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Example1: Source theme: Point
theme The goal: to create non overlapping buffers around the points that will carry point's attributes The Buffer Wizard (standard with ArcView 3.1 and above) has options to merge or not the buffers, but do not allow the point attributes to be carried over to the resulting polygons. There are couple of scripts available on Arc Scripts page that will allow transferring the points attribute to the created buffers, but the requirements are to use non merged buffers. What will happen if the buffer distance is bigger than the distance between the points? The picture on the left illustrates it very well. - Plenty of overlapping circles that do not allow any analysis to be performed Edit Tools does not tolerate overlapping polygon features. Its buffer function will automatically merge the buffers that share common area. Then how to create buffers from the points in this example and attach the point's attributes to the buffers? |
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Step 1. Create buffers from the points Use: ET Geoprocessing - Buffer Now we need to split somehow the merged buffered area |
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Step 2. Create Thiessen polygons from the points Use: ET Miscellaneous - Thiessen Polygons (use buffered Convex Hull option with buffer distance bigger than the buffer distance used in the buffer procedure in Step 1)
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Step 3. Split the buffer polygon theme with the
Thiessen polygon theme Use:
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Step4: Get the attributes from the source theme Use:
If no overlapping buffers are present you can skip steps 2. and 3. |
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Example2: Source theme:
Polyline theme The goal: to create non overlapping buffers around the polylines that will carry polyline's attributes In this case the overlaps are unavoidable. Read the notes about buffering from the previous example |
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Step 1. Create buffers from the points Use: ET Geoprocessing - Buffer |
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Step 2. Create Thiessen polygons from the
polylines Use: ET Miscellaneous - Thiessen Polygons
NOTE: For best results create vertices in each polyline very close to the intersections |
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Step 3. Split the buffer polygon theme with the
Thiessen polygon theme Use:
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Step4: Get the attributes from the source theme Use:
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Create street center lines from cadastral polygons
For ArcGIS see the Create Centerlines function of ET GeoWizards
Source theme: - cadastral polygons The goal: - to create street center lines |
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Step 1. - Dissolve cadastral units in a blocks.
The gaps are road reserves. Use:
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Step 2: - Convert dissolved polygons to
polylines. Since the polygons do not have common boundaries no additional cleaning is
necessary Use: ET Convert - Polygon To Polyline Step 3: - Dencify the resulting polylines. The distance between the vertices should be less than the road reserve width Use: ET Polyline - G_D_S_F - Dencify - with an appropriate tolerance |
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Step 4: - Create Thiessen polygons from
resulting polyline theme Use: ET Miscellaneous - Thiessen Polygons Note: This is the most time consuming part of the process - can be run overnight |
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Step 5: - Get the attributes from the block
polygons (the result from step 1) Use: ET Geoprocessing - Attr. From Polygons with intersect option. Only one attribute is needed - unique identifier of each block polygon |
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Step 6: Dissolve the Thiessen polygons using the
unique attribute: Use: Dissolve function on ET Polygon dialog |
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Step 7: Convert the polygons from the previous
step to polylines: Use:
Step 8. Generalize the resulting polylines Use: ET Polyline - G_D_S_F - Generalize - with an appropriate tolerance |
Source theme: - points, polylines or polygons The goal: - to create continuos theme representing the distance from (to) the features of the source theme |
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Step 1: - create a point grid theme Use: ET Miscellaneous - Point Grid The triangle option will give best results if you want to derive distance contours Select an appropriate grid size (distance between points and grid extent). |
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Step 3: - Calculate the distance from the grid
points to the features of the source theme. Use: ET Geoprocessing - Point Distance If you are happy with the representation this might be the result. If not - go on. |
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Step 4: Optional - Create Thiessen polygons from
the grid point theme. And classify them with the distance field. Use: ET Miscellaneous - Thiessen Polygons Note: The Thiessen Polygons procedure is time consuming |
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Step 4: Create 3D TIN from the grid points. Use
the distance field as an elevation field Use: ET Surface - Build TIN with the 3D option
Note: The CreateTIN procedure is time consuming |
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Step 4: - Derive distance contours from the TIN
created in the previous step Use: ET Surface - 3D Analysis wit the TIN created
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