TransDEM Forum

I've spent the last 2 days trying to create an KML overlay file for Google Earth that would provide a grid with a 720 meter spacing. I figured this would be neat to give a rough estimate right off the bat of how many Trainz baseboards would be needed as you are scoping out places to model right in Google Earth. I've tried a program called GEPath by R. Sgrillo, but even though I specified a grid spacing of 720 meters, measuring the result in Google Earth showed errors as great as ±30 meters. Then I tried a manual method using UTM coordinates (in increments of 720), but still have errors as great as ±10 meters.

While I'm learning a lot (always a good thing) about UTM coordinates, I've run out of ideas. Does anyone know of an existing KML file that has a grid with 720 meter spacing?

Thanks!

Andrew

Can you explain your overall objective a bit more? It's not quite clear to me why you need such a raster in Google Earth.

Well, when I look for a route to do in Trainz, I first go to Google Earth with the railroad layer on. I look for interesting interlockings or short lines, etc. Currently, I would choose an area and do the following with the goal of wondering how many baseboards am I looking at:

1) Draw a simple path in GE and save it as a KML.
2) Open TransDEM and download the corresponding Map Tile.
3) Import the KML path from step one.
4) Make a new flat DEM.
5) Turn on the "Show Trainz baseboards".

Example where minimally 5 x 4 baseboards would do nicely:



Now, not that I don't like using TransDEM of course , with a 720 x 720 meter grid available to me in Google Earth, I could shorten the above steps to just 1:

1) Turn on 720 x 720 m grid in Google Earth.

Here's the same area in Google Earth with the "GEPath" grid KML file that was created. As you can see it is close, but off by about 18 meters. I'd like something that is just as accurate as the "Show Trainz baseboards" in TransDEM.



I hope that explains my intentions better. Thanks for your time.

Andrew

The way I do it for all my tests is the same as in the TransDEM Quick Start Guide:

1. Begin with an overview map. I usually take Open Street Map for that. Acquire a single map tile at medium scale (zoom levels 12 to 14) in reasonable size, typically 1536 px for me.
2. Import that kml file.
3. Acquire large scale map clippings or orthoimages along the kml path.
4. Download DEM or create flat DEM.

But many ways lead to Rome.

I have used an UTM grid overlay for Google Earth in the past. You could probably search for that and analyze and possible adapt it to a 720 m grid. Note that TransDEM uses the same coordinate origin for baseboards as with UTM: Central zone meridian for easting and equator for northing.

That's a good suggestion. I'll try and find something like that. GEPro has a UTM grid built in, but it only shows zone boundaries and the "C" through "X" sub-zones at different latitudes.

I'll post a response if and when I come up with something useful.

Thanks!

Andrew