If you have a very large file, it takes a long time for operations, and you
only need part of the data.
File Type |
MICRODEM native solutions |
QGIS solutions If you installed GDAL,
you should have QGIS as well |
Vector shapefiles |
Open a map,
Subset
& zoom to the region you want. You have three choices:
- Subset DB before opening it in MICRODEM
- File, Import, Shapefile
after subset to match map extent. You can adjust the map
extent first to cover your area of interest.
- This uses GDAL/OGR, with
possible problems.
- The file will be loaded. It will be in a
subdirectory of the directory with the initial shapefile.
- Filter the file ASAP
- Open the shapefile.
- Abort drawing if it is taking too long
- Filtering options
- Map query, Current map area:
- Filter: the DB as desired
if there are fields in the DB that will do the job
- Edit, Mask--based on geometry
- Report,
Shapefile export
for line/areas, or Export DBF Table for points.
- current map extent option
- current filter option
- Open the new file and close the original file.
- Open in QGIS, extract just the portion you need, and open
that. If the file is too big for MICRODEM, it is likely to be
very slow in QGIS as well.
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QGIS will open the files rapidly.
Use QGIS to export/subset, noting
possible problems.
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Raster |
- Option 1, when you need only part of the map extent
- Option 2, when you can afford a lower grid resolution
- Option 3, when the input file is too big to open (say a
compressed Geotiff; probably has to be geographic)
- Open a map,
Subset
& zoom to the region you want.
- File, Import, Raster after subset to match map extent
- Option 4: open in QGIS, and subset there.
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QGIS will open the files rapidly.
Use QGIS to export/subset.
The export option produces a smaller file that works easily. |
Lidar |
- Turn off Immediate map on the
File list tab.
Subset
& zoom immediately to just the area you want to see.
This is particularly important for:
- Draw tab, thin map, either manual or
automatic. Remember to check that this is adjusting as you zoom in,
when you want to see all the data.
- Consider
Creating grids
if they will do what you need.
- Subset very large files. Instead of having to
look at every point for every operation
- As you zoom in, you will only have to look at a few tiles.
- Some operations can be multi-threaded, meaning they will run in
parallel.
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