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Notes:

  1. For ArcGIS procedures see ET Solution Center
  2. All the examples are applicable to ET GeoWizards with small modifications.
  3. The TIN and Thiessen Polygons in ET GeoWizards are at least 100 times faster than these in EditTools
 

Create non overlapping buffers with attributes

1404ex10.jpg (3053 bytes)

1404ex11.jpg (12131 bytes)

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?

1404ex12.jpg (8038 bytes) Step 1. Create buffers from the points

Use: ET Geoprocessing - Buffer

Now we need to split somehow the merged buffered area

1404ex13.jpg (11582 bytes) 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)

 

1404ex15.jpg (10318 bytes) Step 3. Split the buffer polygon theme with the Thiessen polygon theme

Use:

  • ET EditTheme - select the buffer theme
  • Start editing the buffer theme
  • Click on Split with polygon button
  • Select the Thiessen polygon theme as a split theme
  • Stop editing the buffer theme

 

1404ex16.jpg (9870 bytes) Step4: Get the attributes from the source theme

Use:

  • ET EditTheme - select the buffer theme
  • Click Attributes from points
  • Select your source point theme as attribute source

If no overlapping buffers are present you can skip steps 2. and 3.

1404ex20.jpg (4288 bytes) 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

1404ex21.jpg (9328 bytes) Step 1. Create buffers from the points

Use: ET Geoprocessing - Buffer

1404ex22.jpg (9462 bytes) Step 2. Create Thiessen polygons from the polylines

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
  • use dissolve option with the attribute you want to transfer

NOTE: For best results create vertices in each polyline very close to the intersections

1404ex23.jpg (9457 bytes) Step 3. Split the buffer polygon theme with the Thiessen polygon theme

Use:

  • ET EditTheme - select the buffer theme
  • Start editing the buffer theme
  • Click on Split with polygon button
  • Select the Thiessen polygon theme as a split theme
  • Stop editing the buffer theme
1404ex25.jpg (9999 bytes) Step4: Get the attributes from the source theme

Use:

  • ET Geoprocessing - Attributes from polygon
  • Select the Thiessen polygon theme as a source
  • Select the center inside option

Create street center lines from cadastral polygons

For ArcGIS see the Create Centerlines function of ET GeoWizards

4032001howto01.jpg (17809 bytes) Source theme: - cadastral polygons

The goal: - to create street center lines

40320010howto02.jpg (11335 bytes) Step 1. - Dissolve cadastral units in a blocks. The gaps are road reserves.

Use:

  • Dissolve function on ET Polygon dialog
  • Local Dissolve function on Polygon Edit Tools dialog
40320010howto03.jpg (11434 bytes) 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

40320010howto04.jpg (21958 bytes) 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

40320010howto05.jpg (22066 bytes) 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

40320010howto06.jpg (9522 bytes) Step 6: Dissolve the Thiessen polygons using the unique attribute:

Use: Dissolve function on ET Polygon dialog

40320010howto07.jpg (14270 bytes) Step 7: Convert the polygons from the previous step to polylines:

Use:

  1. ET Convert - Polygon To Polyline
  2. ET Polyline - Clean:
    • Intersect
    • Remove duplicate lines

Step 8. Generalize the resulting polylines

Use: ET Polyline - G_D_S_F - Generalize - with an appropriate tolerance

Create distance themes

40320010howto11.jpg (5624 bytes) Source theme: - points, polylines or polygons

The goal: - to create continuos theme representing the distance from (to) the features of the source theme

40320010howto12.jpg (44650 bytes) 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).

40320010howto13.jpg (33436 bytes) 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.

40320010howto14.jpg (19156 bytes) 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

40320010howto15.jpg (17822 bytes) 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

40320010howto16.jpg (44459 bytes) Step 4: - Derive distance contours from the TIN created in the previous step

Use: ET Surface - 3D Analysis wit the TIN created

  1. Analyze ( No Slope, Aspect or Hillshade needed)
  2. Interpolate Contours

 

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