The goal of benchmark hunting is to be able to log a recovery of the mark and an important aspect of a recovery log is benchmark photography.
The ["NGS"] says to take three photos if possible for a ["recovery report"]. Written primarily as requirements for survey agencies submitting geodetic marks for inclusion in the NGS database, but also pertaining to mark recovery reports of existing PIDs, the NGS has published the [http://www.ngs.noaa.gov/PROJECTS/INSTRUCTIONS/photos/Digital_Photo_Requirements.pdf Requirements For Digital Photographs Of Survey Control]. In this document, three types of photographs are discussed:
- close-up (taken vertically, with the disk mostly filling the view)
- Eye level (taken vertically, 5 - 6 feet distant from the mark)
- Horizontal view (taken horizontally, 10 to 30 feet distant from the mark)
Digital cameras usually require the use of a macro mode to be able to take a close-up photograph of the mark. Properly [:Equip-DiskCleaning:cleaning] the mark is a pre-requisite of a good close-up photograph so that all the stamping, including that on the rim of the mark, can be easily read.
The Eye level view is not often necessary, but in some cases the mark's situation is difficult to depict in the Horizontal view. An Eye level view will show how the mark is situated when you walk up to it. An example is a mark located in a complex area of a bridge ["abutment"].
It is important to note that the Horizontal view must have the survey marker in view. A photograph taken from the marker without it being in view is of no value to a recovery report. If possible, the Horizontal view should include one or more of the local landmarks used in the location description. Example: the ["datasheet"] says that the mark is 8 feet from power pole 687J, so take a picture so that both the power pole and the mark are in the picture. It is also important to note the compass direction (such as NW) you were facing when you took the Horizontal view photograph so that users of the photograph can properly orient themselves in their search for the mark.
Although the NGS requrements specify using temporary signs in the phographs, usually a photo editing program is used to insert such signs after the picture is taken. Be sure to take good notes about your photography so that you can do this accurately. Unless the mark is extremely obvious in the photograph, it is best to edit the photograph to insert a rectangle, circle, or triangle around the mark or insert an arrow to point directly on the edge of the mark. Red-green color blindness is the more common type of color blindness, so try to avoid using red and green markers, and use yellow, white, or blue instead, depending on which color will best contrast with the background.
When submitting photographs to the NGS, you must use the naming convention specified in the Requirements For Digital Photographs Of Survey Control referenced above.