The goal of benchmark hunting is to be able to log a recovery report of the mark and an important aspect of a recovery report 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 Requirements For Digital Photographs Of Survey Control. In this document, three types of photographs are discussed. The 1st and 3rd are the most important for recoveries:

  1. close-up (taken vertically, with the disk mostly filling the view)
  2. Eye level (taken vertically, 5 - 6 feet distant from the mark)
  3. 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 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. Look at your picture after you've taken it to make sure that you can see in the photo where the mark is in the image. If it is not obvious, re-take the picture with some sort of marker in the view so you can find where to insert an arrow in the view when you get home.

Although the NGS requirements specify using temporary signs in the photographs, 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.

There are many digital photograph editors available, many of which come with a digital camera. The Microsoft Paint program, included with Windows can also be used to make labels and arrows. Here are steps to use using Microsoft Paint to do the photo editing:

  1. Start the Paint program (Start, Programs, Accessories, Paint) and open your Horizontal view photo file
  2. click on the letter A in the Tool Box
  3. mark out a space for the label in the photograph
  4. use the two red, yellow, green, and blue icons to select whether you want a opaque or transparent background (transparent is preferable for indicating the position of a mark, while opaque is preferable for labeling)
  5. select the foreground (and background if you're using a solid background) colors with the color chart at the bottom of the window
  6. if the text toolbar is not showing, right-click in the text box to select it to show
  7. in the text toolbar, choose the "Wingdings 3" font and select a fairly large font size like 48
  8. for arrow keys, select the arrow direction from among the "f" through "h" keys
  9. use transparent mode to surround the image of the station with these choices: for a triangle, use the "r" key, for a square, use "Wingdings 2" font and a "5" key, or "Webdings" font and a "c" key
  10. after you finish typing the symbol, move your cursor to the edge of your text box until it becomes a solid white type of arrow, then hold down the mouse button to move the symbol to point onto the benchmark
  11. when you have finished, click on the picture.
  12. Another way to make a square or rectangle: make sure you've selected the transparent mode, then select either an ellipse or a rectangle in the tool box and form it around the geodetic mark's image.
  13. For identification labeling, select a regular, preferably sans-serif, font such as Arial, and select opaque mode with a white background. Place the label in a part of the photograph that provides the least visual information about finding the mark.

When submitting photographs to the NGS, you must use the naming convention specified in the Requirements For Digital Photographs Of Survey Control referenced above.

photography (last edited 2009-03-21 21:03:18 by localhost)