Convert a list of NAD27 hddd.mm.mmm to WGS84 ddd.ddddd?

Former Member over 6 years ago

Hi there wizards!

I was sent a list of GPS datapoints recorded on a GPSMAP62 a few years back. I intend to use these datapoints to make sweetsweet science happen, but I cannot load them into ArcGIS without the projections turning out all wrong.
I figured out that if I convert them from the current format of NAD27 in hddd.mm.mmm, to WGS84 in hddd.ddddd I get the correct placement of datapoints. The issue is that I've only figured out how to do this one datapoint at the time in BaseCamp, and I have more than 500 points to convert.
Is there any way I can load a excel sheet of data into BaseCamp and run a conversion? Or am I stuck manually doing this the coming few nights?

One example is [TABLE="border: 0, cellpadding: 0, cellspacing: 0"]
[TR]
[TD="width: 88"]N18 07.228[/TD]
[TD="width: 98"]W87 50.436[/TD]
[/TR]
[/TABLE]
Should become the point below with correct conversion. [TABLE="border: 0, cellpadding: 0, cellspacing: 0"]
[TR]
[TD="width: 98"]N18.12047[/TD]
[TD="width: 98"]W87.84059[/TD]
[/TR]
[/TABLE]

Cheers guys

0 tmk2 over 6 years ago

Can't you set up ArcGIS to accept NAD27 coordinates? I don't use ArcGIS, so I cannot confirm, but I figure that this kind of software would have such an option.

In what form do you have the list of coordinates? Is it an excel file, a text file, something else?

0 Former Member over 6 years ago

If they were recorded on the 62, they can't by in NAD27. All data is changed to WGS84 when put in the GPX file. In addition, the file will state the datum used and all programs including Basecamp will read this and change to the cuurent datum automatically.

How about you share the source file and we can see what is wrong with it.

0 BTLAAKE over 6 years ago

The conversion you provided was degree minutes to decimal (e.g.. new lat value = 18 + 7.228/60). The correct conversion from NAD27 to WGS84 would have given a value of N18.12116 W87.84062. As mentioned above, a gpx file will always give WGS84 coordinates. It is possible that the provider output a MapSource text file which, I believe, would have maintained the NAD27 values.

If in fact you are looking to do a NAD27 to WGS84 for 500 points, you may want to go to the NGS website and look for the link to the geodetic tool kit. I believe the NADCON application will accept a file of points and convert them from NAD27 to NAD83. From Garmin's perspective, WGS84 and NAD83 are equivalent.