Now shunting through the input rv if it's valid but there is no parallax.

Author: msdemlei

expected/epochprop.out

@@ -1,4 +1,4 @@
-SET extra_float_digits=2;
+SET extra_float_digits = 1;
 SELECT
        to_char(DEGREES(tp[1]), '999D9999999999'),
        to_char(DEGREES(tp[2]), '999D9999999999'),
@@ -45,9 +45,9 @@ FROM (
                NULL,
                RADIANS(-801.551/3.6e6), RADIANS(10362/3.6e6), -110,
                -100) AS tp) AS q;
-     to_char     |     to_char     | to_char | to_char  |  to_char   | to_char 
------------------+-----------------+---------+----------+------------+---------
-  269.4744079540 |    4.4055337210 |         | -801.210 |  10361.762 | 
+     to_char     |     to_char     | to_char | to_char  |  to_char   | to_char  
+-----------------+-----------------+---------+----------+------------+----------
+  269.4744079540 |    4.4055337210 |         | -801.210 |  10361.762 | -110.000
 (1 row)
 
 SELECT

sql/epochprop.sql

@@ -1,4 +1,4 @@
-SET extra_float_digits=2;
+SET extra_float_digits = 1;
 
 SELECT
        to_char(DEGREES(tp[1]), '999D9999999999'),

src/epochprop.c

@@ -184,14 +184,23 @@ epoch_prop(PG_FUNCTION_ARGS) {
 
 	propagate_phasevec(&input, delta_t, &output);
 
+	/* If we have a null parallax but a good RV, preserve the original,
+		untransformed RV on output.  See
+		https://github.com/ivoa-std/udf-catalogue/pull/20#issuecomment-2115053757
+		for the rationale. */
+	if (!PG_ARGISNULL(4) && PG_ARGISNULL(1)) {
+		output_null[5] = 0;
+		output.rv = input.rv;
+	}
+
 	/* change to internal units: rad, rad/yr, mas, and km/s */
 	retvals[0] = Float8GetDatum(output.pos.lng);
 	retvals[1] = Float8GetDatum(output.pos.lat);
 	retvals[2] = Float8GetDatum(output.parallax);
 	retvals[3] = Float8GetDatum(output.pm[0]);
 	retvals[4] = Float8GetDatum(output.pm[1]);
 	retvals[5] = Float8GetDatum(output.rv);
-
+	
 	{
 		int lower_bounds[1] = {1};
 		int dims[1] = {6};