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연구/X3D-Earth

Create Contour Lines with Point or Line Shapefiles

by fermi 2008. 5. 7.
http://little-yeti.com/gis_little_yeti/tuts/contour.htm

Create Contour Lines with Point or Line Shapefiles
The creation of contour lines as background data for archaeological maps is useful taks. Contour lines help other archaeologists and the general public visualize the terrain in which a site exists. The ability to visualize a site in its natural setting is a useful concept when explaining complex ideas such as site formation or human-induced changes in the physical environment.

ArcGIS makes generating contour lines from elevation data easy. The elevation data is typically in the form of points collected by either a total station, level, digital theodolite, or some other type of surveying instrument. This tutorial assumes that the elevation data (either as points or lines) already exists as a shapefile. However, if you only have a table of points that you still need to enter into the computer, please see the Converting a Coordinate Table into a Shapefile tutorial by clicking here.

In brief, generating contour lines requires two main steps. Using elevation data (in point and/or line form) to create a triangulated-irregular network (TIN) - which is simply a 3D model of the terrain, and the using this TIN to compute the actual contour lines. One of the neat functions of ArcGIS is that it allows the user to define what interval the contour lines are computed.

Programs used in this tutorial:
ArcCatalog
ArcMap

Extensions used in this tutorial:
3D Analyst
Spatial Analyst

The first step is to import the point or line shapefile into ArcMap. It doesn't matter how many shapefiles you have, or if you have a mix of point and line files. The program that creates the contours will merge data from numerous files. I used two files representing elevation points from consecutive years of mapping.



Once the shapefile has been imported, click the '3D Analyst' drop-down menu, select 'Create/Modify TIN' and click 'Create TIN From Featrues' which will open a dialogue box.



The dialogue box allows multiple files to be combined. The height source (elevation value) is computed from the Z value within each file.



Once the 'OK' button is clicked, the computer will computer the TIN and add it to ArcMap. Make sure you remember where you stored the TIN in case you need to use it again in the future.



The TIN in the above image can now provide the neccessary data for generating contour lines. The first step is to open the 'Spatial Analyst' drop-down menu and select 'Surface Analysis' and the click on 'Contour'



The contour dialogue box will open, it should automatically select the TIN created previously (named 'tin' in this example). You can set the contour interval in this dialogue. IMPORTANT: the interval is a product of the measuring system used to collect the elevation data, in other words, if you took measurements in meters, than one interval will generate one meter contour lines.



Select where you want to store the output shapefile (features) and then click 'OK', and ArcGIS will generate your contour lines.



There you have it, you have created contour lines for your site!