Supporting Documents:
The City maintains a grid of Survey Control Monuments (Monuments Vicinity Map) which locally serves as a surveying reference points. The monuments aid in delineating public and private properties, surveys, subdivisions, construction projects, and especially projects sensitive to accurate vertical elevations such as efforts related to FEMA floodplain, etc. Aerial flyovers also utilize the monuments to aid in orthorectifying, or horizontally and vertically adjusting, aerials and subsequent topographic data as these products are converted to GIS layers and data in GIS to more accurately reflect actual real earth surface locations.
In 1994, the City had 86 Survey Control Monuments (1994 - in OLD Datums) constructed. However, since that time 20 monuments have been damaged or removed in construction or adjacent activity. Additionally these original monuments were provided in datums that are becoming outdated (horizontal: NAD-27 and NAD-83, and vertical: NGVD-29).
In conjunction with the 2005 aerial fly-over contract with Kucera International, Inc., GeoMetrics GPS, Inc. performed a Photogrammetric Control Survey (2005) to provide additional, updated horizontal and vertical control for mapping in the same noted coordinate system and datum.
After the City hosted a roundtable discussion with local surveying community in 2009, the City proceeded to contract with CDS/Muery Services in 2010 to establish 11 new monuments to supplement the loss of monuments and to update the monument grid to more current survey datums (horizontal: NAD-83 (CORS Adjustment) and vertical: NAVD-88). Additionally, the new monuments utilize a more stable and durable construction method of deep rod survey monuments driven to refusal, instead of the previous common discs simply set in 6 inch diameter 3 feet deep concrete pier. The complete, detailed Survey Report (2010) describing survey methods and procedures as well as raw data is available. These 11 deep rod monuments constructed in 2010 are the "primary" elevation control for College Station.
In 2011, the City contracted with Joe Orr, Inc. to update the datums and re-survey the original remaining 1994 monuments to match the new deep rod monuments. The Survey Control Monuments (2010 and 1994 - in NEW Datums) and Joe Orr's associated Survey Report (2011) with metadata is available. Note that 2012 FEMA Map Modernization project (Series "E") is complete which similarly updates and coordinates to reference vertical datum to NAVD-88 (CORS Adjustment) as well. An effort is now underway to install small pipe bollards to further protect the monuments for long term use. These remaining 1994 monuments with updated elevations conducted in 2011 are "secondary" elevation control.
In 2012, the City contracted again with Joe Orr, Inc. to locate the remaining elevation reference marks (RMs) identified on the Series "C" and "D" FEMA Flood Insurance Rate Maps (FIRMs), and to determine respective NAVD-88 elevations. This Survey Report (2012) confirms which monuments remain and lists elevations for the RMs in the Flood Insurance Study which were originally based on the NGVD-29 datum, where the Series "E" FIRMs are referenced to the NAVD-88. These historical FEMA benchmarks and reference marks with updated elevations surveyed in 2012 are "supplementary" elevation control.
The National Geodetic Survey (NGS) has created the National Spatial Reference System (NSRS) which is the official reference system of the federal government that allows a user to determine geodetic coordinates including latitude, longitude, height, etc. NGS develops and determine multiple region-specific datums. The current local datums are NAVD-88 for Vertical, and NAD-83 (CORS Adjustment) for Horizontal. NGS has numerous benchmarks across the nation and data on these monuments can be retrieved from the following link on National Geodetic Survey Registered Benchmarks. Specifically, benchmarks BM0026, BM0028, BM0032, and BM0033 are the remaining NGS benchmarks in College Station city limits, all of which were recently surveyed and included with the Survey Report (2012) with updated datums as referenced.
LiDAR
In conjunction with College Station's 2011 aerial fly-over contract with Kucera International, Inc., horizontal and vertical control for mapping was performed by means of LiDAR. College Station's LiDAR data is comprised of tens of thousands of georeferenced points with elevations that have many uses for engineers, GIS users, etc. Texas Natural Resources Information System (TNRIS) prepared Final Data Inspection Report - Brazos Orthoimagery (2011). Kucera provided the raw LiDAR LAS Elevation Data Point Files (2011). Click the link for '2011 LiDAR.zip' and extract the compressed files for use. For additional information using the site, please view and read the 'readme.txt' file.
LiDAR (also written LIDAR or Lidar - excerpts from Wikipedia) is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light. Downward-looking lidar instruments fitted to aircraft and satellites are used for surveying and mapping. The term lidar comes from combining the words light and radar. Lidar is popularly known as a technology used to make high resolution maps - in this case, specifically contour mapping. Lidar uses ultraviolet, visible, or near infrared light to image objects and can be used with a wide range of targets, including non-metallic objects, rocks, rain, etc. A narrow laser beam can be used to map physical features with very high resolution. Lidar was developed in the early 1960s, shortly after the invention of the laser, and combined laser's focused imaging with radar's ability to calculate distances by measuring the time for the signal to return. The general public became aware of the accuracy and usefulness of lidar systems in 1971 during the Apollo 15 mission, when astronauts used a laser altimeter to map the surface of the moon.
Additional LiDAR data for other areas across the state is available directly from Texas Natural Resources Information System (TNRIS) through their Services Order Form: https://tnris.org, or they can call the TNRIS main line at 512.463.8337.