Raster Tools affecting outlines after Polygon to Raster Conversion

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06-15-2021 03:06 PM
MatthewDembo
New Contributor

Images from ArcGIS Desktop, but Online showing same thing.  I am a student doing my best to build a raster from scratch.  I have chosen a study area drawn as a polygon, that I then want to convert into a raster because I have collected data on it using a grid system of letters and numbers.  The process has been draw a polygon, then modify the polygon with the divide tool.  This appears to work okay (cells not aligned, but it's fine for this purpose.) with the polygon to raster tool, but every subsequent raster tool is affecting only the outline between the original cells.  Any suggestions on what to try here??

 

Drawn Polygon, after divide tool used:

MatthewDembo_1-1623794587331.png

 

 

Result of Polygon to Raster (Elevation):

MatthewDembo_0-1623794543924.png

 

Result of Slope Tool, using raster above.  Looking at the lines in-between cells, those are where the tool output is being generated...

MatthewDembo_2-1623794644197.png

 

Result of Hillshade Tool, using elev raster input:

MatthewDembo_4-1623794687380.png

 

3 Replies
JansenLyons
Occasional Contributor III

Hi @MatthewDembo this could happen if all the cells are seen as the same value and only the outline is seen as the difference. One way to get around this is to remove the outline from the raster and let the changes in the cells' values dictate the raster changes based on value such as in the hillshade. Save the outline however and overlay it as a new layer and see if that solves it, I've run similar workflows and found that to be how I solved it. What version of software are you using if I may ask? Not too sure if this would matter but it's good practice to just run down the list of possible problems and narrow down further and further. If nothing else it will help build practice knowing the workflow and software.

Hope this helps, have a great week!

Jansen Lyons - Records and GIS Section - Public Works - City of Rio Rancho, NM
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MatthewDembo
New Contributor

Hey Jansen, thanks so much.  I am in 2.8.0

I assume you mean remove the outline as in change the Symbology to have no outline?  I changed the initial polygon to have no outline symbology and then reran the tools.  The outputs seem to be the same (photos at end).  The difference in elevations are relatively small - about 8 feet over the course of the study area, but it seems like the tool is trying to show the differences.  I'll keep trying on my end but let me know if that's what you were suggesting

Polygon, outlines removed (symbology)

MatthewDembo_0-1623942835348.png

 

 

Polygon to Raster Tool, using elevation values from polygon with no outline

MatthewDembo_1-1623942883843.png

 

Slope tool (% rise) on previous elevation raster

MatthewDembo_2-1623942932226.png


Hillshade tool output

MatthewDembo_3-1623942975294.png

 

 

JansenLyons
Occasional Contributor III

Hi @MatthewDembo , yes, that is what I meant. It doesn't look like it had the same outcome that I did, but it may just be the small size of your raster. The goal of isolating the pixels/polygon divisions to inches instead of feet or whichever unit you are going off of per change. That way it's not merely the whole number but covers a great change. When I did the workflow it helped free up processing power enough to generate a proper hillshade or Slope tool results when you remove any extraneous layer or action for AGOL/ArcMAP to render. You may want to try and increase the resolution or enlarge your work area if you are looking for hillshade or slope specifically. It looks like the polygon to raster tool is working well, perhaps divide the polygon further and build out from there? Hope this helps get closer to your answer. One topic that is always fun and a great start is to look into how Mars rasters or DEMs are built. I'll leave a link below so you can see what I mean.

https://www.esri.com/arcgis-blog/products/js-api-arcgis/3d-gis/explore-mars-with-gis/ 

Best,

Jansen Lyons - Records and GIS Section - Public Works - City of Rio Rancho, NM
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