TransDEM Forum

Hello Roland,

I am just getting started with TransDEM and have had success with the Trainz tutorials. However, I am having difficulty with Tutorial 1 in the TransDEM Manual (page 118) "Georeferencing a Raster Map".

I am sure that I have set: VIEW|National Coordinate Systems|Swiss-Grid, but when I select the grid intersection for the first point in the lower left, I am not getting coordinates 685000 / 211000 as indicated.

I am getting numbers like 344183 / 360935, and consequently, when I do all four points the magenta grid does not line up with the black grid on the image. I am sure that I have ZOOM off, and have also discovered that I am getting some significant variance in the numbers on each attempt at 4x zoom with the mouse-wheel.

I have checked to see if there was any setting that I might have overlooked from the Trainz tutorial, but there doesn't seem to be anything that I can tell would cause this.

I cannot think of what else to try with my limited experience.

Thank you for your assistance.

This tutorial is about manual georeferencing, i.e. we must add the proper coordinates ourselves. Since we deal with a plain bitmap here, TransDEM has no real clue what geo coordinates might apply to this particular bitmap. Hence, TransDEM makes a very simple guess for the first coordinate point, but guesses for ensuing points will become better with each point.

So, tutorial step 3c needs our keyboard input, as will steps 3d and 3e.

You did see the "Quick Start Guide" chapter in the TransDEM Trainz manual? It bypasses manual geo-referencing altogether and points you directly to the fast lane. However, there is nothing wrong with tutorial 1 first. It's there for a purpose, to illustrate how TransDEM handles maps. This may help to better understand the basics even if we mostly use the more automated functions with implicit geo-referencing.

Thank you Roland,

Well of course I feel silly now, as that should have been obvious to me.
Do the magenta numbers shown, 685 / 210 have any real-world significance?
...just in case I do have to do this method at some point.

Thank you again for your patience.

MarkusP

geophil wrote:Do the magenta numbers shown, 685 / 210 have any real-world significance?

Yes, they do. You would find these grid line labels on the original paper map at the margins. Almost every coordinate system for topographic maps has a metric grid, even in countries where imperial measurements still rule. And 1000 m grid lines are quite common.

Once you have completed a few other tutorials, you could compare the geo-location of this map-clipping to another geo data source for the same area, like Open Street Map or an ortho-image. And you should find that they will match (hopefully ).