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I am writing some software to work with approach plates on a website, but I cannot find the scale of the plan view.

I am trying to convert the position of a plane in latitude and longitude onto the approach plate and keep it to scale.

If I knew how many miles wide each plate was or tall, I could make this happen.

Thank you for the help!

Approach Plate

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  • $\begingroup$ You can easily work out the scale by measuring the distance from CUTIS to the runway threshold, which you know is 4,6NM $\endgroup$ – J. Hougaard Jan 11 at 14:45
  • $\begingroup$ Related $\endgroup$ – Pondlife Jan 11 at 22:10
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FYI, what you're trying to do is called "georeferencing."

The scale for each plate is whatever is required to fit in all the relevant information without wasting space. Therefore, to properly geo-reference each plate, you will need to identify at least two points (e.g. CUTIS and CFVGK in this case), look up their lat/long in the published tables, and calculate the scale from there.

Note that some charts (more commonly SIDs and STARs than IAPs) are explicitly marked "NOT TO SCALE", which means this tactic can't work at all. And even some charts that are mostly to scale may have a few elements that aren't, usually transition fixes or navaids, marked by a double zigzag.

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    $\begingroup$ If the plate even has a scale. I believe I've seen some (but might have been SID/STAR plates only) that even explicitly mentioned they are “not to scale”. $\endgroup$ – Jan Hudec Jan 11 at 21:37
  • $\begingroup$ Thank you. I have decided to define two fixes on the chart by clicking on it, then click the corners where I want the plane to show, then using math, I can make everything scale properly. $\endgroup$ – Forseth11 Jan 12 at 0:17
  • $\begingroup$ Just to amplify Jan Hudec's comment, the proportions, or ratios of distance, between points even on the same plate may be different. This is what is meant by "not to scale". They are close, but some portions may be compressed to fit it on the same page, while keeping other key areas large enough to be readable. Think of the plate like a schematic, rather than a scale planform drawing. $\endgroup$ – Michael Hall Jan 12 at 5:52
  • $\begingroup$ @JanHudec Added. $\endgroup$ – StephenS Jan 12 at 16:41
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There is no set universal scale, every plate is to scale but with different scales. Essentially, they scale the place to show the representation required to orient the pilot. When these plates are printed out they may be resized by software, so even saying X mm is 1.25NM won't work.

It sounds like you might want to superimpose a plane on the plan view, which is going to be challenging in many ways. Detecting scale is possible by measuring distance between CUTIS and CFVGK as others suggest, however that will be difficult to do programmatically because these are meant to be interpreted by squishy carbon units. Look at CUTIS:

CUTIS is the place where the squiggly line meets the thin line cutting across the arrow. CUTIS Programmatically determining exactly where to start your scale measurement will be extremely difficult, if you have it wrong by a few pixels that will translate into the wrong scale and your airplane symbol in the wrong place. If you solve that problem for this plate there's hundreds more that look different. There's so many edge cases you'd have to code around, it's unlikely you'd ever get them all.

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