Image Overlays


When Maptitude creates a surface, it overlays an image of the current map onto the surface. In most of the examples in these pages, we have used the DEM colored according to elevation. More useful and interesting surfaces can be produced by adding additional layer(s) with different information. This additional information could include the standard Maptitude layers, allowing rivers, lakes, roads, cities, etc to be added. You could of course add your own vector information. However, this page concentrates on some examples where external imagery has been added.

There are a number of issues to bear in mind when using imagery layers with surfaces. First, you must make sure the imagery layer is on top – even above the DEM layer. Also make sure any other layers are hidden or fully covered up. It is very easy for ‘wide area’ layers such as Country to remain on and plant a large country name in the middle of your surface image!  Next you must make sure your surface is being created from a true gridded DEM. If you have a TIN (Triangulated Irregular Network), then you must grid it first. In theory a raw TIN should work, but there is a bug in Maptitude that will cause any imagery layers to be plotted with their axes reversed. Finally, both imagery and surface creation can consume memory, and can take some time to render. It is generally a good idea to limit the resolution or extents of both the imagery and the surface.

Our first example combines the Google Satellite imagery (Tools->Imagery->Web Map Layer->Google Satellite) with the Snowdonia dataset, to create a photo-realistic landscape:

A realistic rendering of the Snowdonia surface using Google Satellite imagery, and a vertical exaggeration of 2x: View to the West. Note the greys on the mid-left – these are the slate quarries and dumps that surround Blaenau Ffestiniog. Notice also how fields are only in the valley bottoms, and forests are constrained to medium gradient slopes. Click for larger view.

As well as landscape imagery, raster imagery with other information can also be applied. The following example uses the above Snowdonia DEM with a geological map derived from the British Geological Survey’s WMS Server:

The BGS ‘1:50K Solid’ geological map (via the BGS WMS server) overlain over the Snowdonia DEM. View is to the north west. Vertical exaggeration: 3x. Despite the pronounced glacial landscape, it is possible to see how some rocks (e.g. the igneous magentas, yellows, and oranges) tend to resist erosion. Click for larger view.

As well as online imagery (Google Satellite and WMS Server), local raster tiles can also be used. The following example uses GeoTIFF geological data (from the UT Bureau of Economic Geology’s NW Digital GAT Quad data) combined with USGS National Map DEM:

The Caprock Escarpment in North Texas, SE of Amarillo. View to the NW. Vertical exaggeration: 3x. Speckling is due to the imagery being originally derived from a paper product. Click for larger view.

This example clearly demonstrates how the geology influences the Caprock Escarpment. The top (beiges) consists of relatively recent Pliocene deposits – these are the High Plains. The escarpment cliffs are primarily Triassic ‘Dockum’ (magentas), that overly the Permian ‘Quartermaster’ (blues). The escarpment recedes as the Triassic erodes, undercutting the Pliocene. The yellow low-lying band in the middle are recent fluvial (river) deposits from the Prairie Dog Town Fork (of the Red River). This flows from the Palo Duo Canyon (rear, left).

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