Is there a formula to convert from the page and grid of Thomas Bros to latitude / longitude?

Question

I am working on a project that contains a Thomas Brothers Map page and grid numbers. Is there a way to programmatically convert maps from this page to latitude and longitude?

An example would be for the intersection of the US101 and I405 motorways.

ThomasBrothers: 561-3G (page-grid)

Answer 1

Not that I know, but I don't have much experience with Thomas bros cards. Are you talking about a printed version of the maps or is there a link somewhere in the online map?

If you just need a few lat / longs, you can find places matching the grid and get lats and longs manually on many websites, including http://itouchmap.com/latlong.html

If you provide a link to the Thomas bros card you use, I may be able to help further.

By looking at the link above, you can determine that US 101 and I-405 have a latitude of 34.16073390017978 and a longitude of -118.46952438354492.

Answer 2

Your best source will be the publisher of the map. If they want to help, someone can tell you exactly what you need to know. If they do not help you, they are unlikely to pass this information on to anyone else.

If this is the case, you can do some work manually to adjust one point from the map grid to your target coordinate system. In fact, you can rebuild the "datum" display for each page. You also need to know which projection map was used to render the maps so that you can calculate the conversion from map coordinates to geographical coordinates when moving away from your "source". Finally, you will need to set the orientation of the map, as there are different concepts of "north".

It seems like Thomas’s maps use a new grid for each page, rather than continuously passing the grid from page to page. If this happens, you will have to map one point on each map. For example, find a place where the intersection of the map grid coincides with a noticeable intersection of roads. Then you can find the intersection coordinates of the roads using a map with latitude and longitude (topographic map, TerraServer , etc.). Doing this with two points on the same vertical grid line should help you establish the north used on the map.

Answer 3

The short answer is that each of the nine areas has a grid derived from the conformal projection of the Lambert cone with custom parameters, so you cannot write a conversion program without parameters.

Answer 4

I also have ThomasBros. pages that I would like to convert to lat / long for searching in the Google Maps API. They also provided something called TBXY ... not sure what it is - maybe some notation for GPS / lat / long?

<Area>"El Cajon"</Area> <ThomasBrothers>"1297 5E"</ThomasBrothers> <TBXY>"6481390:1827008"</TBXY> 

Answer 5

Maps Thomas Brothers invested a lot in developing their GIS system to create their digital mapping system. Although the first “digital model" was Sacramento County 1990, development began back in 1986. I expect their map projection projections to be the well-guarded trade secret that Rand McNally now owns. I would not know these equations, but I would also like to know them.

There are 9 projections covering 48 states. If you know the equations for Los Angeles, it really is in California and Nevada. Oregon and Washington have their own forecasts. Arizona, New Mexico, Colorado and Utah have yet another forecast.

I know it...

As many people know, the page grid is an exact square of 1/2 mile, or 2640 feet by 2640 feet. The coordinate unit is 1 foot.

To determine the coordination of Thomas Brother XY, you will receive one or more Thomas Guide CD cards that have recently been discontinued. The latest ones released for some California counties were the 2008 release. The latest releases for Seattle, Portland, Las Vegas and Phoenix / Tucson were the 2007 edition. Each one is still available on the Rand McNally website for $ 20.

When you geocode a group of addresses, you will see the output file with the coordinates TGXY and Lat / Lon for the addresses you specify, as well as the page and the grid. When this file is open, you can click on the map to add additional geocoded points, which will also contain both coordinates. The output file is saved in the Access.mdb database file.

If you know a lot about map projections or solid geometry, a set of appropriate TGXY and Lat / Lon coordinators will provide you with some good test data.

As you mentioned San Diego, I provided its bordering coordinates. West x = 3062760 East x = 3086520 North y = 0985040 South-y = 0966560

This is not in the "TBXY" range that you found on Google. Perhaps this is the same projection with a shifted origin.