Importing Contours from PC ARC/INFO

1) In PC ARC/INFO, use ARCSHAPE to export the contour data.

Macro example:

   ARCSHAPE topo topo line
2) In Idrisi, use SHAPEIDR to convert the shapefile to an Idrisi vector file.

WARNING: Do not use the macro version of SHAPEIDR as there seems to be a serious bug that wipes out the attributes.

3) Use INITIAL to create a base image for the area (the vector's document file contains min and max XY information).

Macro Example:

   INITIAL x topo 1 1 0 2 815 481 plane ft 11540 19690 9970 14780 1.0 ft
4) Use LINERAS to add line values to the image.

Macro Example:

   LINERAS x topo topo
5) In DATABASE WORKSHOP, open the vector attribute table and assign the elevation field values to the image (the feature definition field should be IDR_ID).

Because a 2-byte integer field is required for assigning values to an integer image, it may be necessary to add an integer field to the table and populate it from the elevation field.

SQL Example:

   UPDATE topo
   SET [elev2] = [elev]
6) Use INTERCON to interpolate the surface elevations from the contours. To estimate corner values, you can use the cursor query tool on the display created by the ASSIGN operation in step 5.

Macro Example:

   INTERCON x topo2 dem 0 1628 1466 1402 1417
7) Apply FILTER as desired to smooth out any angular effects.

Macro Example:

   FILTER x dem dem2 1
8) [Optional] Crop the DEM to the project boundary.

If the project area is irregularly shaped, create a boundary polygon in PC ARC/INFO. The polygon should be completely inside the contours so that edge effects may be clipped out. Convert the coverage to a shapefile and import it into Idrisi.

Use INITIAL to create an image from the DEM with a value of 0. Then use POLYRAS to add the vector file data to the image. Because the polygon's value (IDR_ID) is set to 1 and the INITIAL image is set to 0, the result is a mask that may be multiplied against the DEM image to zero out the outlying areas.

MACRO Example:

   INITIAL x demv 3 1 0 1 dem2 unspecified
   POLYRAS x clip demv
   OVERLAY x 3 dem2 demv demov
Finally, before performing any surface analysis, you will want to do the following in DOCUMENT: a) make sure that the value units are set appropriately, and b) set the flag value to "0" and the flag definition to "background".

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