Photogrammetry – A Field Guide

PhotoSimulations

Field Data

When gathering field data to be used in PhotoSims there are a few important guidelines to follow that will help produce quality cost effective deliverables.  One of the most important aspects is the photograph of the location/structure to be used. Let’s look at the criteria for a good shot below;

Framing the Shot

Photo simulations are created to show the addition of new Equipment, Structures or Antennas and occasionally the addition of ground-based equipment. It is necessary to keep in mind the possible inclusion of these pieces to the photograph. Below, an example image of a good shot.

  1. Ample Vertical Space
  2. Ample Horizontal Space
  3. Minimal Foreground Space

Keep in mind that it is better to get too much horizontal, vertical, and foreground spacing.

As an example; A project’s design and scope may be altered later to include ground equipment in an unknown location. Providing ample room may remove the need to revisit the project location for new photography.

The photo can be sized later to remove an excess of an area from the photo simulation.


Points to Consider

  • Be aware of your surroundings and wear a reflective safety vest while in the field.
  • Be diligent about keeping the public / license plates from photos when feasible.
  • Higher resolution photos are best suited for photo simulations.
  • Keep plenty of vertical room in your photography. Have knowledge of the proposed structure heights.
  • For photo simulations, typical shots are needed to help speed production in the office by standardization of process. A consistent angle of the field photos is a great benefit later in the process.
  • Avoid taking photographs facing the sun.


Typical Shots;         
1) Side view of the structure

2) 45° view of the structure

3) Front view of the structure

Using standard photograph angles allows for the photostimulation artist to reduce the number of unique equipment views created. This allows for more opportunities to “Cut & Paste” much of the equipment into the requested photostimulations.


Please check the requirements of your project however for specific typical shots to use. [When in doubt, get extra photos.]

Gathering Measurements

Calibrated Measuring Tool – CMT  [A visual approach]

A CMT (CVT Calibrated Visual Target) is a measuring device with markings at known distances apart as in the image below. Note that the CMT is flush with the ground and that the CMT is perfectly aligned and flush against the target structure.  It may be cumbersome however the taller the CMT, the more accurately the measurements can be obtained in office.

The benefit of using a CMT over a data-driven approach is that the results are reproducible from the photograph alone while the data-driven approach requires the photograph and the measurement data.

There may be occasions where one or both methods are required such as problem locations that are visually obstructed by plant life or other structures (cars, fences, etc.) or the base of the pole lies downhill out of view.



Range Finder/Height Stick  [A data-driven approach]


For accurate measurements to be calculated in the office there is a requirement of (2) TWO height locations per target structure. If there are multiple photos of the same structure the same (2) TWO measurements are valid for them all.

Ideal locations for measurements are visually significant and easy to see for instance; the bottom of a light arm mount, the mount location of utility lines. Notice these locations are on the pole and that locations to the side of the pole (transformers, insulators, etc.) are less accurate in the office for photo simulations.

1) Top of vertical pole sections

2) Entry Port / Attachment */ **/***

3) Metal Pole Section Joint **/***

4) Temporary Markings ***

  • * Attachments can be street signs, metal banding, or other equipment.
  • ** Must be visible in photos.
  • *** If no suitable markings can be found, utilize TEMPORARY markings, See the section below “Make-shift CMT”



CMT In-Depth

A CMT is a pole or a stick that has a predetermined amount of distance between visual markers. Typical markings are @ 12” of separation from each other and are of high contrast, typically red/white. The larger the CMT in both width and height, the greater the readability which brings a higher degree of accuracy in later calculations.

It is important that the CMT is flush against the pole. You may need to use bungee cords to temporarily hold the CMT against the pole. Ensure that the CMT is flush against the ground as well.

It is important that the CMT is vertically aligned with the pole as accurately as possible by eye. A small degree of difference at 60 feet distance can make a notable difference in calculations so it is important to try to reduce this amount when feasible.

When using CMT only (no physical measurements) image resolution of your photographs is important. The higher the photo resolution the more accurate the photo simulation can be. Please balance this with file size as the time required to transfer your data increases with resolution/file size as well.

Make-shift CMT

If you find yourself in the field with no CMT and still want a measurable photograph;

  • Utilize TEMPORARY markings such as tape, bungee cord or any other temporary and removable marking methods.
  • Use a tape measure to locate enough positions so that you have (2) known heights. Greater distances between markings will allow for higher accuracy when making measurements in office.
  • Mark these positions and note the distances in your field notes.
  • Take multiple photos as required by your project.
  • Remove the temporary markings.

Tools and Materials

  • Safety Vest
  • High MegaPixel Camera / Phone (Location Info On)
  • Tape Measure
  • Measuring Wheel / Range Finder
  • CMT or Equivalents
  • Painter’s Tape / Flagging Tape (Temp Markings)
  • Pen and Paper

Sample Sketch Pad Template