wed, 04 Jan 2017 01:02:08 GMT

Thanks for this suggestion. I tried something like this at some point but had so much trouble with erasing all the 'non-visible's from the 'visible's in the viewshed raster, I gave up. Also, the final graph needs to relate degrees with elevation points in meters.

I'm going to put up another thread explaining what I'm trying to work out. Thank you all for your help.

Re: Aspect raster every 30' ?

GalaNuñez — Thu, 05 Jan 2017 02:37:38 GMT

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

Re: Aspect raster every 30' ?

DanPatterson_Retired — Thu, 05 Jan 2017 03:10:14 GMT

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

Re: Aspect raster every 30' ?

GalaNuñez — Fri, 06 Jan 2017 23:11:23 GMT

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.