Raster to polygon conversion

[Lurker]

Hello all, just want to share and maybe little help here

I maka slope classification using ArcGIS, that result in raster format  :azn:

the real problem is to make it shapefile which is vector file (polygon)

Right now, from what I know, the only way to make smooth and good slope polygon from raster is by manually digitize it  :lipsrsealed:  which is really annoying if you face large area  :shocked:

I try to directly convert it via raster to polygon conversion, which lead to really bad polygon,  :cry:, polygon result from this conversion will have non smooth boundary (line follow the pixel of the raster that lead to zig zag lines)

I try to generalize and smooth it with cartography tool but only lead us to topology damaged polygon

any clue on this ?  I know that somehow there is a way to do this automatically, :cheesy:

[EmperoR]

hem, way to make line look smooth :

- Boundary Clean to smooth the boundaries

- Majority Filter with HALF option to smooth distribution of cells

- Filter to reduce anomalous cells

- Contour with a value to create a non-existent interim value (e.g. 2.5 with integer cell values)

[Cachanga]

You can use the Simplify Polygon Tool to get rid of the zickzack boundaries. Activate the "Resolve topological errors" function to avoid topological errors. Unfortunately the Smooth Polygon Tool doesn´t offer that funtion (yet?). The result is not perfect, but will be improved, and the file size will be much smaller because you get rid of many unnecessary points.

Hope that helps. Keep in touch, if you find a better solution.

Another option could be to ENVY Ex instead of ArcGIS. I got pretty good results with that.

[EmperoR]

can you explain to us how to use ENVI EX ?

[Lurker]

I try simplify polygon tool, and still, the result unacceptable, sometimes, the polygon look weird and funny, hem

never using ENVI EX before? please guide us

[rahmansunbeam]

OR you could give Golden Surfer a try! Its quite good for slope classification, hillshade or contour. Though I myself have many problems myself.  :sad:

[946]

You can also try Global_Mapper in 2 ways:

1. Load your resulted raster in GM and click on the layer to "Create Area Features from Equal Values in Selected Layer".

2. Open your elevation file in GM , triangulate if needed, and after export as "Elevation Grid Format" and choose "Float/Grid File".Mark the button with "Export Slope Values Insted of Elevations".

When you load this back to GM the sofware reads this information like elevation so you can generate contours from it. The values from the contours will be infact the slope values.

Hope it will help you!

[3dbu]

you can after convert to shape dissolve this data using GRIDCODe or another table atribuite, but too can use eliminate using low area like base for elimitate less than 1 hectares ...

[Lurker]

I will try the global mapper way, wish me luck,

actually in arcgis, I already have slope class raster, so everything is ready and done, except to make it into polygon format  :cheesy:

UPDATE

Okay, I've been able to manage it, although little bit rough :

1. Build slope class using DEM

2. Use admin step to smoothing the raster slope data

3. build contour based on the slope class

4. using query, you can manage to delete unnecessary line, based on the slope class, just maintain line that associated with slope class (limit value)

5. Edit topology of the contour, fix all undershoot or overshoot, we gonna make it polygon

6. convert it to polygon using "feature to polygon" tool

7. make query again, in this time, we gonna use attribute query and location query. first, your previous contour , make attribute query, to select the slope class, next, using location query, select the polygon based on the contour selection, now you can fill the slope class on to the polygon

8. finish, slope class piolygon with smooth line  :laugh:

[Cachanga]

Sorry, didn´t look in here for quite some time.

Good that you were able to get to a solution.

My proposal would have been to use ENVI EX supervised classification on the raster file. In the process of classification you can save a file as a vector/shp-file and choose the smoothing factor.

[pasfans01]

I have other method in order to create good slope polygon map

1. First, create slope map from DEM, reclassify it into desired slope class

2. Apply majority filter to the slope class map in order to remove patchy pixel

3. convert the majority filtered slope raster into vector polygon

4. eliminate the slivers polygon (polygon that have area below minimal mapping unit of certain scale) using eliminate tool in ArcGIS (data management tools>generalization>eliminate)

[3dbu]

I have other method in order to create good slope polygon map

1. First, create slope map from DEM, reclassify it into desired slope class

2. Apply majority filter to the slope class map in order to remove patchy pixel

3. convert the majority filtered slope raster into vector polygon

4. eliminate the slivers polygon (polygon that have area below minimal mapping unit of certain scale) using eliminate tool in ArcGIS (data management tools>generalization>eliminate)

i usually make the same methods and the output slope maps is very good.

regards

[Lurker]

great, thanx to all who share their knowledge here

+1 for pasfans01 and Cachanga

regards,