TransDEM and Rastor Map Help?

[JIb228]

So here's my dilemma. I've whipped up a DEM in Transdem and Used a Google Earth tutorial form a few years back to add google images as my rastor maps. So for so good right? But as I work my way along I have noticed some of the maps not lining up right.

Now I've pressed "R" and "N" in Google Earth to reset the view rotation. I am at a 5km zoom level. (5.00km to be exact.) I've saved the image and the location. I've imported them in to TransDEM and converted them to UTM tiles. But at this point I am stumped. I'd just roll with them being slightly off, but after 1 or 2 images my track work starts to get wonky.

Any advice?

 

[geophil]

So here's my dilemma. I've whipped up a DEM in Transdem and Used a Google Earth tutorial form a few years back to add google images as my rastor maps. So for so good right? But as I work my way along I have noticed some of the maps not lining up right.

It's quite likely that some of your placemarks are not right in the center of your images. That's something TransDEM cannot detect. But if the placemark is not where it should be, georeferencing will go wrong.

The Google Earth procedure with placemarks is error-prone. The method is easy to understand and you quickly get a first result, that's why many peole start with it. But for real productive work I can only once again suggest to try Map Tiles. For good reasons, the TransDEM Quick Start Guide recommends using that interface for raster maps/ortho-images and also points to tutorial #7 in the TransDEM main manual which provides the "how-to".

See my postings in the neighboring thread for more on this subject and an example: http://forums.auran.com/trainz/show...sDEM-for-route-creation&p=1550136#post1550136

 

[oknotsen]

Now that geophil has replied, would you (Jib) mind sharing where that location is that you are showing in your image?
I think I vaguely remember it from some Google Earth scouting but can't recall where.

 

[JIb228]

It's quite likely that some of your placemarks are not right in the center of your images. That's something TransDEM cannot detect. But if the placemark is not where it should be, georeferencing will go wrong.

The Google Earth procedure with placemarks is error-prone. The method is easy to understand and you quickly get a first result, that's why many peole start with it. But for real productive work I can only once again suggest to try Map Tiles. For good reasons, the TransDEM Quick Start Guide recommends using that interface for raster maps/ortho-images and also points to tutorial #7 in the TransDEM main manual which provides the "how-to".

See my postings in the neighboring thread for more on this subject and an example: http://forums.auran.com/trainz/show...sDEM-for-route-creation&p=1550136#post1550136

I'll take a look at that. When I put down the place mark then save the image I dont move the camera. But I'll check out the other post and see what I can do.

Now that geophil has replied, would you (Jib) mind sharing where that location is that you are showing in your image?
I think I vaguely remember it from some Google Earth scouting but can't recall where.

That's UP's Yermo yard, just a bit east of BNSF Barstow.

 

[Chris750]

Those google images are much better than the default raster maps/UTM, much more detail eh. I will have to look into using them next time. Glad all is worked out, your route looks interesting.

 

[geophil]

Those google images are much better than the default raster maps/UTM, much more detail eh. I will have to look into using them next time. Glad all is worked out, your route looks interesting.

I arranged Google Earth and Google Maps next to each other.

Acquiring the map tile image (Google Maps Static API, new in TransDEM 2.6.1 and Google key required):



Now combined in the TransDEM main window:

• Upper right: Google Maps ortho-image, map tile at zoom level 15
• Lower left (and partially overlapping the other image): Google Earth, with the placemark method, eye alt. 5.5 km

It's the same data source for both, but different projections. In Google Earth it's a geometric vertical perspective projection, in Google Maps it's the standard for map tiles, Mercator onto a sphere, with the GRS80 semi-major axis as the radius. TransDEM sorts that.

 

[Chris750]

Sorry Phil, I don't have a clue what you said above. You know your stuff that is for sure, but it confuses me to no end. I have basically tried to learn Transderm by trial and error myself. Won't be using it for a while, still have a lot of scenery to put down in my Medicine Hat route.

Cheers.

 

[geophil]

I don't have a clue what you said above.

In your original statement you compared Google images to something else. That else wasn't clear.

There are many different sources for raster maps and/or ortho-images which will work with TransDEM. What I compared in my reply were Google ortho-images, obtained in two different ways, via Google Earth and via Google Maps.

For Google Earth, you run the program Google Earth, set placemarks and take screenshots. You then open the placemarks in TransDEM and let TransDEM georeference the screenshot. It's a semi-manual way, with a number of interactions within Google Earth.

For Google Maps, you will use the Map Tile client in TransDEM, which allows a more automated approach, basically just two clicks per image, after navigation. The Map Tile client requires a one-time setup, and you will need a (free) Google API key, but after that, Google Maps will be a very efficient source.

In both cases, you have the same Google ortho-imagery at your disposal, it's only the interface to the data source that is different.