Why is the horizontal scale incorrect?

I've posted a similar question before. So far, it's had 57 views but no replies. I really would be grateful if someone could check this out on their computer screen and let me know.

The error is quite simple: the horizontal scale is 96% of the vertical scale. For example, if I use the ruler tool to draw a 5 km straight line, vertically it is 23.3cm while horizontally it is 21.1cm. Looking at the screen, the kilometre squares of the Ordnance Survey are obviously not square. The vertical scale is “correct” because it matches the scale at the bottom of a map printout. The error is there whether an .img map is showing, or whether a UK Ordnance Survey overlay is showing.

I’d be most grateful for any light anyone can throw on this, if only just to measure a line on your screen. It is BaseCamp 4.8.11. I have tried this on an iMac (OS Mojave) and a MacBookAir (OS Big Sur): it is the same on both machines. Is there some simple setting that I have overlooked?

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JaVaWa over 2 years ago +1

BaseCamp uses a projection where the middle of the map is displayed correctly. When you go up or downward on the map it will be distorted more or less. It depends on the vertical distance; maps that cover…

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0 SUSSAMB over 2 years ago

I've deleted your other post so we don't have 2 on the same problem.

0 NevWG over 2 years ago in reply to SUSSAMB

Thanks. I'm sorry to have posted twice, but I really would like to know if this is just me, or it's a systematic error in BaseCamp.

0 JaVaWa over 2 years ago

BaseCamp uses a projection where the middle of the map is displayed correctly. When you go up or downward on the map it will be distorted more or less. It depends on the vertical distance; maps that cover a large area will be distorted more at the upper and lower edges.

You can fix it with JaVaWa GMTK by setting the projection to the nearest rounded latitude, however this program will work only on your Mac with Mojave. For Macs with a newer OS there is another solution: https://www.javawa.nl/projectionmac.html

These solutions apply to on the Mac installed maps, for maps that are read from you device by BaseCamp you will need another one: JaVaWa Device Manager. This program has the same problem as GMTK: it is not supported on MacOSes newer than Mojave... I don't have a workaround like the one I posted above.

0 NevWG over 2 years ago in reply to JaVaWa

Thanks! I shall explore that. It does seem odd that BaseCamp should use a projection that distorts in this way. I'm not aware that any other similar programs do the same.

0 JaVaWa over 2 years ago

The info and the utility on the page https://www.javawa.nl/projectionmac.html have been updated; now you can adjust the projection for maps on devices too (on Macs with the latest MacOS)

0 SUSSAMB over 2 years ago in reply to JaVaWa

Good to see you back

0 NevWG over 2 years ago

Hi JaVaWa,

I ran SetProjectionAngle and got an error message:

Not authorised to send Apple events to System Events. (-1743)

I added SetProjectionAngle to the list given Full Disk Access under Security & Privacy, but that didn't help.

0 JaVaWa over 2 years ago

It doesn't need full disk access, it needs the possibility to send system events. See image below.

0 NevWG over 2 years ago in reply to JaVaWa

Thanks!

0 NevWG over 2 years ago in reply to JaVaWa

Sorry, there is no +/- under the list of apps: how do I add SetProjectionAngle to the list?