diff --git a/README b/README
index 8d3bc1e8..7dae6542 100644
--- a/README
+++ b/README
@@ -21,6 +21,15 @@ smaller chunks is much more doable though.
 Building the Tools
 ==================
 
+IMPORTANT: if you are compiling with gcc, I recommend that you compile
+the /Libs/TriangleJRS code without optimization (-O2).  Optimization can
+lead to problems for some tiles.  (Different numerical stability properties
+in the optimized code????) Usually I will go and remove the -O2 option (twice)
+from the Makefile after it has been generated from the Makefile.am file.  Be
+warned that any time you change the Makefile.am, or rerun autogen.sh or
+configure, you will have to go back and fix this particular Makefile.
+
+
 These tools are primarily compiled and tested under Unix with the Gnu
 C/C++ compilers.  I believe they also build and run on windows with
 Cygwin.  If anyone has patches for supporting other platforms, I will
@@ -74,11 +83,11 @@ TerraGear supports several terrain data sources:
    b) Then process the resulting files with "Prep/DemChop/demchop"
 
 
-4. SRTM (1 and 3-arcsec nearly world wide coverage):
+4. SRTM (version 1 & 2) (1 and 3-arcsec nearly world wide coverage):
 
    ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/
 
-   a) Chop up the .zip files using "Prep/DemChop/hgtchop"
+   a) Chop up each .zip files using "Prep/DemChop/hgtchop"
 
 
 5. 3-arcsec ASCII DEM files:
@@ -95,7 +104,24 @@ TerraGear supports several terrain data sources:
 The result for any of these terrain sources should be a "work" tree
 with a .arr.gz file for each FG tile.
 
-6. After you create the .arr.gz files you have to create a
+6. SRTM data comes with 'voids'.  These are areas where their
+   automated data processing system could not reliably determine the
+   elevation.  Often this happens over water, or over mountain peaks.
+   There is a big chunk of the Grand Canyon missing, a big chunk of
+   Rhode Island, etc.
+
+   So as a partial fix I came up with a little program that will fill
+   in the voids from another data source.  In this case the only thing
+   I half trust is the USGS 3 arcsec DEM data for the USA.  So we
+   can't fix voids outside the USA right now.
+
+   In the same directory as DemChop and HgtChop there is a "fillvoids"
+   program.  You might wish to run it with something like the
+   following command line:
+
+     find /export/fgfs05/curt/Work/SRTM2-North_America3 -name '*.arr.gz' -exec ./fillvoids {} /stage/fgfs05/curt/Work/USGS-DEM-USA-3 \;
+
+7. After you create the .arr.gz files you have to create a
    corresponding .fit.gz file for each of these.  This is a data
    reduction step which fits a set of polygons to the raw terrain with
    a set of constraints on the maximum error allowed relative to the