EXTRACT THE DIGITAL ELEVATION MODEL DATA

How do you extract Data Elevation Model (DEM's) from the supplied PSB databases with CONVERT?

To extract a DEM file from the supplied data on disc, the Convert program allows you to select a specific area and take the compressed PSB data file and output DEM format for selected latitude and longitude area, and specified geographic projection. Be aware that the size of DEM files can be extremely large - a 1 km PSB file has compress 4 CD-ROM's of DEM data, i.e. over 2 Gb.

Load the INSTALL disc and open the Global Data. Select the appropriate 1 km, 2 km, 4 km or 10 km folder, the higher intervals, 10 km, give the coarser view and smaller files.

On the World Map display, define the area of interest. Select Western boundary longitude, Eastern boundary longitude (note West of Greenwich is expressed as a negative), Northern latitude boundary, Southern latitude boundary (Southern latitudes are expressed as negatives). Select geographic projection from the 29 variations provided.

IMPORTANT---Select output file name and output disc area. Check that the disc is a writeable area (default is write back to CD which will abort), and that there is sufficient free space available. Then activate Convert.

It is recommended that you install MapRender3D Pro or Lite before running Convert. The MapRender3D software installs DLL's which are used as part of the Convert process.

How do you extract Data Elevation Model (DEM's) from the East and West USA 100 Meter databases using CONVERT?

To extract a DEM file from the supplied data on disc, the Convert program allows you to select a specific area within the USA or the entire database. Convert will take the compressed PSB data file and output DEM format for selected latitude and longitude area, and specified geographic projection. Be aware that the size of DEM files can be extremely large - a 100 meter USA PSB file has compress 12 CD-ROM's of DEM data, i.e. over 8 Gb.

Put the CD-ROM disc in the drive and open the Windows Explorer. Highlight the appropriate USA100E.PSB or USA100W.PSB files, right-click and select OPEN - do not double-click MRC.EXE

On the Map display, define the area of interest. Select Western boundary longitude, Eastern boundary longitude - note West of Greenwich is expressed as a negative which will apply to all USA territory, Northern latitude boundary, Southern latitude boundary (Southern latitudes are expressed as negatives and you should not have any negative values for US coordinates!. Select geographic projection from the 29 variations provided.

Note that the maximum boundaries for the USA database are 24 to 50 North and -64 to -125 West. There is substantial overlap btween the East and West disc to avoid the possibility of partial Central USA selections.

IMPORTANT---Select output file name and output disc area. Check that the disc is a writeable area (default is write back to CD which will abort), and that there is sufficient free space available. Then activate Convert.

It is recommended that you install MapRender3D Pro or Lite before running Convert. The MapRender3D software installs DLL's which are used as part of the Convert process.

RENDERING THE MAP

How do I build 2D and 3D terrain models using DEM data with MAPRENDER3D?

Open MR3D. Select the relief color scheme by Opening Settings. Select one of the .REL files, initially NATURAL.REL or CLASSIC.REL might be most suitable for a first pass.

Select the DEM file, created either from Convert (above) or from another source such as the USGS / Internet.

Changing the sampling value when loading height data determines how many points in the height data grid are used in displaying maps. A sampling value of 2 means that every second point will be used; a sampling value of 5 means that every fifth point will be used. If a small map is to be created from a large area, then it is advisable to reduce the number of points in the grid. This will improve the rendering speed of the map. The sampling resolution of a file can only be changed by reloading the file.

Setting the min/max values in the Height data loader settings dialog will adjust the color gradient in the Settings window so that the colors are distributed according to the maximum and minimum height values found in the height data file. Sometimes, a set of maps is required where the same color gradient is used in all the maps. If a number of country maps are created that should have the same look, then adjusting the color gradient based on maximum and minimum heights should not be checked. But if you want to create a new map for a different area of the world using an already existing color gradient, where the height data for the new map is very different to the original, then adjusting the color gradient is often useful.

In the MapRender3D settings box, set sampling resolution to Low for the first pass. If this generates an acceptable color, use "All Data" to get the best resolution of the data, i.e. each DEM data point will convert to one pixel rather than every second, fourth or tenth point.

The DEM file will have a high and low elevation height that will determine the unique color relief settings file graduation for each map. The setting heights may have to be reset to get sea level at +0 meters or feet. Double-click on the one of the heights nearest sea level of the color scale, move up or down the scale and reset the height of the blue (or other color indicating sea level).

If processing a set of adjoining maps, select the DEM file with the highest elevation and reset the REL file for this map to the highest elevation, and keep this same setting for all the other adjoining maps to maintain the same elevation color scheme. When a height file is loaded, do not check the reset after loading button.

The REL file can be edited in an ASCII editor to provide your own layers of color. Each elevation band corresponds to a set of 4 values, a H value for the height, an R, G and B value which is the 0 thru 255 value divided by 1. For instance R value 128 would be set up in the table as 0.500000   Make sure you adjust the ColorMapSize= to reflect the number of sets of entries in the newly created color scale. Save the new REL file with a new name.

[HEIGHT_RGB]
ColourGradient=0
ColorMapSize=8
HRGB_00_H=0.000000
HRGB_00_R=0.500000
HRGB_00_G=0.768627
HRGB_00_B=0.600000

Click here to copy a "Cartographic" styles relief settings file - you can modify and set this file up in your Styles directory.

For 3D viewing, switch the mode to 3D and click on the plane to rotate or orient the terrain to a new viewing position. This is best done in low or med resolution until satisfied with the perspective, then rendered at high resolution finally. Note that it is not necessary to render at high res to save the final image - images are saved at the highest resolution regardless of viewing resolution.