Mapping Hacks

Map Wardriving (and other!) Data with MapServer #92

Chapter 8, Building the Geospatial Web

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HACK

created, while tileitem specifies the column containing the file locations.

Again, MapServer’s web site explains all of this in more detail.

Throw this in your map file as the first layer. This will place the aerial pho-

tographs on the bottom and draw the shapefiles on top:

layer

name aerial_photos

type raster

status default

tileindex "aerial"

tileitem "location"

end

Projection Issues

In a sense-making world, our shapefiles and GeoTIFFs would be using the

same coordinate system, and we would be done at this stage. Unfortu-

nately, even though our data comes from the same place, our images are

being plotted thousands of miles apart (or more).

Fortunately, MapServer has the enormously powerful ability to reproject

both raster and vector layers for us on the fly. If we define a

projection sec-

tion at the top level of our map file as follows:

projection "+proj=utm" "+zone=17" end

Then we can add a similar projection section within each of our latitude/

longitude layers, like so:

projection "+proj=latlong" end

The combination of the two will prompt MapServer to dynamically

reproject those layers into UTM Zone 17, as needed. Meanwhile, the DOQs,

which were already in a UTM projection, will remain unchanged, and every-

thing should magically line up. Of course, before that happens, we will first

have to adjust ...