NGS Benchmarks on ESU campus
Geospatial Analysis Exercise
James S. Aber
The U.S. Coast and Geodetic Survey is now known as the National Geodetic Survey—see NGS. During our GPS demonstration on campus, we recently visited two survey benchmarks set in concrete. Both benchmarks are dated 1956, a time when many benchmarks were placed in this vicinity. Previous measurements were conducted at these benchmarks using two identical Garmin Rino 110 GPS units set for NAD 83 as well as a high-precision Archer GPS unit.
||Benchmark outside the ESU White Library building. This benchmark was placed by the U.S. Coast and Geodetic Survey in 1956 and is marked "Emporia State" No. 1. This name is peculiar, because in the 1950s the institution was called Kansas State Teachers College. The current name was adopted in 1977—see about ESU. Another curious fact is that the arrow on the benchmark points to the southwest. Photo © J.S. Aber.
||Site 1: Southeast of the library, beside Kellogg Circle, named Emporia State No. 1. High-precision Archer GPS unit is accurate to the nearest meter.|
UTM: zone 14, 4255365 N and 746160 E (N & E values given in meters).
Lat/long: 38° 24' 45.52" N and 96° 10' 50.37" W (degrees, minutes, decimal seconds).
||Site 2: South of the library, close to 12th Avenue, named Emporia State. Two Garmin GPS units are accurate to within a few meters.|
UTM: zone 14, 4255346 N and 746147 E (N & E values given in meters).
Lat/long: 38° 24.746' N and 96° 10.850' W (degrees and decimal minutes).
||Site 1 benchmark was photographed using a GPS-equiped Nikon camera with a built-in world map. The map is highly detailed including pedestrian walkways on campus. Camera lat/long values are N 38° 24' 45.56" and W 96° 10' 50.31". The GPS symbol (yellow circle) is located in exactly the correct position, which provides a high degree of confidence for the benchmark location. |
||Benchmark site 2 map shows the correct position (yellow circle) next to 12th Avenue. Camera lat/long values are N 38° 24' 44.99" and W 96° 10' 51.61".
Your task is to compare these past values collected using handheld GPS units with the values we collected during our class excursion as well as the official values recorded by the NGS. In order to compare UTM and latitude-longitude values, online conversion programs are available.
First enter lat/long GPS readings taken during the excursion for the first benchmark in degrees/minutes/seconds into the West Virgina converter (use values above for site 1). Note: enter latitude as positive and longitude as negative values. Click "convert" and a map will display. Zoom in to the street level.
Clearly the converted UTM values displayed at the West Virgina site are incorrect. This site is set up for UTM zone 17, which includes West Virginia, as the default zone. Change the UTM zone to 14 and convert the lat/long values again.
- 1. Does the location marked on the map appear to correspond with the actual position of the benchmark?
- 2. What values are given for decimal degrees (at bottom)? Why is one positive and the other negative?
- 3. Do the converted UTM values given at this site correspond with those we collected at the benchmark?
Now go to the NGS site, specifically to look up the datasheet for the ESU benchmark. Click on the "Datasheets" button, than click on the "USGS Quad" link. Enter the quad name = "emporia" and click the submit button. Three USGS quadrangles include Emporia in the name, one in Virginia and two in Kansas. Highlight the Emporia, KS entry (first line), and click the submit button.
4. What happened to the UTM values; do they now correspond with our GPS readings?
- 5. Based on UTM values, approximately how far apart are the two Emporia State benchmark?
You should now see a page titled Station List Results for: EMPORIA. There are several dozen NGS benchmarks for the Emporia quadrangle arranged alphabetically by name. Find the Emporia State entry, and highlight the line. Notice that latitude and longitude are given in degrees, minutes and decimal seconds, but the number is run together which makes it hard to read. For example:
N382444.65989 represents 38° 24' 44.65989" N latitude.
Now click on "Get Datasheets" to obtain more detailed information about the site. Note: this may take a couple minutes; if you get an error message, go back, hit the reset button, and try again. Sometimes the NGS site seems to be "down" so you might have to try later.
- 6. What are the position values listed under Current Survey Control for the Emporia State benchmark? Also note the NAD 27 values for Superseded survey control.
- 7. How do these values compare with those we collected with GPS units on the campus excursion? Hint: convert NGS lat/long values into UTM for easier comparison using the Montana site.
- 8. Assume the averaged GPS values (taken from multiple readings) and the plots of the benchmarks shown on the maps are within 10 feet (3 m) of true location (NAD83). Which of the two Emporia State benchmarks corresponds closest to the official NGS benchmark location?
- 9. Also consider the curious north arrow on the benchmark (site 1). Based on all information, suggest what may have happened to this benchmark.
Now turn your attention to the Allen benchmark located 2˝ miles north of the city of Allen directly north of Emporia in Lyon County, Kansas. This benchmark is situated on the third principal parallel, an E-W line along which townships are slighly offset to accommodate the curvature of the Earth. This benchmark also happens to rest beside the historic Santa Fe Trail route as it enters the Flint Hills physiographic region.
||Left: witness post marks the position of the benchmark on the ground. Right: close-up view of the Allen benchmark. Although concrete obscures the edge, this is another U.S. Coast and Geodetic Survey marker placed in 1956. Photos © J.S. Aber.
||Left: sign marking preserved ruts of the Santa Fe Trail. Right: Old Allen site on the Santa Fe Trail. Allen was relocated 2˝ miles to the south when the Missouri-Pacific Railroad was built across northern Lyon County in 1886. Photos © J.S. Aber.
While the Allen NGS Data Sheet is on screen, right click on the display window and Save Page As using the name "allen_datasheet." This will create a small html file; be sure to save this in your student working folder.
- 10. Once again, go to the NGS site, find the datasheet for the Allen quadrangle, and identify this benchmark by its name or identification number (PID - JF1343). What are the lat/long and UTM coordinates for this benchmark? What is its elevation?
- 11. Finally compare the Emporia State and Allen NGS benchmark values (NAD 83). Notice that the UTM easting values are nearly the same. What is the north-south distance between these two benchmarks in km and miles?
- Written answers (1-11).
- allen_datasheet.html file.
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ES 351 © J.S. Aber (2016).