topic Re: Converting 2D raster scanned map to DEM in ArcGIS Spatial Analyst Questions

Converting 2D raster scanned map to DEM

ConorCahalane — Mon, 22 Apr 2013 09:32:40 GMT

I tried two really great tools this weekend, ArcScan and TopoToRaster. They do exactly what im looking for, but i would like to improve the results a bit.

I downloaded a sample contour map off the net

http://www.ducklakeproperty.com/images/map/Moon_Pond_detail.jpg

then used ArcScan to make the contours into vectors giving me this image

[ATTACH=CONFIG]23700[/ATTACH]

im happy with it, even though i could probably tweak it a bit using the hole and gap settings - and then i run TopotoRaster giving me this greyscale DEM.

[ATTACH=CONFIG]23701[/ATTACH]

but as you can probably see, the levels are off..it is coloured as lower when it should be higher and vice-versa. I'm guessing thats because the vector contours i used had no elevation field? The manual is a bit unclear - it seems to imply the contours are all you need, but surely you need a starting elevation? Do i need all elevations?

Any suggestions?

Thanks,

Conor.

Re: Converting 2D raster scanned map to DEM

DanPatterson_Retired — Mon, 22 Apr 2013 10:15:54 GMT

your lines do not have any elevations associated with them, hence, you won't be able to generate a DEM unless you can ascribe values to them

Re: Converting 2D raster scanned map to DEM

Anonymous User — Mon, 22 Apr 2013 10:31:55 GMT

Original User: con20or

Thanks Dan.

I tried it with another map, a colour one with lots of symbology on it, it didnt do half as well. First i had to convert it to grayscale so I could assign the 2 classes in the symbology tab which lowered the quality quite a bit. I played around with the settings too, increased tolerance etc, but no luck.

Re: Converting 2D raster scanned map to DEM

ConorCahalane — Thu, 25 Apr 2013 08:14:52 GMT

Seems this is a tough one to do with any sort of thematic detail on the map. If the map is in colour, you have to convert it from RGB to greyscale before you can change the display properties to classified, so you lose some detial there. Then when you lower the number of classes to two, you lose lots more, particularly if there are thin contour lines. I tried selecting the contours in GIMP and then putting them in a seperate image, but the requirement for two classes only still caused problems.

Any suggestions?

Re: Converting 2D raster scanned map to DEM

Anonymous User — Fri, 26 Apr 2013 16:10:48 GMT

Original User: erictrice

Why not just download a DEM for the area? Or use the Esri World Elevation Services... I strongly urge you to discontinue your current methodology.

Best Regards,
Eric

Re: Converting 2D raster scanned map to DEM

ConorCahalane — Mon, 29 Apr 2013 11:16:14 GMT

Hi Eric,

It's old historical mapping - the topography has changed significantly since then, a modern DEM would be no good.