Huge File Workarounds

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 Mask database with shapefile Find points in areas (like an administrative boundary in a shapefile) 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.	QGIS will open the files rapidly. Use QGIS to export/subset, noting possible problems.
Raster	Option 1, when you need only part of the map extent Subset & zoom, File, Save DEM, Current subset, MD DEM Option 2, when you can afford a lower grid resolution Raster GIS: Thin (decimate DEM to lower spatial 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.	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: OpenGL Point cloud Slice: EW and NS slices through the point cloud. 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.

QGIS file subset geographically

Open QGIS
Open shapefile (Layer, Add Vector Layer) or a raster (Layer, add raster layer)
Zoom the map to the region you want
Right click on the layer in the table of contents, and select properties.
Pick export, and select the current map extent and other parameters

GDAL/OGR shapfile problems when subsetting geographically: The export option has issues we have not gotten around for some shapefiles (e.g. NASA MODIS fires). These appear to be in GDAL/OGR, because the same problems are in MICRODEM and QGIS which both use GDAL. Other files, like TIGER shapfiles, work fine.

Truncates the float fields in the dBase fields.
If you delete/rename the lat/long fields, you can import them from the shapefile's SHP file and you can work with the file except for any floating point fields

Last revision 2/3/2021