Subscriber Discussion

A Way To Field Measure PPF With A Rubber Ball??

U
Undisclosed #1
•Apr 05, 2018

All the tools I have seen and used, tell us what the PPF “Should Be” given a particular camera. IPVM’s calculator can also let us pic the camera we need by adjusting the FOV and ppf range we want at a particular place within the camera view…. A very useful tool to me, an engineer. But how am I to actually find out  the field without trotting out one of those targets used in the UK that costs big bucks?

Someone told me about this method and I wanted to see what you think about it.

  1. Find a rubber ball of a known size (36” is what my friend told me).
  2. Place the ball in the center of the FOV for the camera you are trying to measure and at a point where the manufacturer (or calculator) says you see a given number of ppf.
  3. Zoom the image digitally until the pixels are clearly revealed.
  4. Count the number of pixels on the screen at the mid-point of the ball out, either across or down divide by 3 (for the 3’ ball). The result is PPF either vertically or horizontal.

This seems like it might work. What do you think. Could IPVM test this theory?

(2)
JH
John Honovich
•Apr 08, 2018
IPVM

Well, some camera manufacturers have PPF counters built in. If you just want to verify this technically, i.e., how many pixels cover a given area, this is a good approach.

From an Axis document:

The image above is a poor demo of the tool that they have that counts for.

As for using a ball, if I was to pursue that approach, i'd simply use a ruler, e.g., a 1 foot ruler. Export a snapshot from the camera and then use a graphics editor to select / count the area of the object (in my example the 1 foot rule); if the 1 foot ruler showed 55 pixels horizontally, I would then conclude it was 55pff.

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