If you've ever wanted a big shape file or Google Earth KML of NGS benchmarks, here's a method:
1. Whip up a python script to fetch the data sheet shape files for all 50
states and territories. This will spare you manually submitting 50+ individual
requests. Here's mine:
http://www.pseentertainmentcorp.com/python/DataSheet_Shape_Fetch.pyWhen completed you'll have 50+ zip files containing all the benchmarks in the NGS database.
2. Next merge them into one big shape using ArcMap (or your favorite GIS application). This file has about 760,000 points!
3. Next filter on A, B, and 1st order monuments. These are very high quality, geodetic grade benchmarks. Such monuments are suitable for high accuracy GPS observations. Of course, you can filter on any criteria you'd like...
4. Use the Export to KML ArcGIS extension to create a big KML. You can get this at
http://arcscripts.esri.com/details.asp?dbid=142735. Open this file in Google Earth and fine tune the display settings to your needs then 'save as'.
6. As a added bonus, the URL to fetch the actual datasheet is present in the KML for each point. When viewing these points, take the data (i.e. Lat/Lon) inside the shapefiles/KML with a grain of salt - only the DATASHEET is the truth!
Here's a link to a completed KML with about 50,000 high quality NGS benchmarks.
http://www.pseentertainmentcorp.com/python/Good_NGS_Points_Dec2007.kmzEnjoy!
Webmaster
