Hi Andrzej That is exactly right. In particular I agree that it should be {ele|height:m} as it has to have feet as the target unit. Since the default unit in OSM is meters even the :m part could be defaulted. ..Steve
some guessing on my part, hope someone corrects if I'm wrong.
As I understand, elevations in img are stored in feet.
Filters hight:m=>ft and conv:m=>ft indicate, that value from source has to be converted into feet, as expected by img format.
When you look at map, you see height units according to settings in GPS. You can set meters or feet. So for hight:m=>ft, these values are correct: ele=500, map: ", 500 m" = 1650ft, default conversion ele=500m, map: ", 500 m" = 1650ft, converted form meters ele=500ft, map: ", 152 m" = 499ft, preserved feet
Settings in GPS are valid only for some objects types and label content. Conversion in GPS is done, when label starts with numeric or numeric is prefixed by special separator (it is [0x1f] for cgpsmapper). I guess filter "hight:" adds separator and GPS converts it to ", ".
Now filter hight:ft=>m seems to be kind of useless. It converts feet to meters, stores this value in img and adds a prefix, indicating that value is in feet. What we need here, is no conversion but separator only. Maybe something like this could work: {ele|height:ft=>ft}.
Actually it always should be feet as a destination for height, we could simplify this filter like this: {ele|height:m} or {ele|height:ft}, indicating only default unit in source data.