Okay, what you want is a datafield which shows the MGRS of your position, except it is "adjusted" for a datum which is different from the "current" datum? Does that sound right?
There are some old maps out there with 1927 datum, and I've noticed that (at least in the states) the MGRS data is slightly offset from the newer circa 1984 datum. One way I have "fixed" for this problem is to add/subtract an offset value for the longitude offset and latitude offset.
Essentially, if all your MGRS grids are pointing to points that are consistently 14m N and 3m E (or something strange like that), from the points which you had saved - and you know the grids are correct - or the points are correct ... then it's a matter of applying the offset to get the "actual" value... or at least display it... or display the old value so you can use your old maps... if I think I know what you're talking about.. sound right?
as to the accuracy at elevation, I am not entirely clear it will match up, but such an app wouldn't be too hard to make. I would use a datafield though, just simpler to program.
Yes what i mean is changing the datum to meet my map that im using. i actually dont really bother about the elevation. I just want to set the datum to kertau 1948. Being able to change the datum will be the priority, is anyone able to create an app like this ?
//ya totally pseudo code here so it will not work at all as written..
var offsetX = 0.000034;
var offsetY = -0.000921;
// I can figure this out based on your offset...
// it'll be a float value equivalent to a degree of
// longitude or latitude, forget which is which...
//
// also, this function will need to know your latitude to determine the offset for longitude, explain later
function compute(info) {
var point = info.currentlocation;
point.initialize(
x = info.currentlocation[x].toFloat() + offsetX;
y = info.currentlocation[y].toFloat() + offsetY;
}
displayGeoCoords(MGRSformat);
}
I find nothing wrong with asking if someone wants to do something like this for the 735 (maybe just a data field to display the location in this format), as developers might just be looking for a new project to fill a need of users, and will do it for free.
--little disclaimer - this is the poor man's solution - I've done this before by hand and I know it can work with another map I've come across so I think it will work for your map. But there might be some easier solution elsewhere, I'm just a fan of land navigation... anyways---
Okay so, at some point before you get what you want, you're gonna have to figure out what the offset is. So to do that,
(1) find some key points on your map which you can also find on google earth satellite view, and in the first column on a piece paper, write descriptions for each of these points, and circle them on the map, whatever so you recall which points you chose... these will be our comparison points. For more accuracy you may need to do this at a number of points - say at least three... like ten would be a whole lot better, assuming you can find ten points you can match from map to satellite imagery...
(2) in the next column labeled "NEW" write the MGRS and lat lon coordinates from GOOGLE MAPS or another legitimate online source, as accurate as possible using satellite imagery or whatnot. We will use the lat lon because that is the "native" coordinates that Garmin uses on its devices. We will use the MGRS to test afterwards that it is working.
(3) in the next column labeled "OLD/MAP" write the MGRS and lat/lon of the SAME POINTS taken from the PHYSICAL map you are using. You may need to plug in the MGRS grids into a conversion site to get the lat/lon, if your map only shows MGRS. Search for such sites using google.
(4) Compare the virtual "NEW" lat/lon with the "OLD/MAP" lat/lon as reflected on your physical map, and write the differences down in the next column labeled "DIFFERENCE"
(5) apply those offset values to your datafield. It would be easy to create your own datafield. So assuming you cannot do that, you can message me the offset lat and lon values and then either myself or someone who gets to it first can write something quick... I can I'll do it... essentially the pseudocode is gonna look like this:
//ya totally pseudo code here so it will not work at all as written..
var offsetX = 0.000034;
var offsetY = -0.000921;
// I can figure this out based on your offset...
// it'll be a float value equivalent to a degree of
// longitude or latitude, forget which is which...
//
// also, this function will need to know your latitude to determine the offset for longitude, explain later
function compute(info) {
var point = info.currentlocation;
point.initialize(
x = info.currentlocation[x].toFloat() + offsetX;
y = info.currentlocation[y].toFloat() + offsetY;
}
displayGeoCoords(MGRSformat);
}
sound like what you're looking for?
I may not get around to writing anything for another day or two, but in the meantime you can use some math... (assuming your map doesn't cross complex MGRS zones should be pretty easy) just conduct step 4 using the MGRS coordinates, and you'll need to apply the difference to the first and the second half- so lets say your map was 400m south and 18m east of what it "should" be per what google maps says, well then all you have to do is add 400 to your "map" grids, and (add or subtract forget) 18 to your longitude MGRS section, in order to get the "new" grid... if that makes sense. but, it's easy to implement, so hopefully I can get something for ya. Maybe if there's some mapping expert reading this they can chime in with a simpler solution.. but if not this might be the ultimate poor man's solution, but it should work. (note: this solution should work for YOUR MAP, but DON'T ASSUME it will work for anywhere outside your map!)
There's nothing wrong with asking.
However, my personal opinion – as a consumer, and a staunch believer in consumerism – is that if a consumer is not willing to spend money on satisfying a want or need, and also not willing to invest time, sweat and tears (so to speak) to make it happen himself/herself, then obviously he/she does not perceive it as something important or worthwhile to acquire, and so it's quite reasonable for others to see it as not being worthwhile to provide.
If I were inspired to develop something like that purely for the intellectual challenge, I still wouldn't be offering the end product to someone who accords it no personal worth (being what he/she is prepared to offer in exchange). That's the point I was really making to would-be developers who are reading this discussion, and not as a rebuke to the requestor just for asking.
i see some logic in your explanation, however why i need to have a function to change the datum used by the gps is because ill be navigating in closed terrain(jungle) , i will not have internet access but only gps access. So i dont think its feasible to use ur method out in the field. Or maybe someone can create an app which allow user to plug in the readings from a WGS84 mgr to convert into a different datum ? possible ?
