Transdem and Google Earth question.

[Expyker]

If this has been asked before I apologize. Just point in the right direction and I will read it.

When using google earth images as a ground texture, what resolution must the images be to show up? Everytime I try to export a route I get the error message say that the images are greater than one pixel per 2.5 meters. Should I resize my images in Gimp before georeferencing them?

I am able to export the UTM tiles into trainz, but dont like them as well since my terrain isn't flat, therefore I get tiles sticking through in some areas.

So do I need to change images sizes for google earth or change grid sizes on the DEMs?

Thanks in advance

 

[jkfrench]

If you haven't already, there's a .zip file (including a .PDF that has a section called 'Getting the Right Google Earth Images') in the TransDEM forum's tutorials section ... it can be found here ... http://forum.transdem.de/viewtopic.php?f=6&t=105 ... the very first entry has a link to the .zip file. It might help you out. Sorry, can't help you past that since I haven't actually tried using Google Earth Images with TransDEM yet.

 

[Expyker]

Thank You for the reply, I think this is what I was needing.

 

[Expyker]

Yup, that's what I was looking for. It is still not as sharp as I would like, but it s gonna have to do. I wish I could get it as sharp as on the UTM tiles.

 

[geophil]

It is still not as sharp as I would like, but it s gonna have to do. I wish I could get it as sharp as on the UTM tiles.

That's not possible, due to the technical principle of ground textures in Trainz. Ground textures in Trainz are assigned per ground vertex and by index. That limits the number of available textures and textures have to be monochromatic for reusability. And by this, it limits scale to something like 1:25,000 for the 5m terrain grid. 1:25,000, however, is a bit low for aerial images. For this reason, I always recommend to use a cartographic map for ground textures.

 

[Expyker]

geophil, can a better result be gotten with orthophotography from a location like the USGS Seamless Server (or whatever it is called now)? Or is it due solely to the confines of the way Trainz configures the baseboard textures.

Danke Schoen

 

[geophil]

The problem is ground texture resolution in Trainz, or more correctly the way Trainz handles ground textures and its implications, see my previous post. That is independent of the ortho image source. The limit is 1 pixel per 5m (5m terrain grid). For a matching resolution in Google Earth, your eye altitude would be quite high, too high for the images to be useful for route building.

A theoretical explanation:
The difference between aerial photography and a cartographic map is the abstraction which makes up the cartographic map. The map can be seen as a filtered aerial image, with all the essential features already extracted. That reduces the amount of information and you need less resolution or lower scale.

Compare the two at the same scale: