Polygons: .mpa, .mpap#(3.X), .pc#, .tp#, .cd#, .sg#, .sc#, .dom, .dm#, .tbt, .tb#
The GDB library supports Ilwis table and vector files for import. An Ilwis table and vector data set consists of several different files.
Ilwis tables consist of a .tbt file with associated .tb#, .dom and .dm# files.
Ilwis pointmap (points) data set consist of a .mpp file with associated .pn#, .tbt, .tb#, .dom, and .dm# files.
Ilwis segmentmap (line) data set consist of a .mps file with associated .cd#, .sg#, .sc#, .dom and .dm# files with a possiblity of having an associated table.
Ilwis polygonmap (area) data set consist of a .mpa file with associated .pl#, .pc#, .tp# and segmentmap files.
GDB does not currently support any Ilwis symbolic representations.
If there is an associated .csy (coordinate system) file, the translator will search for, and read the file to get the projection definition. At this time, the only projections recognized by the translator are UTM, Albers EqualArea Conic, Azimuthal Equidistant, Equidistant Conic, Lambert Azimuthal EqualArea, Lambert Conformal Conic, Miller Cylindrical, Mercator, Oblique Mercator PolyConic, Robinson, Stereographic, Sinusoidal and Transverse Mercator. All other projections will be treated as generic meters.
In Ilwis 2.0 a pointmap was a table with three columns, X (double), Y(double) and Value. In 3.0 the map is still a table but there are only two column: a column of the type coordinate and a column of the value type (same as 2.0). The coordinate column is stored as pairs of consecutive doubles (X,Y). The actual binary file is the same as the old format but for Ilwis its organization is different. One note, the extension of the file has been changed to .pt#.
Here the changes are quite extensive. Gone are CD# and SG# file that accompanied the mps file. There is only one data file with the mps is file the mps# file. The file has the same structure as a table file in Ilwis.
The mps# file is a table with 5 columns. The first column gives the Minimum value of the coordinates (X,Y) of the bounding box, both doubles. The second column has the maximum coordinates(X,Y) of the bounding box., both doubles. The third column gives the actual coordinates of all the points of the segment (including begin and end). This field has a variable size. The first number is the number of bytes that is used for the field (long). Then all the coordinate in pairs of doubles (X,Y) follow. The number of coords times 16 gives the number of bytes used. The fourth column states if the segment is deleted or not. It is stored a long with a 1 indicating it has not been deleted and 0 indicating it has been deleted. The last column contains the value of the segment. This may be either a raw value or a real value (double).
Polygon map data files have been redesigned along the same lines as segment files. In this case there are two data files. The mpap# and the mpat#. The first file is a table that contains data of the polygon. The second contains the data of the topology.
The structure of the mpap# is a table with 7 columns. The first two columns are the same as for segment maps, the bounding box. The third column is the area of the polygon (double), the fourth column is the length of the boundary (double). The fifth column gives an index in the topology file (see below) indicating where the topology for this polygon starts in the topology file. This index is a long. The sixth column gives the value of the polygon (raw value) and the last column states if the column is deleted.
The structure of the table can be seen in the mpa file of a polygon map. There is a table section there with all of its corresponding columns.
The second data file contains the topology information of the map. It is basically the same as the mps# file with some extensions and no value column. The file is again a table with the first four columns the same as the mps#. After that four columns are added: Which polygon is to the left, which is to the right and forward and backward link of the polygon segment. The links are indexes in the table just as the left and right polygon are in the polgyon table (first file).
The columns of the topology table can also be found in the mpa file. The table sections have the prefix 'top:'.
© PCI Geomatics Enterprises, Inc.®, 2023. All rights reserved.